Citation
Aggression and familiarity as factors in mate selection in Peromyscus polionotus and Peromyscus maniculatus

Material Information

Title:
Aggression and familiarity as factors in mate selection in Peromyscus polionotus and Peromyscus maniculatus
Creator:
Webster, Daniel George, 1948-
Copyright Date:
1983
Language:
English

Subjects

Subjects / Keywords:
Animal nesting ( jstor )
Animals ( jstor )
Breeding ( jstor )
Ecology ( jstor )
Female animals ( jstor )
Inbreeding ( jstor )
Mating behavior ( jstor )
Mice ( jstor )
Siblings ( jstor )
Species ( jstor )

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
09818074 ( oclc )
ABZ0641 ( ltuf )
0029088854 ( ALEPH )

Downloads

This item has the following downloads:


Full Text












AGGRESSION AND FAMILIARITY AS FACTORS IN
MATE SELECTION IN Peromyscus polionotus
AND Peromyscus maniculatus






BY

DANIEL GEORGE WEBSTER


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


1983































To my wife Carole and my daughter Danielle
and to my parents















ACKNOWLEDGEMENTS


Many individuals have generously contributed to this work, and

while these individuals deserve much of the credit for its completion,

any faults which may remain are my own. I thank Dr. D. A. Dewsbury for

his support and suggestions, for providing a critical scientific

atmosphere in which to conduct research, and for his example as a

scientist. I would also like to thank Drs. H. J. Brockmann, C.

VanHartesveldt, and W. B. Webb for their encouragement and support, and

for contributing of their time and knowledge. I particularly thank

Dr. M. E. Meyer whose consistent encouragement and support were a major

factor in my completion of the Graduate Program and the present work.

Several of my fellow students also contributed to this work. My

appreciation to D. Kim Sawrey, Bruce Ferguson, Larry Shapiro, Allen

Hodges, and Denis Baumgardner, for their support, encouragement and

critisms. I would especially like to thank Dean Williams for his time,

and for his patience in explaining some of the mysteries of electronics

to a neophyte. Our animal caretakers, T. C. Fryer and I. Washington,

also deserve my appreciation for the excellent care they have given my

animals. Last, but most of all, I would like to thank my wife Carole

who has supported me through the bad times and the good, and my daughter

Danielle whose patience and understanding exceed her years.

This research was funded in part through NSF Grant BNS78-05173 to

Dr. D. A. Dewsbury.















TABLE OF CONTENTS



PAGE

ACKNOWLEDGEMENTS ................................................. i

ABSTRACT ..................................... ...... .............. vi

SECTION

I INTRODUCTION .............................................. 1

Aggression as a Factor in Mate Selection .................. 4
Familiarity as a Factor In Mate Selection ................11
Kin Familiarity ...................................... 12
Familiar Others .. .................................... 14

II GENERAL EXPERIMENTAL CONSIDERATIONS AND METHODOLOGY ......18

Selection of Species ....................**............... 18
Approaches to the Study of Social Preference ............. 19
General Experimental Information .............*........... 22
General Methods ........................... ** ......... *25
Subjects ........... -..............................- **25
Apparatus ......................................... ** ..26
Seminatural apparatus ................................ 26
Preference apparatus ................................. 29
Aggression apparatus ................................. 32

I I I EXPERIMENTS ................ ..................* ........ 35

Seminatural Experiments ............................. ... 35
Introduction ........................................ 35
Subjects ................... ......................... *36
Procedure ............................... *.......... ** 36
Results .............................. ............... *40
Discussion ........................................ **61
Aggression and Familiarity Preference Tests ............. 63
Introduction ....... ............... ................ .. 63
Subjects ............ ............................. ***63
Procedure ................. .......................... *64
Results .................. ..................... .... 67
Discussion ......... .............................. ***78










Sibling Preference Tests ............................... 81
Introduction ........................................... 81
Subjects ....... .................................... 82
Procedure ........................................... 82
Results .............................................. 83
Discussion ........................................... 90

IV GENERAL DISCUSSION .................................... 92

Aggressive Ability as a Factor in Preference ............. 93
Ecology, Mating System, and Aggressive Abillty ......... 94
Peromyscus maniculatus ............................... 95
Peromyscus pollonotus ............................... 101
Aggression and Mate Selection ......................... 106
Intraspeclfic aggression ............................ 106
Interspecific aggression ........................... 108
Early breeding ..................................**** 109
Bruce effect .......... ............................ *109
Heritable aggressive ability ........................ 111
Familiarity as a Factor In Preference ................... 113
Prior History ......................................... 114
Ecology and Social System -........................... 115
Peromyscus maniculatus .........**.................. 115
Peromyscus polionotus ........*..................... 117
Kinship as a Factor in Preference ......................* 119
Inbreeding In Peromyscus maniculatus .................* 120
Evidence for and against inbreeding ................. 120
Ecological and social factors ..................... 121
Inbreeding In Peromyscus pollonotus ................... 125
Evidence for and against inbreeding ................. 125
Ecological and social factors ..................... 126
Evolution of Monogamy in Peromyscus Pollonotus ......... 129
Summary ..... ....................... .................... 133

REFERENCES .......... .............. .............** ..... 137

BIOGRAPHICAL SKETCH ....................................* 162














Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy


AGGRESSION AND FAMILIARITY AS FACTORS IN
MATE SELECTION IN Peromyscus polionotus
AND Peromyscus maniculatus

By

Daniel George Webster


April 1983



Chairman: Donald A. Dewsbury
Major Department: Psychology


Aggressive ability and familiarity were examined as factors in

the social preference and mate selection of males and females of the

monogamous species polionotus, and the polygamous species P.

maniculatus. The aggressive behaviors and nesting behavior of P.

polionotus were observed in a seminatural apparatus; factors assessed

were 1) familiarity based on cohabitation, and 2) aggressive ability

as determined through aggressive interactions. Groups observed were

composed of either two pairs of familiar opposite-sexed individuals,

or two unfamiliar animals of each sex. Preferences of both species

were assessed in an automated preference apparatus. In addition to

the two factors assessed in the seminatural apparatus, the effects of

familiarity based on relatedness were assessed in the preference

apparatus. Measures recorded were the number and duration of visits









to stimulus animals. In the seminatural setting E. pollonotus of

both sexes displayed aggression, and nested more frequently with the

more aggressive of two opposite-sexed individuals. Males of this

species also exhibited a behavior, aggressive digging, that may

signal their aggressive status. Peromyscus polionotus and P.

maniculatus of both sexes exhibited evidence of preference for more

assertive opposite-sexed individuals (high rather than low tendency

to interact) in the preference apparatus. Peromyscus maniculatus of

both sexes also displayed preference for individuals of the opposite

sex that they had previously been housed with, but such familiarity

did not affect preference in P. polionotus. The lack of a

significant effect of familiarity on preference in P. polionotus was

consistent with the nesting behavior of this species in the

seminatural apparatus. Differences in the responses of P.

maniculatus and P. polionotus to familiar individuals may be based on

differences in the opportunities individuals of these species have to

use this factor in mate selection.

Peromyscus polionotus females demonstrated significant

preference for siblings over nonsiblings, and males tended to display

higher sibling than nonsibling scores. Inbreeding in EP polionotus

may permit individuals of this species to found populations in

isolated patches of favorable habitat. Lack of significant

preference by P. maniculatus for siblings or nonsiblings was

interpreted as due to competing preference responses in this species.















SECTION I
INTRODUCTION

The success of an organism in leaving a numerous
posterity is not measured only by the number of
its surviving offspring, but also by the quality
or probable success of these offspring. It is
therefore a matter of importance which particular
Individual of those available is to be their other
parent.(Fisher, 1958, p. 143)

Few factors are as important to an individual's reproductive

success as is the selection of a mate. Mate selection involves more

than simply the identification of potential partners as to species and

sex. In order for an individual to maximize Its future representation

in the gene pool it must also select the "best" possible mates on the

basis of a variety of other considerations.

There has been much theoretical speculation on the proximate and

ultimate bases of mate selection and on the relative Importance of

mate selection to different mating systems. In the last decade a

considerable effort has been made to collect empirical data on mate

selection, but large gaps still remain in the existing data which must

be filled before many important theoretical problems can be resolved.

Particularly lacking are data on male choice and data on mate

selection in mammalian species, especially those considered to be

monogamous. The lack of data on male choice probably stems In large

part from a traditional emphasis on female choice and male-male

competition (Bateman, 1948; Daly & Wilson, 1978; Trivers, 1972;










Williams, G. C., 1966) and the belief that male choice was either

nonexistent or negligible In the face of this competition. More

recently, however, It has been suggested that mate selection should be

of some consequence to males as well as females (e.g., Dewsbury,

1982c). The lack of data on monogamous mammalian species may be due In

part to two factors that make it somewhat difficult to observe these

species: 1) monogamy appears to be uncommon in mammals (Alexander,

1974; Crook, 1977; Kleiman, 1977; Orians, 1969) and 2) most mammals,

especially the smaller species, are largely nocturnal (Vaughan, 1978).

Study of the proximate factors Involved in mate selection is

extremely important to the resolution of issues about the evolution and

relative importance of mate selection in various mammalian taxa.

Factors that have been proposed to be of major importance to mate

selection are of two general types: those related to the genotype of a

potential mate, such as genetic quality (Trivers, 1972, 1976; Zahavi,

1975), and relatedness (Maynard Smith, 1956); and those related to

resources, such as the ability to accrue resources (Trivers, 1976) and

parental investment (Bateman, 1948; Trivers, 1972). The relevance of

any particular factors as criteria In mate selection will vary among

species, between sexes, and across mating systems, as a function of

differences in a group of interrelated variables Including ecological

factors (Borgia, 1979; Emlen & Orlng, 1977; Halliday, 1978).

Differences in the degree to which individuals of various species

utilize particular factors as criteria in mate selection would be

expected to reflect differences in the adaptiveness of those criteria

to mate selection in those species. Comparative studies of mate










selection or social preference in different species, therefore, can

provide an empirical basis for evaluation of hypotheses on the

importance of various factors to mate selection under different social

or mating systems. Such comparisons would be most effective when the

species compared were closely related (King, 1970) so that the species

do not differ in so many respects as to obscure the relationships of

interest.

Two factors of the sort that might be expected to be of broad

importance as criteria for mate selection across most species, but may

be expected to vary in importance among species, are the aggressive

ability of a potential mate, and that animal's degree of familiarity

with the individual expressing choice. An individual of high

aggressive ability could be defined as one that is highly competent in

the performance of aggressive behavior (i.e., displays, threats, and

fights). Individuals of high aggressive ability would be expected to

perform well in competition for contested resources and defense of

mates and/or offspring. Familiarity can be of two types, these are 1)

familiarity gained through exposure to other unrelated individuals, and

2) familiarity with kin. In the first sense, familiarity may provide a

basis for evaluation of former mates or a means of discriminating

between two potential mates. In the second sense, familiarity may

provide a basis for avoidance of inbreeding, or as a yardstick for

comparison of potential mates (Bateson, 1978, 1980).

This study was designed to provide data on the importance of

aggression and familiarity as factors affecting mate preference in

males and females of two closely related species of muroid rodents with










different mating systems: the monogamous species Peromyscus polionotus

and the polygamous species Peromyscus maniculatus. In light of the

relative lack of data on mate selection in monogamous species the major

focus of this study is on P. polionotus. The discussions that follow

provide a brief review of relevant theoretical factors in mate

selection, and a demonstration of the importance of aggression and

familiarity as factors in mate selection, with an emphasis on mammalian

species.

Aagression as a Factor in Mate Selection

Darwin (1859) recognized that some males could gain a reproductive

advantage over other males by defeating them in fights for females. It

has been suggested (Bateman, 1948) that the evolution of male-male

competition had its basis in differences in male-female strategies of

investment in gametes. Males are generally considered to invest little

energy in the production of gametes, whereas females invest a great

deal (Bateman, 1948; Orians, 1969; Stacey, 1982; Trivers, 1972).

Because of their larger investment females are valuable to males, and

the probability that females will obtain mates is high, but their

reproductive success will be limited by the number of gametes they can

produce. Males, however, because they invest little energy in the

production of individual gametes, can afford to produce large numbers

of gametes--with which they could potentially fertilize large numbers

of females. A male's reproductive success, therefore, may be greatly

influenced by the number of females he mates with--and males may be

expected to compete to fertilize females (see however, Dewsbury, 1982c;










Nakatsuru & Kramer, 1982). This argument was extended by Trivers

(1972), who restated it in a more general form based on the overall

relative level of parental investment of the two sexes, which he

hypothesized to determine the intensity of male-male competition in

species as well as the form of the mating system (see however, Kleiman

& Malcolm, 1981, p. 371; Wickler & Seibt, 1981). The level of

success achieved by a male in competitive mating may often depend upon

his ability to dominate other males. This notion has been examined in

a wealth of studies, recently reviewed by Dewsbury (1982b), on the

relationship between "dominance" and various aspects of reproduction.

A male's ability to conquer other males, however, also provides

females witn a basis by which to judge him against other males--a

basis for "female choice" (Darwin, 1874). Borgia (1979) has suggested

that a female's best indication of the relative overall genetic quality

of a male is provided through his aggressive interactions with other

males. Females choosing aggressive males, or allowing such males to

mate with them, may in effect be selecting "good genes" for their

offspring (Maynard Smith, 1956; Trivers, 1972). Selection for good

genes has also been suggested as a basis for the evolution of extra-

vagant sexually dimorphic characteristics (Fisher, 1930), as a basis

for lek behavior (Borgia, 1979), and as a basis for female choice in

Drosophila (Partridge, 1980). The major obstacle to the use of

heritable factors as a basis for choice is the problem of "using up"

the genetic variance for a trait (Krebs & Davies, 1981; Maynard Smith,

1978). Several factors, however, have been suggested to act to

maintain genetic variance; these include 1) advantages for










heterozygotes (Borgia, 1979), 2) variation in the optimal genotype in

space and time (Krebs & Davies, 1981), 3) factors such as chronic

parasitism, that may result in cyclic changes in the optimal genotype

(Hamilton & Zuk, 1982), and 4) rate of mutation in polygenic characters

(Lande, 1976).

The northern elephant seal (Mirounaa angustirostris) provides an

example of the importance of male aggressive ability in female choice

in a natural setting. During the breeding season males of this species

establish dominance hierachies which are maintained through threat and

combat. Dominant males guard groups of females from other males, and

account for the majority of first copulations (LeBeouf, 1974; LeBoeuf &

Peterson, 1969). Females help insure that they will be inseminated by

an aggressive dominant male by vocalizing loudly if a subordinate male

attempts to mount. The dominant male, alerted by the female, drives

off the subordinate male and copulates with the female (Cox & LeBoeuf,

1977). The authors note that females of many polygynous species might

be expected to incite male-male competition in this manner. Cox (1981)

has observed that female elephant seals are less likely to vocalize If

the male mounting them has just displayed dominance over another male

and suggested that females may thus select for males that frequently

display their aggressive ability. Cox hypothesized that in general "in

species where social status of males Is correlated with their genetic

fitness, female choice is likely to be based on social signals which

are used in competition between males" (p. 197). Similar hypotheses

have been proposed by Borgia (1979) and Alexander (1975). Cox (1981)

has provided examples of several species in which females appear to use

male's aggressive signals toward each other as a basis for choice. The










list consists of a fairly diverse array of species including

territorial birds (Armstrong, 1973; Thorpe, 1961), tree frogs (Whitney

& Krebs, 1975a, 1975b), sticklebacks (Tinbergen, 1951), and a

lek-forming bird, the ruff Philomachus pugnax (Hogan-Warburg, 1966).

Male aggressive ability need not be heritable or manifest at the

time of mating to be an important factor in female choice. Male

differences in aggressive ability, for example, will be related to

differences in their ability to acquire and hold territories (Brown, J.

L., 1964). A female choosing a male with a superior territory is in

effect also choosing a male that has been able to first obtain that

territory in competition with other males, and further to maintain it

in the face of threats from other males.

Female preference for aggressive males has also been demonstrated

in laboratory choice tests. Sexually experienced female brown lemmings

(Lemmus trimucronatus) in estrus were found, in olfactory choice tests,

to prefer dominant over subordinate males (Huck, Banks, & Wang, 1981).

Female preference was also predictive of male performance in later

dominance tests; estrous females again preferred dominant males while

diestrous females preferred subordinate males. The authors found that

dominant males had heavier testes and higher testosterone levels than

subordinates, and they hypothesized that female choice might be based

on differences in androgen dependent male odors. Estrous females were

also found to exhibit more copulation with dominant males in

tether-choice tests (Huck & Banks, 1982).

Costanzo and Renfrew (1977) studied the preference of sexually

experienced and naive female rats for dominant and subordinate male










odors. Ovariectomized sexually naive females displayed no preference

in hormonally induced estrus. Ovariectomized sexually experienced

females preferred dominant males when not injected with hormones, but

subordinate males when in hormonally induced estrus.

As discussed earlier a female may often invest relatively more than

a male in offspring, and a female's reproductive success may often be

more limited than a male's. Because of these factors females are

generally considered to be more choosey than males when selecting mates

(Bateman, 1948; Burley, 1977, 1981; Daly & Wilson, 1978; Trivers,

1972; Williams, G. C., 1966) and the majority of studies of social or

mate preference have been studies of female choice. Male reproductive

success, however, depends on not only the number of mates males acquire

but the quality of these mates as well (Wade, 1979). Rails (1976) has,

for example, suggested that larger females may often be better mothers.

Factors such as this might be considered trivial if males were capable

of inseminating an unlimited number of females. However, although

males appear to produce an enormous number of sperm and therefore to

be capable of inseminating an enormous number of females, these sperm

are emitted as ejaculates--of which a male may produce only limited

numbers (Dewsbury, 1982c; Nakatsuru & Kramer, 1982). Mate selection

may, therefore, often be of some consequence to males as well as

females (Dewsbury, 1982c).

The aggressive ability of females may be an important criterion for

male choice. Females with high aggressive ability may be more capable

than females with low ability in such behaviors as defense of young or

nest sites, or in competition for food items. Males of some species










have also demonstrated an ability to discriminate the aggressive status

of other individuals, and therefore the potential to use this factor in

mate selection. Male rats, for example, spend more time investigating

odor from a dominant male than from a subordinate (Krames, Carr, &

Bergman, 1969). Male mice also discriminate between the odors of

dominant and subordinate males (Carr, Martorano, & Krames, 1970) and

investigate areas marked by dominant males less than those marked by

subordinate males (Jones & Nowell, 1973). Both male and female

saddle-backed tamarins investigate dominant male scent marks more than

those of subordinate males (Epple, 1973, 1974).

Although the majority of preference studies to date have been

conducted with polygamous species, there is no reason to believe that

members of monogamous species should be any less adept at

discrimination based on differences in aggressive status, or that the

ability to make such discrimination should be any less useful to

members of monogamous species. Aggression serves many of the same

functions in monogamous species as in polygamous species. Although

male-male competition and aggression near the time of copulation may be

less important in monogamous than in many non-monogamous species,

aggression serves many functions at other times in an organism's

lifetime, and success in these other aggressive encounters will be just

as important to monogamous as to polygamous males. For example,

defense of resources critical to raising young, and in many cases to

initially attracting a mate, is hypothesized by some authors to be

universally displayed by males of monogamous species. Kleiman (1977)

states that "The male's territorial defense, which prevents the over-










utilization of necessary resources, is practiced by males of all

monogamous species" (p. 54). Kleiman (1977) has also indicated that

females of monogamous mammalian species may commonly be as involved as

males in territorial defense and contrasts this behavior with a lack

of territorial defense by non-monogamous females. This hypothesis is

similar to one previously proposed by Wilson (1975) as one of the

biasing ecological conditions for monogamy that two adults are

required to defend valuable resources contained in the territory. If

monogamous females help to acquire and defend resources then monogamous

males may do well to choose aggressive females as mates.

An additional consideration, related to the possible function of

aggression as a factor in mate selection in monogamous species, is the

"early breeding" hypothesis proposed by Darwin (1874). According to

this theory the most healthy, more dominant members of a species will

come into breeding condition earlier in the season, and establish

territories earlier, than the less vigorous subordinate individuals.

The more dominant individuals of each sex should then choose each other

as the "better" mates in preference to subordinate individuals. Two

species whose behavior may support the occurrence of this form of

selection are the artic skua (Stercorarius parasiticus) and the

mourning dove (Zenaldura macroura). Individuals generally pair for

life In the arctic skua (O'Donald, 1959). Darker males of this species

tend to breed earlier than birds of light or intermediate phenotype,

and females breeding for the first time are more successful with dark

males. Early breeding and large territory size are both correlated

with early hatching, and success of new pairs with dark males may be










related to male ability to hold large territories (Davis & O'Donald,

1976). Dominant male mourning doves prefer dominant females in

experiments with penned populations (Goforth & Baskett, 1971).

Dominant pairs breed earlier than subordinate pairs, and more offspring

of dominant pairs survive.

Based on theoretical considerations, and on the results of

research conducted to date, predictions can be made as to the relative

importance of aggression as a factor In mate selection in species with

polygamous and monogamous mating systems. Males that are above average

in their aggressive abilities should generally be preferred as mates by

females of monogamous and polygamous species. Females of monogamous

species, because they may form long-term pair bonds and consequences of

their choice may therefore be more long-term, might be expected to

display stronger preference than polygamous females. Males of

monogamous species might be expected to display preference for females

with higher aggressive ability because, among other considerations,

such females may be in breeding condition earlier and might be expected

to better share responsibility for territorial defense. Polygamous

males might also prefer females with higher aggressive ability because

such females may be better able to defend young or resources necessary

for raising young, but preference should not be as critical for these

males as for monogamous males.

Familiarity as a Factor in Mate Selection

Familiarity could be an important factor in mate selection In

several ways. It would be expected, for example, that early

familiarity with conspecifics should aid Individuals In discriminating










between members of their own and other species. Familiarity could

additionally be an important factor in recognition of kin, and

therefore a factor of importance in kin-selection and in avoidance of

inbreeding. It may also be of importance to animals of many species to

be capable of discriminating between unrelated strange and familiar

individuals. Two aspects of familiarity, recognition of kin and of

familiar others, will be discussed further.

Kin Familiarity

Bateson (1978, 1980) has hypothesized that early experience with

kin Imprints individuals to aspects of both kin and species, and that

such kin familiarity is important to selection of mates of the

appropriate species and to avoidance of inbreeding at sexual maturity.

Avoidance of inbreeding Is an important consideration in mate selection

because inbreeding often leads to inbreeding depression--a reduction

in the viability of inbred offspring and/or of their ability to

reproduce. Inbreeding depression has been documented in a variety of

species from ungulates (Rails, Brugger, & Ballou, 1979) to rodents

(Hill, 1974), birds (Bulmer, 1973), and Drosophila (Maynard Smith,

1956). In many mammalian species inbreeding is avoided in part because

individuals of one sex emigrate from the natal group before sexual

maturity. This type of emigration has been observed in chimpanzees

(Pusey, 1980), lions (Bertram 1975, 1976), olive baboons (Packer,

1979), black-tailed prairie dogs (Hoogland, 1982), and a variety of

other species. Intergroup transfer of individuals in mammalian species

and the significance of this behavior to avoidance of inbreeding have

recently been discussed by Packer (1979). Emigration from natal groups










may be mediated by adult aggression in many species (e.g., langurs:

Suglyama, 1965; elephant-shrews: Rathbun, 1979). However, female

(and male?) choice has also been suggested as a factor (Hoogland, 1982;

Wittenberger, 1981) since Individuals should be selected to emigrate

from natal groups If 1) relatives refuse to mate with them and 2)

alternative mates are not readily available. In at least some rodent

species reproductive maturity may be inhibited by pheromones produced

by adults (Bedlz & Whitsett, 1979; Drickamer, 1979; Lawton &

Whitsett, 1979; Lombardi & Whitsett, 1980). For young of such species

emigration from the natal group may provide the major opportunity for

reproduction.

Although it would appear that avoidance of inbreeding should

generally be the rule, certain circumstances may favor inbreeding. If

Inbreeding were not detrimental, individuals could increase their

inclusive fitness through mating with relatives (Bengtsson, 1978;

Maynard Smith, 1978). Female control of the sex of offspring in the

wasp Euodynerus foraminatus may be used to counterbalance the

detrimental effects of inbreeding and allow individuals of this

species to take advantage of the increase in relatedness resulting from

inbreeding (Cowan, 1979). Bengtsson (1978) hypothesized that it would

be adaptive for individuals to inbreed if the costs of inbreeding were

lower than the costs that would be incurred in dispersal or in

competition for mates in the natal group. Costs incurred through

dispersal would include such factors as increased exposure to predators

and to unfavorable environmental conditions. Inbreeding may also at

times be suited to specialized environmental situations; as noted by










Mayer (1970) "An outbreeder may also be so well buffered that it

stagnates evolutionarily. At the other end is the extreme inbreeder

which has found a lucky genotypic combination that permits it to

flourish in a specialized environmental situation (p. 245).

Shields (1982) compared the advantages and disadvantages of

outbreeding, inbreeding, and asexual reproduction and concluded that

inbreeding is often more advantageous than commonly assumed and should

be "expected to be common in organisms produced by stable lineage-

environment associations" (p. 274).

Although inbreeding may be adaptive under particular circumstances

individuals of most species should, given a choice, prefer to breed

with nonsiblings rather than siblings. Some support is lent to this

statement by the observation that the initiation of breeding in sibling

pairs is often delayed in comparison to the initiation of breeding in

nonsibling pairs (Batzli, Getz, & Hurley, 1977; Dewsbury, 1982a;

Hill, 1974; McGuire & Getz, 1981). The contribution of preference per

se to these findings is, however, difficult to assess. Animals in

these studies were not allowed a choice of mates and delayed

reproduction, or lack of reproduction, may result from several factors

(Dewsbury, 1982a) in addition to preference. It would be expected that

reproductively mature males and females of most species should prefer

to associate with nonsiblings rather than siblings, and that this

preference should be apparent in choice tests.

Familiar Others

Differences in familiarity need not only be defined in terms of

differences in relatedness, differences in familiarity may also be










defined in terms of differences in the amount and type of contact an

individual has had with others. Familiarity in this sense is an

important factor in many aspects of an animal's behavior, including

mate choice. Individuals should improve their reproductive success

by retaining mates that they have previously bred successfully with

and choosing unfamiliar others over mates with which breeding has

previously failed. Coulson (1966), for example, found kittiwakes

(Rissa tridactyla) were much more likely to change mates if breeding

had been unsuccessful; and red-billed gulls (Larus novaehollandiae

scopulinus) exhibit similar behavior (Mills, 1973). Although some

authors (e.g., Halliday, 1978) have indicated that mate choice based

on previous reproductive performance should only be of importance to

species which pair bond for more than one season, all that is

actually required is an ability to recognize previous mates. This

ability has been demonstrated in several species including rats

(Carr, Demesquita-Wander, Sachs, & Maconi, 1979; Carr, Hirsch, &

Balazs, 1980; Krames, Costanzo, & Carr, 1967), lemmings (Huck &

Banks, 1979) and prairie voles (Ward, Baumgardner, & Dewsbury, 1981).

The ability to recognize previous mates may also enhance reproduction

through allowing earlier breeding. This function of familiarity

has generally been stressed for monogamous species (e.g., Daly &

Wilson, 1978; Wilson, 1975).

The advantages of familiarity to mate selection, based on

reproductive performance or early breeding, are related to an

individuals previous breeding experience. Familiarity may, however,

also bias selection of mates by sexually Inexperienced individuals.










Females may, for example, require a male to exhibit some evidence of

"commitment" to forming a pair-bond prior to copulation. The male

may fill this requirement by investing a large amount of his time in

the relationship, and thus preclude his finding another female

(Maynard Smith, 1977), and/or by demonstrating his ability to provide

resources (e.g., Nisbet, 1973). Evidence of commitment is likely to

be most important to members of monogamous species, especially those

in which individuals form prolonged or lifelong bonds, because many

individuals of these species may only choose a mate once in their

lifetime. Individuals of species that form prolonged pair bonds

might also be expected to be more "prepared" (Seligman, 1970) to

recognize differences in familiarity, than would be individuals of

species that do not pair bond, if familiarity were important to the

maintenance of pair bonds.

Many authors have indicated that males of polygamous species

should mate with as many different individuals as possible (Adler,

1978; Bateman, 1948; Dawkins, 1976; Williams, G. C, 1966; Zucker &

Wade, 1968). Although as noted previously males may have a limited

capacity to mate and should therefore be somewhat selective when

allowed a choice of partners (Dewsbury, 1982c; Nakatsuru & Kramer,

1982), it may still often be to a males advantage to obtain

additional matings if the opportunity is presented. Familiarity may

therefore be of importance (at least to polygamous males) in

identification of females a male has already mated with. However,

because mate infidelity could have serious consequences for

monogamously mated individuals (Grafen & Sibly, 1978; Trivers, 1972),










it is likely that individuals of monogamous species have been

selected to detect potential philanderers, and to select against such

individuals as mates (e.g., Erickson & Zenone, 1976). It may be

expected therefore that polygamous males would be more likely than

monogamous males to prefer novel over familiar partners. This

prediction is consistent with previous suggestions that males of

monogamous species should be less likely than males of polygamous

species to exhibit a "Coolidge effect" (Thomas & Birney, 1979;

Wilson, Kuehn, & Beach, 1963; but also see Dewsbury, 1981a,b).

As a general set of predictions it might be expected that

individuals of monogamous species would display greater preference for

familiar individuals than would individuals of polygamous species.

Because of differences in the consequences of choice it might also be

expected that females would display stronger preference than males

(e.g., Burley, 1981). Monogamous females would be expected to display

the strongest preference for familiar individuals. Monogamous males

should be expected to display some preference for familiar

individuals, as might also polygamous females (unless greater benefits

result from producing multiply sired litters). Polygamous males,

however, due to a greater possibility of increasing their reproductive

success through mating with more than one female, may be expected to

display some preference for novel individuals of the opposite sex.















SECTION II
GENERAL EXPERIMENTAL CONSIDERATIONS AND METHODOLOGY

The discussions in this section provide a brief rationale for the

choice of the particular species and experimental procedures that were

followed in this study. This section provides general methodological

Information common to all experiments in this study, and a description

of the apparatus used in these experiments.

Selection of Species

One of the methods that may be particularly suited to exposing and

interpreting differences In social behavior among species Is the

comparative approach (Dewsbury & Rethlingshafer, 1973; King, 1970).

Murold rodents are a group that is particularly suited to the use of

the comparative method (Dewsbury, 1974, 1978). The two murold rodent

species that were chosen for comparison in this study, the monogamous

Peromyscus polionotus (oldfleld mouse) and polygamous Peromyscug

manlculatus (deer mouse), are both members of the maniculatus species

group of the subgenus Peromyscus. Because the majority of mammalian

species are considered to be non-monogamous (Alexander, 1974; Crook,

1977; Kleiman, 1977; Orlans, 1969) and relatively little information

is available about mate choice In monogamous mammalian species, It was

considered to be particularly Important that one of the species

selected for comparison in the present study be a monogamous species.

Although monogamy has been suggested for several rodent species,










"except for polionotus, the data are circumstantial" (Foltz, 1981a,

p. 665) and are open to more than one interpretation. Data supportive

of monogamy in P. polionotus include the consistent finding that the

majority of reproductively mature individuals are captured as

heterosexual pairs (Blair, 1951; Foltz, 1981a; Rand & Host, 1942;

Smith, 1966), and behavioral (Blair, 1951) and electrophoretic (Foltz,

1981a) evidence that pairs form long-term reproductive associations.

Information about mate selection in this species was also considered to

be of importance, in addition to comparative considerations, because

one subspecies, the beach mouse (PE polionotus leucocephalus), is

presently considered endangered.

In contrast to P, polionoQus, electrophoretic evidence indicates

polygamy for P. maniculatus (Birdsall & Nash, 1973; Merritt & Wu,

1975) and females may even, on occasion, raise young communally

(Hansen, 1957). Dewsbury (1981c) suggests that maniculatus may be even

more promiscuous than indicated by electrophoretic studies because

these studies do not consider the effect of factors such as

"differential fertilizing capacity" (Lanier, Estep, & Dewsbury, 1979)

that may affect estimates of the number of matings that have occurred.

Approaches to the Study of Social Preference

Ideally social behavior and social preference should be studied in

natural settings. Although this approach may be utilized successfully

with diurnal and highly visible species, it is often an impractical, or

nearly impossible, approach for many species. As an alternative

investigators have often turned to the study of populations in outdoor

(Agren, 1976; Boice, 1977; Boice & Adams, 1980; Gipps & Jewell,










1979; Jannett, 1980; Lidicker, 1980) or indoor (Bowen & Brooks, 1978;

Crowcroft & Rowe, 1963; Getz & Carter, 1980; Hill, 1977; Poole &

Morgan, 1976; Reimar & Petras, 1967; Thiessen & Maxwell, 1979;

Thomas & Birney, 1979) seminatural enclosures. While these enclosures

do not replicate natural conditions in many respects, they do allow the

investigator to approximate some aspects of the natural setting, and

allow a degree of control over experimental variables that is generally

not available in nature.

Even in a seminatural apparatus, however, interactions may often

be so complex that it is difficult to evaluate the effects of any

single variable on a particular behavior such as social preference.

This problem has led investigators to the use of even more controlled

situations, such as preference apparatus of various types, to evaluate

the role of various factors in social preference. In the typical

preference paradigm an animal (the "choice" animal) is allowed to

express preference by "choosing" between two or more alternative

stimuli. Behavioral measures of preference may include factors such as

the number of approaches, number of visits, duration of visits, time

spent huddling together, mating activity, and a variety of other

measures. Use of preference apparatus, in addition to allowing more

controlled investigation of particular factors (e.g., familiarity) than

may be available in seminatural apparatus, allows the experimenter to

control the degree of contact between choice animals and stimulus

animals. In a tether preference apparatus, for example, stimulus

animals are tethered in a fixed area while the choice animal Is allowed

free access to the apparatus and may express preference through










proximity or contact behaviors, or under appropriate conditions, mating

behavior (Ward et al., 1981; Huck & Banks, 1982; Webster, Williams, &

Dewsbury, 1982). An alternative method used in preference tests is to

place collars on the stimulus animals, and then place these animals in

compartments with doorways of a size large enough to allow access by

choice animals, but too small for the collared animals to pass through

(Mainardi, Marsan, & Pasquali, 1965; McDonald & Forslund, 1978).

Direct contact between choice animals and stimulus animals may also be

prevented by simply constructing stimulus compartments or containers so

that they are not accessible by the choice animal (Agren & Meyerson,

1977; Carmichael, 1980; Carr, Wylie, & Loeb, 1970; Murphy, 1977;

Webster, Sawrey, Williams, & Dewsbury, 1982). Experimenters have also

opted at times to test preference for odors from stimulus animals

rather than using the animals themselves (Carr et al., 1980; Fass,

Guterman, & Stevens, 1978; Gilder & Slater, 1978; Huck & Banks, 1979,

1980; Krames et al., 1967; Ruddy, 1980), or to restrict choice cues

to olfactory cues by using anesthetized stimulus animals (Landauer,

Banks, & Carter, 1977; Landauer, Seidenberg, & Santos, 1978; Murphy,

1980).

While preference apparatus offer the opportunity for greater

control over variables than do seminatural apparatus, the conditions

under which preference is assessed do not approximate natural

conditions as closely as do conditions in seminatural apparatus. With

preference apparatus, therefore, one may run a greater risk of

obtaining results that are misleading in respect to behavior under more

natural conditions. Social preferences may, for example, sometimes be










expressed less strongly in preference apparatus than they would be

In a more natural context; one might therefore be more likely to

falsely reject a factor as unimportant to social preference in these

tests. One way to minimize this problem is to first assess a species'

social behavior in more natural settings, such as in seminatural

apparatus, and select factors for preference experiments on the basis

of those results. Alternatively one might use results from seminatural

experiments in part as a guide in interpretation of results from

preference experiments.

General Experimental Information

This study was designed to provide data on aggression and

familiarity as factors in the social preference of monogamous and

polygamous species. Partial data are available about the function of

these factors in the social preference of the representative species

chosen for this study, P. polionotus and P. maniculatus.

Available evidence indicates that aggression may be an important

factor in the social behavior of P. maniculatus, that more aggressive

males may sire more offspring than less aggressive males, and that

differences in male aggressive ability may be important in female

choice in this species. In P. maniculatus blandus Blair and Howard

(1944) found that, in experimental populations consisting of two

individuals of each sex, one male would generally establish dominance

over the other. The dominant male generally nested with both females

more frequently than did the subordinate, and the authors were able to

establish (through coat-color markers) that dominant males sired the










majority (19 of 21) of litters in their study. Dewsbury (1979, 1981c)

found that male dominance in manlculatus balrdi was positively

related to copulatory behavior, and that dominant males not only

copulated more than subordinates, but that they also sired a larger

number of offspring (Dewsbury, 1981c). Elsenberg (1962) observed that

after the formation of dominance relationships between male P.

maniculatus gambelil, females of this species that had been paired with

subordinate males for two weeks prior to aggression tests generally

failed to remain with their subordinate male partners and nested

Instead with the dominant male.

Blair and Howard (1944) studied two subspecies of P. pollonotus,

P. pollonotus albifrons and P. pollonotus leucocephalus, and found

little evidence of aggression against conspeciflcs by individuals of

either sex. In addition all four individuals (two males and two

females) in a group were frequently found nesting together. From these

observations the authors concluded that PE pollonotus were a very

social species. Field observations, however, do not support the notion

that adult EL polionotus are highly social. Although E. pollonQtus

are commonly found in family groups composed of a male, a female, and

young (Blair, 1951; Foltz, 1979; Rand & Host, 1942; Smith, 1966;

personal observations), sexually mature Individuals of the same sex are

never (Smith, 1966), or very infrequently (Blair, 1951; Rand & Host,

1942) found together in the same nest. In addition Blair (1951)

observed wounding In some transient and immature Individuals and also

observed, in trap and release experiments, that adult females often

chased other females from nests. Smith (1967) has suggested that











females of this species "are normally dominant over their mates and

play a major role in the process of pair formation and maintenance of

the pair bond" (p. 236). P. polionotus have also been observed to

exhibit aggression in some laboratory tests (Garten, 1976; Smith,

Garten, & Ramesy, 1975), but the conditions for these tests do not

allow evaluation of the function of aggression in a social context, or

as a factor in social preference.

Few data are available on the function of aggression and

familiarity in the social behavior of P. polionotus, or in the

social behavior of monogamous species in general. The first set of

experiments in this study was designed to provide such data. These

experiments were conducted in a seminatural apparatus that was designed

with artificial burrows. This design takes into consideration the

semifossorial habits of P. polionotus, and thereby allows an

approximation of natural conditions in this species.

The seminatural experiments with P. polionotus were followed by

preference experiments on both P. polionotus and P. maniculatus.

These experiments allowed preference based on aggressive ability and

familiarity to be assessed under the same conditions for both species,

and thus allowed a direct comparison of the relative value of these

factors in the social preference of these two species. The first set

of these experiments examines aggressive ability and familiarity with

unrelated individuals (based on previous contact) as factors in social

preference; the second experiment examines preference for siblings.










General Methods

Subjects

Subjects for this study were 45 to 65 day old Individuals of two

species of muroid rodent, Peromyscus polionotus subgriseus and

Peromyscus maniculatus bairdi. The P. polionotus were laboratory-bred

animals one to four generations removed from the wild. The parental

stock was obtained from two different subpopulations in the Ocala

National Forest in Florida. The first group of these animals was

trapped in 1978 from road shoulders along State Road 316 between Salt

Springs and Eureka. Additional animals for breeding stock were trapped

in 1980 from road shoulders along U.S. Highway 19. These two

populations are from the same general area as that listed as population

25 by Selander, Smith, Suh, Johnson, and Gentry (1971). The method of

capture was similar to that detailed by Foltz (1979).

It is not possible to determine how many generations removed from

the wild the EP maniculatus were. This colony was founded at the

University of Florida with animals obtained from near East Lansing,

Michigan, In 1970, and additional wild stock has been added on several

occasions since.

Animals were housed In clear plastic cages measuring 48 x 27 x 13

cm or 29 x 19 x 13 cm with wood shavings as bedding. Purina laboratory

animal chow and water were provided ad lib. Prior to serving as

subjects all animals were maintained as litters. Peromyscus pollonotus

litters were weaned at 22 or 23 days of age, P. maniculatus were

weaned at 21 days of age. Animals that exhibited obvious physical











defects, such as extensive tail wounds or missing tails, were not

selected for study.

Animals of both species were maintained on a reversed 16L:8D

photoperiod. All adaptation and testing were conducted during the dark

portion of the photoperiod. With the exception of observations

conducted in the seminatural apparatus, which was in a separate room,

all studies and adaptation periods were conducted in the P. pollonotus

colony room. Procedural details specific to particular studies are

described in the methods sections of those studies.

Apparatus

SeminaturaJ apparatus

The seminatural apparatus was a large square Plexiglas arena 125

cm on a side and 46 cm deep. The sides of this arena were constructed

with 1/4 inch Plexiglas and the floor was constructed with 1/2 Inch

plywood and painted grey. The arena was partitioned, with four 85 cm

lengths of 1/4 inch Plexiglas, into a square central area that measured

85 cm on a side and four right angle triangular corner compartments

with sides of 85 cm, 61 cm, and 61 cm (See Figure 1).

Two nest boxes were attached to each corner compartment. Nest

boxes were constructed with sides of 1/4 inch Plexiglas and 1/4 inch

plywood backs. They measured 10 x 9 x 8 cm and had hinged Plexiglas

lids to provide access for removal of animals and cleaning. A 3.2 cm

diameter hole cut in the front of each nest box provided access for the

animals. In each corner compartment two matching 3.2 cm diameter

holes, cut in the sides of the apparatus, 45.5 cm from the corner and

1.5 cm from the floor, provided access to the nest boxes. The front of













































(0

S-
ra
CL
rc
0-..


r-




E
aj

r--




c:










one of the nest boxes for each corner compartment was connected with

silicon cement directly to the side of the apparatus in line with one

of these holes. The other nest box in each corner compartment was

connected to the second opening by means of a 48 cm length of Tygon

polyethylene tubing with an internal diameter of 2.5 cm and an external

diameter of 3.2 cm, and thus formed an artificial burrow. Silicon

cement was used to attach one side of the nest box to the apparatus and

to connect the tubing to the openings for the nest box and the

apparatus.

Animals could gain access from the corner compartments to the

central area of the apparatus through 3.2 cm diameter holes centered on

and 1.5 cm from the bottom of the partition which formed the

compartment. A 2.5 cm hole 3 cm from the right angle corner and 2 cm

from the floor of the apparatus provided access for the drinking tube

of a water bottle.

The seminatural apparatus was in a room separate from the colony

room but maintained on a 16L:8D photopericd identical to that

maintained in the colony room. The apparatus was illuminated in the

light phase of the photoperiod by four 75-watt incandescent-white bulbs

and two 60-watt red bulbs, each suspended three feet above the floor of

the apparatus, and during the dark phase of the photoperlcd by the two

60-watt red bulbs alone.

Behavioral measures were recorded by means of a 20-channel

Esterline-Angus event recorder. The behaviors exhibited by each group

of animals, during their four days in the semlnatural apparatus, were

also recorded on videotape using a Hitachi CCTV low light television










camera, and a Panasonic time lapse VTR video tape recorder set on a 72

hour record mode.

Preference apparatus

The preference apparatus was a three chambered rectangular box

with a hinged lid; It was constructed of 1/4 Inch Plexiglas and

measured 44 x 21.5 x 20 cm (Figure 2). The inside measurements of the

two end chambers were 10 x 21.5 x 20 cm. These chambers were open to

the central area through a 7 x 7 cm opening. The end chambers were

designed to accommodate small removable "choice chambers" which

measured 10 x 8 x 6 cm. A "stimulus box" with an inside measurement of

8 x 7 x 8 cm was attached to each end chamber, and was open to It

through a 6 x 5 cm opening. When choice chambers were placed in the

end chambers, therefore, one end of the choice chamber was accessible

from the central area, while the other end was open to the stimulus

box. A hardware cloth screen installed In the opening to the stimulus

box and a second three-sided piece of hardware cloth which fit the

inside of the stimulus box provided a "double screen" between the

choice chamber and the stimulus box.

A bank of three red-sensitive photocells (peak response at 735

nm), wired in a series behind each choice chamber, registered entries

to the chamber. The light sources for the photocells were 60-watt red

light bulbs placed 27 cm in front of the apparatus and directly in

front of the bank of photocells. Each photocell was attached to the

end of a tubular 4.3 cm piece cut from a 12 x 75 cm disposable plastic

culture tube. The outsides of these tubes were painted black; this in

effect columnated the light to the photocells. The photocells were

















uo O---- \































w



> L




























Un

w
LJ

F-,
0

I










situated such that in order to register a visit to the choice chamber,

an animal had to be completely Inside the chamber, and at least

partially in the half of the chamber closest to the stimulus animal.

Each bank of photocells was wired In a series with the coil circuit of

a 10,000 ohm, 24 VDC DPDT relay (see Figure 3). These relays were

powered through output from a variable power supply set for a

continuous output of 26 volts. One of the normally closed circuits of

each of these relays was wired into the pen circuit of an Esterline-

Angus event recorder; this provided a permanent record of entries into

each choice chamber. Output from another normally closed circuit of

these relays was used to control a second set of relays on a relay

rack. Two banks of Sodeco counters received input through the normally

open contacts of these relays. The first bank of counters was wired in

a series to pulse former and recorded the number of visits to each

chamber regardless of visit duration. Input to the second bank of

counters was regulated by means of a recycling timer set to produce

pulses at 1/3 of a second. These counters recorded the total duration

of visits to the nearest 1/3 of a second. Session duration was

automatically controlled via another timer (not displayed) which

controlled the input to the recycling timer and counters.

Aggression apparatus

The "aggression arena" was constructed from a large 48.5 x 38

x 20 cm plastic cage. Two 3.2 cm diameter holes were cut in the two

longer sides of the cage centered 25.5 cm apart and 3.5 cm from the

bottom. Silicon cement was used to form a gasket around each hole.

Matching holes and gaskets were placed on one side of two 48 x 27 x 13










cm plastic cages. The larger cage and two smaller cages could then be

connected by 6.5 cm lengths of Tygon polyethylene tubing (Internal

diameter of 2.5 cm and external diameter of 3.2 cm) to form the

"aggression apparatus" (See Figure 4). During adaptation procedures

the aggression arena and smaller cages were connected with unobstructed

lengths of tubing; a piece of metal screen in the center of each

length of tubing prevented animals from traveling through the tubes

during tests. A 1/4 Inch 53.5 x 43 cm Plexiglas lid was placed over

the large cage, and wire cage lids over the smaller cages, while

testing was conducted.
























































FIGURE 4 Aggression Apparatus














SECTION III
EXPERIMENTS

Seminatural Experiments

This section is divided into three major subsections; the three

sets of experiments that comprise this study are each described within

separate subsections under the headings of Seminatural Experiments,

Aggression and Familiarity Preference Tests, and Sibling Preference

Tests. Each of these subsections begins with a brief introduction to

the experiments in that subsection, and specific information on

subjects and procedures for these experiments. This information is

followed by the results of these experiments and a brief discussion of

the results. The results of all three sets of experiments in this

study are discussed together, in the context of the ecology of EP

polionotus and P. maniculatus and theoretical considerations, in the

General Discussion section.

Introduction

This experiment was designed to provide information on aggression

and familiarity as factors in the social behavior and mate selection of

E. polionotus. (Similiar types of data already exist for P.

maniculatus: Blair & Howard, 1944; Dewsbury, 1979, 1981c: Elsenberg,

1962.) Although it is difficult to establish the relevance of factors

in social preference per se with seminatural observations, such data

can provide an indication of the functions a factor may serve in










nature, and can provide Indications of whether a factor may be of

importance in social preference.

Subjects

Subjects were 40 male and 40 female LP. pollonotus. Prior to

serving as subjects, animals were maintained as previously described in

the section on general methods. Subjects were selected using the

criteria described in the general methods, and the additional criterion

that the animals within any group had no common grandparents.

Procedure

In order to better separate and evaluate the roles of aggression

and familiarity in the social behavior of P. polIonotus animals were

observed under two different experimental conditions, the "paired"

condition and the "single" condition. Twenty animals of each sex were

assigned to either the single condition or the paired condition.

Animals In each condition were divided into 10 groups; two animals of

each sex were assigned to each group. Each of the 10 groups of animals

in each condition, single or paired, were treated separately. Animals

within each group were lightly anesthetized with ether and shaved In

one of the following four patterns: (1) band shaved around the neck;

(2) band shaved around the middle; (3) band shaved at the rear; (4)

no shaved area. Shaving was performed one day prior to beginning the

first experimental manipulation. Approximately equal numbers of males

and females received each shave pattern. Subjects under both the

single and paired conditions were exposed to a series of three

different experimental manipulations. These manipulations, in order,










and their durations were "nest building," 4 days; seminaturall

isolation," 3 days; and seminaturall interaction," 4 days.

During the four-day nest building period animals were housed in 48

x 27 x 13 cm plastic cages on San-i-cel bedding. Animals in the single

groups were housed individually; animals in the paired groups were

housed as two separate pairs of opposite-sexed animals. Three 2-inch

square "Nestlets" (Ancare Corp.) were provided as nesting material in

each cage. The type of nest built was assessed just prior to the

beginning of the dark period on the next 4 consecutive days. Nests

were rated as one of three types: (0) no nest; (1) platform nest;

(2) covered nest.

The seminatural isolation period began in the first dark phase

which followed the nest building period. Animals were transferred from

the colony room to the room containing the seminatural apparatus

approximately 15 min after the beginning of the dark phase. Animals

from single groups were each placed individually in corner

compartments, with animals of the same sex in compartments diagonally

opposite each other. Animals from paired groups, which had been

maintained as pairs during nest building, were transferred to the

seminatural apparatus in the same paired relationship. Pairs were

placed in corner compartments of the apparatus diagonally opposite each

other. The opening from each corner compartment to the central area

was closed with a solid black rubber stopper so that animals were

restricted to the compartment in which they had been placed. The floor

of the central area and of the corner compartments had been covered

with San-i-cel to a depth of approximately 1.5 cm; each corner










compartment also contained three Nestlets, and food and water was

available ad lib.

Animals were maintained in the corner compartments for 3 days.

Activity during this entire period was videotaped. Each pair of

animals in the paired groups was also observed for three alternate

10-minute periods during the dark phase on the day the animals were

Introduced, and on the following two days. On the first day,

observation was begun as soon as all animals had been placed in the

apparatus. On each of the following 2 days one of the pairs was

designated as the first pair to be observed, and the first period of

observation was begun when the members of that pair had emerged from

their burrow. The behavioral and aggressive measures that were

recorded were similar to categories described by Allin and Banks (1968)

and Colvin (1973). Measures were recorded by means of a 20-channel

Esterllne-Angus event recorder. The measures, and definitions of each,

were as follows:

Approach Scored when an animal came within one and
one-half body lengths of another while
oriented toward it.


Attack Scored when one animal lunged at or charged
another but did not pursue the other or
initiate vigorous biting behavior. This
behavior could be accompanied by a single
bite or attempts to bite.


Scored when one animal pursued another.


Chase










Fight


Rough-and
Tumble-Fight




Displacement



Submissive








Aggressive
Digging


Scored when one animal's attack on another
escalated to vigorous biting behavior by
both individuals. Generally the initiator
would knock the other animal over, or roll
to one side with the other animal clenched
in its jaws while shaking its head, often
simultaneously clawing with the rear claws.
Fighting often resulted after one animal did
not retreat when attacked, but rather attempted
to defend itself or at the end of a chase if
the pursuing animal caught the other.


A very vigorous form of fighting; rough-and-
tumble fights were only scored when both
animals were tumbling end over end while
attempting to bite and claw each other.


Scored when one animal retreated upon
another animals approach.


Scored when one animal, upon approach or
attack by another, either rolled over on its
back, or reared back upon its hind legs with
its nose pointed up, and made no attempt to
defend Itself. Both approach and submission
or attack and submission were scored for each
encounter.


This was a very vigorous form of digging
behavior much more Intense than the type of
digging these animals have been observed to
perform in an isolated test (Webster, Williams,
Owens, Geiger, and Dewsbury; 1981). Although
this behavior was not generally directed toward
an opponent, it was very similar to that described
by Allin and Banks (1968).


Under both experimental conditions, single and paired, the

isolation period was followed by the seminatural interaction period.

Ten min prior to the first dark phase in this period the rubber

stoppers were removed from the partitions between each corner

compartment and the central area. Behavioral and aggressive










interactions between animals, as defined above, were recorded during

the first hour of the dark phase for 4 consecutive days. Nesting

relationships were recorded each day, for the last 3 of these 4 days,

20 min prior to the beginning of the dark phase. An animal was defined

as having nested with another if it was found in the same nest with the

other, and videotape records verified that it had not switched nests

between the period extending from after the first 1/2 hr of the

preceding light phase to 1/2 hr prior to the nest check. Activity

during the entire isolation and interaction stages was videotaped.

The seminatural apparatus, including the artificial burrows

and nest boxes, was thoroughly cleaned with a solution of Sterigent (a

deodorant and disinfectant soap) before each group of animals was

introduced to the apparatus. Water bottles were also cleaned and

refilled, and fresh San-i-cel, food, and Nestlets were placed in the

apparatus.

Results

Peromyscus polionotus appeared to adapt very quickly to the

seminatural apparatus in general, and to the artificial burrows in

particular. All but five of the 40 individuals in the paired condition

entered and explored the artificial burrows within the first hour of

observation, and all except two pairs of the 20 pairs observed in the

paired condition had constructed at leat a rudimentary nest in the

burrow by the end of their first day in the apparatus. Individuals in

the paired or single groups were only infrequently observed nesting in

the alternate nest box, although this box was frequently used for

feeding and as an escape when individuals were attacked. Aggressive










relationships between Individuals in each group appeared to remain

fairly stable over their four days together In the seminatural

apparatus. In all 10 single groups, and in seven of the 10 paired

groups, the individual with the highest total frequency of aggressive

behavior (sum of all attacks, chases, fights, and rough-and-tumble

fights) on day one, still exhibited the highest frequency of aggressive

behavior on day four. In the other three paired groups the individual

that exhibited the highest frequency of aggressive behavior on day two

also exhibited the highest frequency on day four.

Each animal in a group could potentially interact with twice as

many opposite-sexed individuals as same-sexed individuals. To adjust

for this bias, the mean value of any measure of an animal's interaction

with both opposite-sexed individuals, rather than the total, was used

in analyses Involving opposite-sexed Individuals.

Several significant differences In aggression were apparent in

comparisons between males and females in both the paired and single

conditions. Males were more aggressive than females in a statistically

significant larger number of groups by all measures except the number

of rough-and-tumble fights (designated in tables as r&t fights; see

Table 1). Within the single condition males were the more aggressive

sex in a significantly larger number of groups by all measures except

the number of rough-and-tumble fights and the duration of

rough-and-tumble fights. Within the paired condition males were the

more aggressive sex In a significantly larger number of groups for the

measures of number of attacks, number of fights, duration of fights and

number of approaches. There was no measure, for either the paired or











Table 1

Comparison of the Number of Groups In Which
Males or Females Were More Aggressive


Total (N=20) Paired (N=10) Single (N=10)

Measure Male Female Male Female Male Female

No. of attacks 19 1*** 9 1* 10 0**
No. of fights 17 2*** 9 1* 8 1*
Duration of fights 18 2*** 9 1* 9 1*
No. of chases 17 3** 8 2 8 1*
Duration of chases 17 3** 8 2 9 1*
No. of r&t fights 13 5 6 2 7 3
Duration of r&t fights 15 3** 8 2 7 1
No. of approaches 19 1*** 10 0** 9 1*
No. of displacements 15 4* 7 3 8 1*




All durations are in seconds.
Sign test 2-tail *-<.05 **p<.01 ***q<.001










single condition, for which females were more aggressive than males in

a larger number of groups.

Males in general also exhibited higher total levels of aggression

than females by all measures (see Table 2). Males, in both single and

paired groups, exhibited a higher frequency of attacks, fights, chases,

displacements and approaches than females. They also exhibited longer

durations of chases and fights than females in both types of groups

(see Table 3). Although differences in the total amount of submissive

behavior exhibited by males and females across both groups were not

statistically significant (1=1.28, df=19, p>.05),males had more

submissive behavior directed toward them than did females

(paired-=2.71, df=19, p<.05).

Because aggressive digging was not immediately recognized as a

possible correlate of aggression, it was not recorded for the three

Initial paired groups. It was recorded for all subsequent paired and

all single groups. No significant differences in the frequency,

duration, or mean duration of aggressive digging were apparent in

comparisons between paired and single animals. Males displayed higher

levels on all of these measures than did females, with the exception of

the comparison of the average duration of aggressive digging for single

animals. High-aggression males (those in each group with the highest

total frequency of aggressive behavior) displayed a higher frequency of

aggressive digging than low-aggression males (paired-=2.30, df=16,

p<.05). The difference between high and low-aggression animals in the

level of aggressive digging they displayed may be due In part to

differences in the response of these two classes of individuals to











Table 2

Comparison of Total Aggression Within Groups by Males
and by Females In Both Paired and Single Conditions


Male Female

Measure Mean (SE) Mean (SE) t

No. of attacks 46.30 5.95 10.20 2.41 5.23****
No. of fights 14.55 2.24 3.05 1.07 4.23****
Duration of fights 23.00 3.96 4.60 1.46 4.31****
No. of chases 116.20 12.18 21.85 5.51 5.98****
Duration of chase 679.10 79.01 128.40 32.79 5.59****
No. of r&t fights 5.00 1.44 1.25 .42 2.60*
Duration of r&t fights 10.30 3.04 2.80 1.39 2.35*
No. of approaches 64.10 7.91 23.40 3.61 5.62****
No. of displacements 12.80 2.59 3.40 .90 3.43***




All durations are In seconds.
Paired -test df=19 2-tail *P<.05 ***,<.01
****D<.001





















se a
Oh *5 *
Ul.CNl' r mN~Imrtrh-- *
~nm.0On'a'or-0-

C~~for-tO hooO h-^'M'~r-.aoh.
.- o -CP itno'on
0 4





E n
0 C4 In 4
L.



Q ONV C
o z -1 0 a 4 W o
V)
nI



C -. '^*^or.0 Mr~0 vr -0)
uW ON|0N.0
( i *1 *a 0 1 0 w I Z,
W- W N nI 10 .5T nn )0 r- wt o


z ooocoomp0Oh00-0ow
C r-ON.0Or-uOlfs.Or.K5.TOO.
L" I a'0^ 'aa""'0 'a s "




5 *: N '-N
n*






N &U asC140 a 50
tnn





D S/) N; 4 *h 4- N
-y o
LL
0 co r ww '00 0








0 tm a v -nn0a .00
c. 10 N 0 n C- w N6"Wr4 CO t
0)O .-o 0tr-.5 .O0N 0 0 ; 0 n
(A 00A 'o 0 '-0'o





QC) C L
o a
S_ Wa).. S N 3O In 4-oInP0C)^io
SN 0 -
0 C %0a0
a) c ccirmioK ri s*










1 u Es as a 0 aOr
.0 10 *55 Se a e* LL.
U01 VI (0m0~10N C









C-4 N Wnn~~-
s ^cn ^n no -:: ?our





see' Ce easemsrri *c on r-Unn a..0'.r..5-

fQ H. N-^ -,- -








0 I N r- CN 1
in







CC
4- .- 4














a0


0 r
a~ l cc
0x A 0 c 0 0 )0 10 r0 10









^.^~~ ~ 0, 2 0-**** *-
^4.L Na V) A500N .*
Q) f V




o1 5 S N -N 5-N U 4
t10 a a 0o


I- a*,

UL U LO
CC 0-0 LA O)I I ) 0 fl










0 .S N L" N0 00

X X X
aa
o c: n^csm-- irsir- m-OO^t N I I







0 M^.--ow^Nf\- (


.0
a S
4-a
Q+- -f > XN |
a=+- 0 C
a- a o c -a
(A a 4- 0)0) l
+- wo < i-a- ,
a Un L. C


a'* U C~5 0
o*- o..-+-0o- e >o'-
o ox: oCS- o0 *
iOcaOc:- c ioo c
U+--0OS0O-O00- 0- c
(Qr:--- 1f +- ^Ql-- 4- L ~- 0.*-
+i- aa.- 'o -a 04- -5- aw- 0)0- o -0
** oI.







00- 0- 0- 000-
as as SC C|
.- ta .-a. .-aC)
:z-1zr ac H ~o
oaO~ oOSOCOOO
i-IZI- ZZCb-










noises within the apparatus. High-aggression animals often

Investigated noises made by other Individuals In the apparatus.

Low-aggression Individuals generally Ignored these noises or retreated

from them. Low-aggression individuals that attempted to dig,

therefore, In effect increased the probability of attack by

high-aggression Individuals, whereas high aggression Individuals dug

without Interference.

Individuals directed more aggression toward same-sex than

opposite-sex Individuals In both the paired and single conditions (see

Tables 4 and 5). Males in both single and paired groups directed more

fights and rough-and-tumble fights, and longer durations of these

behaviors, against other males than against females. Females in both

single and paired groups directed more attacks toward same-sexed than

opposite-sexed Individuals. Males and females in both types of groups

directed more chases toward same-sex than opposite-sex individuals.

Although many of the differences in aggression between sexes were

significant, and many significant differences were also found in the

level of aggression directed at same versus opposite-sexed Individuals,

the overall levels of aggression displayed by animals in the single and

paired conditions were very similar (means and standard errors were

presented in Table 3). Animals In the two conditions displayed

significant differences on only two of the aggressive measures: paired

animals displayed longer average durations of fights with same-sexed

Individuals and a greater number of approaches to same-sexed

Individuals than did animals in the single condition (=2.12, df=78,

p<.05; and =2.10, dL=78, .<.05 respectively).



















*

19 0 )CM M- n U9 91 00% r




Ln mr C4- nn L- 1

0 f 0tooo %Cm D 4m0a


a C w- C3 %0
VN 00 0




IN
e o
-00


cE ooCmOin i O o
a P '0 (4o(o0 r





0 P n X '









4 S


x NM MCCDo Cnnon n
L 0
o a



0 IC N 4- 4
0 -
















-- E k CO-N CD aLn n n r-C9x v
CI) co c m o o
)* *




















o cnn w N o t re C
nE .n fn MCI
Sa m o o o o o o o o ir f
-) N1 N --5





















m cn
a v -N m N -o co An0 mI 0 U)


0n 0













IA. 0
V) 0 E In n4DO.D W'n *o















i- 4O a O e
0 -30 (





SC 0 0in














us U L c IA
E X
(0 10 J-_ 4*)















(n O* O o
u --4000 a-







to) c- o




-- -2' l0s-h
o 0 0%
m z Ez%' M07 3a
0 -. '0 ( Nr.%la

o o.



U) (U C L0 C 0O Iu '







S00 0 ) 0 3 O












3-l Z O '.0-Z <00










48










**
rn 0m w' 0N N 0Mtn 0 on in

N-o NN

(0n- U'oPmmoUoPo
Cd,
4- o
(n









to c
V 0 ifa W! Ci -W! ci Ci
0
S0 0 .. ..










0 *



0): 0 C PO C4I WN Wo o'
l) X 0 O O6- C4T4 in
Z | O C O CD CDWM %w C3M



0 %( aW % C o Nn O



0

0 0 +U 0- *% U
Ln 10 a tn a. C) Fn t v Cl- 0
a ) V










C4






ou
0 _


06 4 -W* N






QO -- l 06


-* 01 0'0mI0%-in o 'I ri n








4n
X ** x











ou &C o-- o0
| *r *0 C










4 0 c 0. 0-
2_ U C L CM C Lo(










0-


L- m o cL!




0l >0 z I M
0 in+-0 000

In u 00 El-



in I- C c uincLC (A
2. ZZSQZQZ <0










Comparisons of aggressive measures between the two conditions

within each sex yielded significant differences for females only (means

and standard errors were presented in Tables 4 and 5). Paired females

exhibited a greater number of approaches to same-sex Individuals and a

greater number of displacements of same-sex individuals than did single

females (=2.57, df=38, p<.02; and =2.08, d=38, p<.05,

respectively).

The various measures of aggression recorded tended to be

correlated with each other. The total frequency of attacks, chases,

fights, and rough-and-tumble fights were correlated within each sex for

both paired and single groups, as were the duration of chases, fights,

and rough-and-tumble fights. The frequency of approaches was

correlated with the number of chases for males and females in both

conditions and with the number of attacks for paired males and females

and single males (see Table 6). The amount of submissive behavior

directed toward single females was correlated with the frequency and

duration of fights (Pearson correlation, r=.724 and =.798,

respectively, p<.001) and the frequency and duration of rough-and-

tumble fights (Pearson correlation, =.704 and .800, respectively,

p<.001). Submission was also correlated with the total frequency of

approaches for paired females and single males (Pearson correlation,

=.444 and =.515, respectively, p<.05). Frequency of aggressive

digging was correlated with the total frequency of aggressive behavior

(combined frequencies of attacks, fights, chases, and rough-and-tumble

fights) for paired males and females (L=.638, .<.05, and =.845, p<.001

respectively) and single males (=.697, p<.001). Duration of































-- *KI


(- %.


L*

(N co
QIo
* *
0)0)


* **



K *2
* *



couir-=
r- r-


*
**
*



***





*** *


r- rC CO o0
r~ ~ o c
* *


* *








**2*
2Kr *2T CM





to l co




COCOr C


*
*
*
**

*-k0** <
C-'0-CMN
N3 0 N N


*
*% *
***
r~ OK o

e>M 0 oenee



*
*

\o n- co
OC NM n


*
2K
*K


* ***
2K **2K
* ***
* *2*

coCM T M I %0 "r co r- r-


*2**

***
***

or- r- N)
* e *


**
*2*
*2*
*2*
0% m IM
\) 00 00
o co c


*2K
*2*
*2K
*2K


NM r r- 0o
* *


*2
**
*2*
*2*

'00)




*2*
*2*
*2*
*2*


CM co


K ***
IK *e
K **2**
7' co co 0 oro 0
)N %0 N 'o r- n Ln


U)



0Q

L







O
0

aCD
- O

0 L




L





CO
L
o c
Sow

+-CO




0I


0 0
0-


L
00
L (0
0 )0


nL

+- l
(c
D
t(


U)a) U)

4- U) U)0)EE E c

u C)nD) C CUUUW--
-0(D E U) n (D ) U) ) CO(O (O4-'4-4-
-C (D -- ( E 4-) EO--
)00 U CC= a=)CD C = D L L C7)+- 4-
U) -- (0 (0 0)U U 0)u u a.U)n U- x3od
(1)4- 4- 0 U 0 (u (U (0 a.- L L
ui)C I- L.0)C- 0 4- 0 MDOvo
C O0)4- L.U U) La. L "a0v 0V
S- o4a .- C 4- .n U) 4-0 U)-n o C C c
U S- L (C 0 .C U (oD i 1 0 (0 ( 4c

CO O C CO c C c C Co C 4-4- c0 Un nu)
CO O CO 0 CO C .C .CC O

( U0 U 4-4-4-4- ) ) )-- 0

4-4-4-4-4- 0 00 0) 4-4- 0.0 0 0
4-4-4-4-4-- --_-__-C .dod Q.
M CO C0 C0 C4 4- '4- U i- LL C C C C
000

000000000000000-4-4-
............... L L L
;0000200000000000 n


SCo
00

+- v


U 0
















-0 *
cV









C













- O
0
L










.+-
Io
C- CI
i- oC
00*
0) 4-z
U)
c
c 0



0 (C-
--0


L I
t-r





-0 II
< ozt


1
:#

C
C
r










aggressive digging was correlated with total frequency of aggressive

behavior for single males (r=.527, .<.05) and paired females (r=.845,

.<.001). An animal's weight did not appear to be an important factor

in aggressive Interactions. Only the correlation between weight and

the frequency of rough-and-tumble fights In single females was

statistically significant (r=.378, p<.05).

For paired groups comparisons were also made between the level of

aggressive behavior that occurred while pairs were confined to the

corner compartments and the level after access to the entire apparatus

was allowed. Very few aggressive interactions of any type (chases,

fights, attacks, rough-and-tumble fights) were observed between pair

members during the period pairs were confined to the corner

compartments (Mean total frequency of aggressive interaction per paired

Individual=.20, range = 0 4.0). Therefore only the total frequency

of aggressive behavior, rather than the frequency of behavior In each

category, was used for comparison.

The total frequency of all aggressive Interactions (attacks,

fights, rough-and-tumble fights, and chases) between pair members while

confined to the corner compartments was not useful In predicting

frequency of later aggressive interactions with pair members

(males:r=.034, .>.05; females: r=.087, p>.05) or total frequency of

aggressive Interactions (males: =.015, p>.05; females: r=.118,

p>.05).

Pairing did, however, have some effects on later levels of

aggression. Males in paired groups were less aggressive to the females

with which they had previously been paired than to females with which










they had not been paired by the measures of frequency and duration of

chases (one-tall palred-=2.18 and 2.22, respectively, df=19, P<.05).

Males also exhibited a higher frequency of approach to females with

which they had been paired (one-tail paired-=1.78, df=19, p<.05).

None of these comparisons were significant for females (Number and

duration of chases, =.38 and .76 respectively, approach; =1.08,

df=19, P>.05).

A problem arises when one attempts to compare different classes of

animals as to their levels of aggressive interactions with one another.

The problem is that the total amount of contact between different

classes of animals may vary. For example, If females tend to avoid

other animals, but males do not, Individuals would have more

opportunities to be aggressive to males than to females. A difference,

therefore, in the level of aggression an individual expresses toward

Individuals of one class versus another may reflect a true difference

in the frequency of aggression, or a difference in the frequency of

access to Individuals of the two classes. One method of gaining a

clearer understanding of the level of aggression, and differences in it

between classes of individuals, Is to construct a scale or index for

comparisons which accounts for differences In frequency of contact.

An "aggressive Index" was calculated for this study by dividing

the total frequency of all aggressive encounters initiated by an animal

(frequency of attacks, chases, fights, and rough-and-tumble fights)

toward any other class of individuals by the total number of contacts

initiated by that animal toward that class of Individuals (total

aggressive encounters plus the frequency of approaches and










displacements). Although there may be qualitative differences in

approaches which elicit displacement or submission and those which do

not (for example an aggressive individual may signal its status through

adopting a particular posture), no means was available in the present

study to detect these cues. Therefore displacements or approaches with

submission were classed as contacts without aggression for purposes of

constructing the index.

No significant differences were apparent between paired and single

groups, or in comparisons between males or females of these groups, in

the total frequency of contacts or the frequency of contact with

same-sexed or opposite-sexed individuals (see Talbe 7). Single females

did, however, have a significantly higher overall aggressive index

(frequency of all aggressive behaviors divided by frequency of all

contacts) and a higher aggressive index against opposite-sexed

individuals than paired females.

The total frequency of contact was significantly higher for males

than for females in the paired and single conditions. Although the

overall aggressive index was significantly higher for paired males than

paired females, the difference between single males and females was not

significant (see Table 8).

Paired males and females and single males all displayed a

significantly higher frequency of contact with same-sexed than

opposite-sexed individuals. Whereas both paired males and females

displayed a significantly higher aggressive index against same-sexed

than against opposite-sexed individuals, this comparison was not

significant for single males or females (see Table 9). Paired males,

























o4- C o


!D Go %0 04 r
(N (N -






S0 C O W % CM e l
E -W 1l 0C -T




00 000 cn

L

S* *0-0
ocn





C% 4
Q)% wo WN




SOO




a> a -
U O 0O'.c
rt-c 000 o o"o


00 c 1 1!




C






t C+ C C O

4-) t/c 9,4 ^ -

C 0 U) -C
0 a
E0 irn r o o oo






4- ll4-







X0 C in%-(N-
I 0i)
c 0 3 4 )
0) V) C C a .oc.4C















M_4-
0 o-

4- a: _0 4- S

00 0- %0 10


a) I) % -
> 0I












a)0 V 3 ,
S U) 00 0 0













4- -D ~ 4E -0
0 0)










O 0) L N. co




























o
*
S
o0%
0- 0^
1- 0



0^0

%0



UN
N 0




oo


N

C)


%00

f-
04
* *
0%

K> 0
N0 -

'n
oN


01C

Nt 0






~0%


Lf
a)


E
()
LL-











-0
cc
IA


C4


S.-
0
4-



t

cD


















Ln
a) 4-
0
-o






-u



5-


-e




a)












en
en,
<=C


0














"o














CD


o-





















U,
01













c


*o
c
a)














0
0o




C

0
o-
to


w
a) V

E
4)
u- a
(0
(D



LAJ
LtL C
a)



w
U)














CD
au


a)



00































4)
N

c:


L-



U)































m
la

a)
(D
aM
LU

a) -

a)
C



a)
a)







LU-
0)












to
(a
s









ICD



a)
In


u.



CD W






10

CD
u ) c






(0




a)
L
UJl









a)
a)



U1
10
10
S.


- Un
Ch co







14
* *
* S
* *
* *
-n o





o co










o I
o


10




U'
O




O <
OX -

> o|


to -
o ro


0
0
o
o

v
*
*l
*x


0
U
C
tO
L














































U')

(0






0- -0





uw
r= o

I




,I- 0
-o o

>)



,-O
0-






0c,





r r-









t a_


r(
%L~


x
0 -
U)1 U.)
I U)
0)
--
M

0 C
0. (0
0 S


x
I Q )
0 -
4-

0 C




x w




E
0 C
010
a,


*
0% o
%0 0
C M

1o r-
o o





CN
-'0





oo r-
%0 0A














CM!1
Dm


*
*
*
*
r'%'0

l n
r-L

'0 u0




0o


o r-~



00


0>-
1 0)
0-
10 U)


3C
- 0%

N -


N -








NO -
LA n









't

c c
N N

N N
D 00




o o
0 C4




P%

r- \


00
0 0!


*n


**











0%00

N -

N en
N 0
o o









0f-





L 4n
S-c


0M-


0
0





V



4t
















LA
0




0
0








Ln
0
V






10 -



















( 0
E--
>1




x
0 0%




0-
0a.

U-
I-

0
In
00
3-0



C








04-








+-I


0Q -










but not paired females, exhibited a lower aggressive index against pair

members than against opposite-sexed non-pair member (two-tail I-test,

df=19, males and females respectively: =2.25, p<.05; t=1.41, p>.05).

The frequency of nesting arrangements, for days on which complete

nest data were available, is presented in Table 10. It is of interest

that two animals of the same sex nested together only once without an

opposite-sexed animal also present. Animals nested as two opposite-

sexed pairs on over 1/3 of the days for which data were available and

almost another 1/4 of the nesting arrangements observed included one

opposite-sexed pair.

Only data on nesting behavior for days on which nesting

relationships were known for all individuals in a group were analyzed

statistically. Nest data were available for all but one paired and one

single group. Three days of nest data (the total possible) were

available for two of these nine paired, and seven of these nine single

groups. Two days of data were available for six paired and two single

groups, and only one day of data was available for one of the paired

groups. The mean number of days of data available for nine paired and

nine single groups were 2.11 days and 2.78 days, respectively.

The analyses of nesting behavior presented in the tables are based

on the "Wilcoxon-test" (Siegel, 1956). Analysis of nesting behavior by

this test in the present study may give more "weight" to observations

from groups for which more days of data are available. Significant

comparisons in the tables that were not also significant by the "sign-

test" (Siegel, 1956) are noted in text. Animals generally nested with

opposite-sexed rather than same-sexed animals. Differences in nesting











Table 10

Frequency of all Possible Nesting Arrangements


Paired Single
Total Groups Groups

All four together 4 1 3
Two opposite-sex pairs 15 7 8
Two males, one female 3 3 0
Two females, one male 6 4 2
Two males 0 0 0
Two females 1 1 0
One opposite-sex pair 12 2 10
None together 3 1 2




Only days on which all animals could be accounted for are included
(Total number of days=44).










59
























z r--

N W -
mxu
0 C O -r O




0 a) cCOM-




IW -C'
a u -




L m

-rC EX 4
-a 1 1 I *





*x a












0.0) c o x
() a 0rV (







0 0 )
i~o- o -

4Z-Z
U) a)- -I C o
oi 4- U 0
> t 0








0E X C-



kn t
0 N C nar- X v
0. L* Il *


w 0 0 U
EU 0










U U Ut *0












-- s -s s
ON I) 0-




zz an N e
CCD V

-CD t



go ODU 4
C" Q


LL- x r O)0
00L C0 -o C
0)r +- ID C.
0 5 -D
CO *









) U E 4 *I








,A 0 -
EX C r- C











inU 0
oC Ic I -




)4- Q) C 00
IOIDON I- -

1w wl 01 X *




















0 LO) 1 D = -
-EX cv-0













cn = 0.11
l..U) U)0o Zu
c ~ C_< /













































c
0
C'
ml

OS




SL

-




z


01

o -
w

'U





IL C
0 3



c) w








I -
-wU



















31 t )
0)
am




C
0 -
w


.IL C



C
0 -

-w
0)

X L-


* *


CM (M

(M '*O IO







r- 0 0









- ?N 0
--o









' (s 0



r- N
(N -





\o in


K% 0











SCO M
- CM
















1 0 '0
* *







L. U







- 0- g
M -
* *






N- -1





t w- (



MN MN CN



an c



0)CC

C -0 0)
L 0)
ce


0-
< 0 (I)










frequency with same and opposite-sexed animals were significant for all

comparisons except paired animals in general, and paired females (see Table

11). (By the sign test the comparison for all females was also non-

significant, x=10). In general animals also nested with high-aggression

rather than low-aggression animals of the opposite sex (see Table 12). This

was true for animals in paired groups and single groups, and for males and

females. The finding of non-significance for comparisons within paired and

single groups, except single females, may be due to the small number of non-

tied observations available for comparison. (By the sign test comparisons

for paired animals and males in general were also non-significant, x=2 for

both comparisons). Total frequency of aggression was correlated with

frequency of nesting with opposite-sexed individuals for paired males and

single males (Pearson correlation, r=.710, p<.001 and r=.519, p_<.05

respectively) but not for paired or single females (r=.066 and r=.219

respectively, p>.05).

Animals did not nest more frequently with familiar individuals.

Comparisons based on all paired animals, males, or females were all

non-significant (Wilcoxon, N=number of non-tied observations: all

animals, N=24, z=1.24; males, N=10, z=1.22; females,

N=14, z=.60). Neither the number of days pairs had built nests

together during the nest building stage, nor the average type of nest

built, was correlated with nesting frequency with pair members (Pearson

correlation, nest days, r=.395; nest type, r=.250).

Discussion

These seminatural observations provide evidence that aggression is

likely to be an important factor in social interactions in P.










polionotus. As predicted of the behavior of monogamous species

(Klelman, 1977) frequent aggression was displayed by both males and

females, and the majority of aggressive behavior was directed against

same-sexed individuals. The suggestion that females of this species

are normally dominant over males (Smith, 1967) was not supported by the

results of the present study. Males displayed much higher levels of

aggression than did females, and females generally exhibited very low

levels of aggression toward males. In addition, high-aggression males

more frequently performed a behavior, aggressive digging, that could

function to display their aggressive status.

Although the frequencies of aggressive behaviors In paired and

single groups were very similar, the aggressive index indicated that

individuals In paired and single groups behaved differently.

Individuals in single groups did not appear to discriminate between the

targets of their aggression as well as paired individuals did.

Overall, the differences In aggressive behavior between paired and

single groups may Indicate a tendency for reduced aggression toward

opposite-sexed Individuals, especially pair members, in paired

Individuals. This is particularly true of paired males, which

displayed both reduced total frequencies of aggression and a lower

aggressive index, against females with which they had been paired than

against those with which they had not been paired.

Superior aggressive ability would appear to provide some social

benefits for individuals, as both males and females nested more

frequently with high-aggression rather than low-aggression individuals

of the opposite sex. On the other hand familiarity, although It










appeared to reduce aggression between pair members, did not have a

significant effect on nesting behavior. It would appear from these

observations that, in P. pollonotus, aggressive ability may be a more

potent factor in social preference than in familiarity. However,

because It is unlikely that Individuals under the present conditions

were always able to control who nested with them, It is probably best

to use caution in interpreting these results.

Aggression and Familiarity Preference Tests

Introduction

The results of the seminatural experiments Indicated that

aggression may be an important factor in social preference in P.

pollonotus, but cast some doubt on the importance of familiarity in the

social preference of this species. This experiment was designed to

test preference based on aggression and familiarity in P. pollonotus

and EL maniculatus in a more controlled manner, through the use of a

preference apparatus.

Subjects

Subjects were Individuals of two species of muroid rodents, fE

pollonotus and E. manculatus. A total of 40 animals of each species

served as subjects for aggressive tests and aggression preference

tests. Prior to serving as subjects, animals were maintained as

described in the general methods section. Within each species these

animals were each assigned to one of 10 groups, with two animals of

each sex per group. In addition to the criteria described in the

general methods section, no Individual within each group could be










related by more than two common grandparents to any other animal in the

group.

Following the aggression tests and aggression preference tests the

animals described above also served as "stimulus" animals for

familiarity preference tests, while an additional 40 animals, 20 of

each sex of each species, served as "choice" animals for these tests.

Procedure

Procedures were identical for each experimental group. Animals

for each group were separated from litter mates and individually housed

in 48 x 27 x 13 cm clear plastic cages. Peromyscus maniculatus were

moved from their colony room to the P. polionotus colony room. On the

following day, within the first 1/2 of the dark phase of the

photoperiod, animals were lightly anesthetized with ether and marked

for identification by shaving them in one of two patterns: either (1)

a band was shaved from around the neck area, or (2) a band was shaved

from around the middle of the animals. One animal of each sex was

shaved In each pattern. Animals were placed in 48 x 27 x 13 cm plastic

cages modified (as previously described under aggression apparatus) for

aggression testing.

All adaptation and testing were conducted during the dark portion

of the photoperlod. Animals were adapted to the preference apparatus

on the two days following the marking procedure. On the first of these

two days animals were adapted to the procedure that would be used when

they served as "choice" animals.

Adaptation to "choice" procedures was as follows: the animal was

placed In the start box for 5 min, followed by 1 hour free in the










apparatus without other animals present. Animals that did not exit the

start box within 1 1/2 min after the door was lifted were gently

prodded with the eraser end of a pencil, often simply lifting the lid

of the start box slightly provided sufficient stimulus for the animal

to leave the box. The same procedure was followed during tests.

The day following adaptation to choice procedures, animals were

adapted to "stimulus" conditions. Adaptation for stimulus animals

consisted of being placed In the stimulus boxes at either end of the

preference apparatus for 1 hour. Animals which were tested together as

stimulus animals for experimental tests were also adapted together.

During adaptation of stimulus animals for the aggression preference

tests an opposite-sexed pretestt" animal was allowed free in the

apparatus and its visits to either chamber recorded. This period was

designated as the pretest period. Each pretest choice animal had been

adapted to the apparatus previously, and served In several protests

with animals of the opposite sex.

Following adaptation to the preference apparatus animals were

adapted to the "aggression apparatus" for 2 hours on each of the next

three consecutive days. For these adaptation periods the animals home

cage was connected to the aggression arena by means of lengths of Tygon

tubing inserted into the holes cut in the sides of the home cage and

into the sides of the aggression arena. Animals were restricted to the

arena for the first 40 min of the 2 hr period by means of #6 black

rubber stoppers inserted in the ends of the connecting tubes. The

stoppers were removed for the remainder of the period so that the

animal had access to both the arena and its home cage.










Aggression tests were conducted on 3 consecutive days following

adaptation to the aggression apparatus. Males and females were

observed. Tests were conducted by placing the two shaved animals of

the same sex Into the aggression arena and observing them for 40 min.

Behavior during this period was categorized as approach, displacement,

aggressive, or submissive. Frequency of all aggressive behaviors

(total of all attacks, chases, and fights) was Included under one

category because aggressive behaviors other than attacks were extremely

infrequent.

Aggressive preference tests were conducted on the 2 days following

aggression tests. Two animals of one sex, that had been tested

together In the aggression tests, each served once as choice animals.

The two animals of the opposite sex, that had been tested together on

the aggression test, served as stimulus animals for both tests. Tests

were arranged by placing one of the same-sexed pair of stimulus animals

in each of the boxes at the ends of the preference apparatus 15 min

prior to the beginning of the test, and the choice animal In the start

box 10 min later. Tests were initiated by raising the door to the

start box, and thereby allowing the choice animal access to the

apparatus. Test duration was 1 hr, timed from when the choice animal

exited the start box. Order of testing was counterbalanced for sexes

across days. Although the stage of estrus was not controlled for in

these tests, smears were taken for each female after she had served as

a stimulus animal and on the following day.

On the day after the conclusion of aggression tests for a group,

the members of the group were each housed in a 29 x 19 x 13 cm plastic











cage with an Individual of the opposite sex. These "new" opposite-

sexed individuals had been adapted on the previous day to the apparatus

under the procedures described for choice animals. These animals each

served once as choice animals In the familiarity preference tests that

followed. Animals that had been paired for the aggression preference

tests also served together as stimulus animals for the familiarity

preference tests (The two same-sexed stimulus animals for each of these

tests were two Individuals that had been partners In tests for

aggression). This arrangement produced four tests for each group, two

tests for each same-sexed set of stimulus animals.

Smears were obtained from the females of each group prior to the

onset of the dark period on the seventh day after animals had been

paired. Tests were conducted with stimulus females only when both of

these females exhibited smears consisting of at least 75% leucocytes.

This type of smear would normally Indicate a nonreceptive state.

Females that displayed sperm on the smear were tested after they

displayed this type of smear. Choice females were tested individually

if they displayed smears with at least 75% leucocytes. Test procedures

for choice and stimulus animals were as described previously.

Results

Aggression Tests. The level of aggression (attacks, chases,

fights, and rough-and-tumble fights) displayed in the aggression tests

were very low. No aggressive behaviors were displayed in four of the

ten groups by females of either species. Peromyscus polionotus males

did not display aggression In two groups, while P. maniculatus males

did not display aggression In three groups. The comparison of total










values (for all three tests) for the four behavioral categories

recorded are displayed by sex for each species in Table 13. Only the

comparison of P. pollonotus males and females on frequency of

aggressive behavior was significant, with males displaying a higher

frequency of aggressive behaviors.

Because the frequency of aggression in these tests was very low

it was difficult to determine which animal of a pair was actually the

"most aggressive". Instead, the total frequency of approaches and

aggressive behaviors was used to provide an indication of which animal

of a pair might be more aggressive. This total frequency score,

although not an aggression score per se, does allow a comparison of the

tendency to initiate interactions or "assertiveness" of the two

Individuals in a pair. It would seem reasonable to expect that the

less timid of two individuals under these test conditions might also be

more likely to exhibit more aggression under other conditions. The

individual of a pair of animals in aggression tests that displayed the

greatest tendency to initiate Interactions will be termed the

"high-interaction" individual, while the individual that displayed the

lower tendency to interact will be termed the "low-interaction"

individual.

Aggression Preference. Table 14 presents data on the preferences

of animals of each sex for high or low-interaction Individuals of the

opposite-sex. No preference for high-interaction animals of the

opposite sex was displayed by P, pollonotus of either sex. Peromyscus

maniculatus males, however, did display significantly longer durations

of visits with high-interaction females than low-interaction females






























%o i co oC






CO C% U11%
a- in '0 0



0











C-4 I- r- o
CI
N Op







O' r- n 0







**,




.' N UN ..







4 -



N- c-
Umm-








r







C4 C4 ni




no tnLn o
o4 0 W 0
i mn -t
ac i o
'0NVr


O 4-
COC




LLOE
0 -

00--
L. L 0- E

<

ca
m =
su-
0 u



OO-







ca
co w
u
ro)





CO
0










0)0



aU



C0










oC
L)






a-


w
00









a,
ID






U-
00










UJ

E
0

















e
ID
C
10






















+-
LU.
C,)













0
40




C
'U
0
EE
0)
10

c




LL.
C
4D
w







a
0











































c
0

4-
30
00
0






L-
c






c
0


0 1
- l
Z 0>
4t-
c


C LU
0 I')
.2
Su
00 v

C C
0
0


c
0
4-
.c u
-L
SI0
4-
C


1 0 in
-I-~ 0






- w c
K> 01 0%








C 0%
-- N r







In 0 PI






-It
rr %





*o IN 0%

















LA0% CD
N























40
'0in 0%






















%tI0% 00
400 %






UcU
00














0n ocM
en







0% 0
ino K












.N

















0A 0 (D
ino co
-- 0






uiiO












C-4-
IA-
^n~t







I
mo r












0-
ijac
L 0
4- 0

o I- -Z


- rN 0%





o) 0% -

A CM 0%
N 0



CM4
o i-1 -
0C 00
0% in -
IA 0% N
N






M 0CN
N W% N



mIn -I
a> m f




C14


Ln Co C4

(A 04



o -







CO r- tU
0 CM CC)


o N N










C) in (A
In 0%k
in IA r-

CM IA M
m~-











IA


F' 0%
*t '0
^'0 0%
ON











000%
w0 00 Ia
0 0'0

N





'n
4- In
4-
In -




L.-
4- (
0> -
0
F5 *5
C

InOC














-4+- -
In 0 -
L- x

4- 0o
mc
4- <0
000
z \I-


c-
0


u L/)
o

(0
O




- 0)







S.- 4-)
4- 4-
0

I,,
C
Lno











E3- E
S0

Ia








"- -0
(0r
E a






4-
c> c












C 0
.) U
4-1














a.











and 16 of 20 males visited high-interaction more frequently than

low-interaction females (sign test, N=20, x=4, p<.01).

High-interaction P. maniculatus females and low-interaction P.

maniculatus males both displayed significantly longer durations of

visits with high rather than low-interaction animals of the opposite

sex (means for high-interaction females with high and low-interaction

animals = 1155 sec and 159 sec, one-tall paired-I: df=8, =2.37, means

for low-interaction males with high-interaction and low-interaction

animals = 1559 sec and 468 sec, one-tail paired-: df=9, =2.13;

p<.05 for both comparisons).

Although the stage of estrus for females in aggression tests was

not controlled, data were available for this factor. Comparisons of

male preference for high-interaction and low-interaction females were

made for these tests In which both stimulus individuals were In

diestrus (see Table 15). The only significant finding was a preference

by P. maniculatus males for high-interaction females by the measure of

duration of visits. This is also the only comparison which had been

significant when data from all females was included. Comparisons could

not be performed within the non-diestrous condition as there were no

cases for P. polionotus in which both stimulus females were

non-dietrous, and only two such cases for P. maniculatus females.

Comparisons of male preference for diestrous versus non-diestrous

high-interaction females and diestrous versus non-diestrous low-

interaction females are presented in Table 16. Peromyscus polionotus

males displayed more visits to non-dlestrous high-interaction females

than to diestrous high-interaction females, and P. maniculatus males












Table 15

Comparison of Male Preference for
High-Interaction and Low-Interaction
Females in Diestrus


High Low
Interaction Interaction

Measure Mean (SE) Mean (SE) t


F. polionotus

No. of visits
Total duration of visits
Mean duration of visits


e. maniculatus

No. of visits
Total duration of visits
Mean duration of visits


70.86
618.14
11.22


217.00
1291.28
71.55


11.41
152.07
2.75


187.73
510.14
48.03


76.00
419.60
8.47


17.50
114.94
6.32


16.18
115.14
2.54


3.85
61.94
2.36


.29
1.33
1.12


1.07
2.43*
1.37


All durations are in seconds.
Paired- EP. polionotus df=13
1-tall *D<.05


P, manlculatus df=5










73











n *




rn
m 4 0 %Q












O


(V-0-~~r
'tF co ot r-W W










E w


4,- Cr -
uo ro c o : K% r




0 C CDM i0n





0 0
0 40 A nz 90 0 0
g r.- i n




-o 0 -
0 0
So*
v0 SM M C *q-













rO C
I M W! W!- 9 9 '








4-4









03 X 000 0
v nc

'o 0 l CD -I 0 W%
E C Cll V C4











>>- >u
w Jw0 *D0
-- c0N 0
CD E %0 % Coo i J %-

QO vl c cIfolOflO0






+S- D- 0

Cn ri- U- CL C; 00"0






0 0 0-- g c


O 0000400




= >z >x 0
An nW u I

( c -0 0 > L-

Z 0- V (

(D 0 00 Q 1
=--z- 2-- 0





1i a^~ to E

























CO 0 CO


S% 0 co r co N



u 0% 10 -0 0% Im
4- -



o 2 % r. r


4-- o Mo>4
LA Z. lT K-N










Io








C3 O
OI









a 0 a w%






0- E er14 0 co C M




at LU a
; *o
(ULL +




0 a a a


0- Im A o0




o -

ro c ---L


0w 0 o -'O- '


S0 1





















cO
(r 9.s c- c K to>(Moo
4- 0 0 c* 4


0
"D. 0CM ~0-O
























'D A
03- -a g









c 4- -u O
'+D; --0- 0















xzo- x
4- 4-












Ca l B OO MCC









M UO OCC



X 2-1X '*










visited non-dlestrous low-Interaction females more frequently than

diestrous low-interaction females. All other comparisons of male

preference based on stage of estrus were non-significant. The stage of

estrus did not significantly affect female preference for high or

low-interaction males of either species (see Table 17).

Familiarity Preference. Male and female P. pollonotus did not

display preference for familiar individuals over unfamiliar individuals

of the opposite sex by any measure, although the comparison of the

total duration of visits did approach significance for females

(one-tall paired-, df=19, =1.47, p=.054). Peromyscus maniculatus

males and females displayed significantly more visits to familiar than

to unfamiliar individuals of the opposite sex. Females also displayed

longer durations of visits to familiar males than to unfamiliar males

(see Table 18), and a greater number of females exhibited more visits

to familiar than to unfamiliar males (one-tall sign test, N=18, 2=5,

p<.05).

Because stimulus animals In familiarity preference tests had

previously been evaluated in aggression tests, the "attractiveness" of

these animals in familiarity preference tests could also be evaluated

on the basis of their tendency to Interact with other animals. These

comparisons are presented in Table 19. Peromyscus Dollonotus females

displayed significantly more visits to high-interaction than to

low-interaction males, and the difference in the number of females that

spent longer durations with high-interaction than low-interaction males

was also significant (one-tail sign test, N=20, x=5, p<.05).























































V)
a,
r-
u
a,

tu 0.


ra U





E 4-


- (E
LL-




Sr- 2









r-
*.- t
E -














rt no
LL 0
S- X



na c>








4- CO


0-
4 *-
S-Q

s-
0- 0

J=


w
L



E
















C. c
10







4-




w
L (





c c








L L
(I






(U


CO N













a- W% Uo
O GO






















0% In 0










in N>
a

























>Nb0
0>- -






































to
z- x


in -











- I
















-- 0
>-





..- -O
0-

000
z -


* N


CM 00
*- 0 f
M N -


- 10 0


0% N




ON G
o0 r-





C\

In
CM 01 0



















'0-
U* .% *

N



o r.








-00












co -


trn 0





0M a
















oco
-0-

SI-








-a
Y--







4-- 0
-4-




0-
000









77












nc ~ a -. co $

N








Sc W% 4 a, n
Ii
4--







E a
S1 4- .

V) :n o0
Eo




S-.r






C4C
0o) 0
4 r -- o 0%

EO o EU
4-- 50 04 NO in %
I 0- C. C4 r- o





s-.
0 .)
4-L/ 4) In
w oL- 0 !

'-4 ( 0 0 a oC'
.) ( --
W r-D .4-- .l..

0 0 c_% in N 0 co


4- E "
toi- ID o









4 Fn C- in %a n
1ro 4-
0) 4 0%I


ro r 0 C- 4 Ln (N y

4- a


cu a O S ^

S- -



b-6


0 0 C
>J >
.4- I.-

S-U



a ; \IiC
01 *I 0-










Discussion

Whereas individuals observed in the seminatural apparatus had

exhibited appreciable levels of aggressive behavior, levels of

aggression displayed by individuals in the aggression apparatus were

very low. This finding was somewhat unexpected. The object of the

procedures followed In the present study had been to condition

individuals to treat the aggression arena as an extension of the home

cage. In previous observations Individuals housed in cages identical

to those used to form the aggression arena had displayed fairly high

levels of aggression to Intruders after one to two weeks of residency

(unpublished observations). In the present study individuals were

tested for aggressivity in the arena on the seventh through ninth days

of residency in the home cage. Although individuals did not have

access to the home cage during aggression tests, they had been allowed

to travel freely between the home cage and aggression arena during

adaptation. In addition, during aggression tests the home cages and

the aggression arena were attached in a manner that allowed a fairly

free flow of air between them. Many Individuals were observed to spend

long periods sniffing and gnawing at the entrances to their home cages.

Individuals therefore appeared to recognize their home cage as opposed

to a strange cage (unfortunately these observations were not

quantified). During aggression testing, however, Individuals did not

behave as residents in the aggression arena, nor did they defend the

entrances to their home cage. Animals In these tests were

simultaneously exposed to olfactory cues from both their home cage and

that of their opponent. These test conditions may have led to










conflicting "fight" and "flight" responses (See Hinde, 1966), and

thereby resulted in low aggression scores.

It Is of interest that Individuals In the seminatural apparatus

displayed high levels of aggression toward one another immediately upon

being allowed access to the central arena, even though none of these

Individuals had previous exposure to this area, and had been in

residence In the connected home areas only three days. The observation

of higher levels of aggression under the seminatural conditions than

under aggression-test conditions may be due In part to the fact that

Individuals in the seminatural apparatus were exposed to opposite-sexed

Individuals during tests while individuals in the aggression apparatus

were not (Barnett, Evans & Stoddart, 1968; Brain, Benton, & Bolton,

1978; deCantazaro, 1981; Flannelly & Lore, 1977; O'Donnell,

Blanchard, & Blanchard, 1981). Exposure to females has been

demonstrated to Increase male-male aggression In P maniculatus balrdl

(Terman, 1982; Dewsbury, Personal communication). Exposure to

opposite-sexed Individuals was, however, not required to elicit

aggression In the previously mentioned tests of resident B. polionotus

in aggression-arena-sized cages; and males in the seminatural

single-housed condition were observed in several tests to Initiate high

levels of attacks and chases prior to exposure to females.

Preferences for high-interaction (and presumably more aggressive)

individuals were not as strong as might have been predicted from the

results of the seminatural experiments in the present study, or from

the results of previous studies (e.g., Blair & Howard, 1944;

Eisenburg, 1962). Although in the majority of comparisons (over 80%)










scores on the measures of preference for high-interaction individuals

were higher than those for low-interaction individuals, most of the

differences displayed between high and low-interaction individuals were

non-significant. This may be a reflection of the low levels of

aggression displayed In these tests. Previous investigators (e.g.

Huck et al., 1981) have hypothesized that the differences in odors

displayed by dominant and subordinate animals are mediated by

differences in the physiological changes Induced in these Individuals

through aggressive encounters. The levels of aggression in the present

tests may not have been high enough to fully induce the physiological

changes necessary for clear-cut discrimination on the part of choice

animals.

Although levels of aggression were low in aggression tests, females

of both species, and E. maniculatus males, displayed significant

preferences for the more "assertive" individual of the opposite sex

under some preference test conditions. Significant preferences were

not displayed for low-interaction individuals of either sex in either

species. Under the assumption that Individuals that are more assertive

would also normally be more aggressive, these findings are consistent

with the hypothesis proposed earlier that Individuals of these species

should prefer aggressive opposite-sexed Individuals, and also with the

nesting behavior exhibited by fP pollonotus In the seminatural

apparatus.

In familiarity preference tests P, maniculatus of both sexes

displayed preference for familiar Individuals of the opposite sex,

while P. polionotus did not display such preference. Although the










lack of preference displayed by E. pollonotus In the familiarity

preference tests Is consistent with observations made in the

semlnatural study, results of the familiarity preference tests are

contrary to predictions made earlier as to the behavior of these two

species.

Sibling Preference Tests

Introduction

Individuals of most rodent species will be exposed to siblings

during development. Such exposure may, of itself or In conjunction

with genetic factors, influence mate selection (Grau, 1982; Halpin &

Hoffman, 1982; Smith, 1966). The general consensus holds that, except

under special circumstances, Individuals should prefer to breed with

non-relatives (Daly & Wilson, 1978; Dewsbury, 1982a; Krebs & Davies,

1981; Wittenberger, 1981). Rasmussen (1970), however, has suggested

that Inbreeding may be fairly extensive in some species of Peromyscus,

particularly P. maniculatus (Rasmussen, 1964); and Howard (1949) has

proposed that inbreeding may account for as much as 10 percent of

breeding in P. maniculatus. Smith (1966) has suggested that "a

considerable amount of Inbreeding" (p. 50) also occurs in En

pollonotus.

Not all Investigators agree with these proposals however.

Selander (1970) has questioned the genetic basis for Rasmussen's (1964)

conclusions regarding E. maniculatus, and other Investigators

(Dewsbury, 1982a; Hill, 1974) have demonstrated suppressed

reproduction for sibling matings in this species. Foltz (1981b) has

also questioned Smith's (1966) proposal of high levels of inbreeding In










P. pollonotus. The present study was designed to evaluate preference

for siblings in P. pollonotus mand. P maniculatus.

Subjects

Both P. pollonotus and ,. maniculatus served as subjects for

sibling preference tests. Subjects were selected from 12 litters of

each species that contained at least two animals of each sex. Two

animals of each sex were selected from these litters, under criteria in

the general methods section, and maintained together throughout the

experimental procedure. Litters selected for groups were unrelated by

more than one common grandparent. Two litters of each species

comprised an experimental group.

Procedure

Individuals were ear-punched for identification, and .

maniculatus litters were moved to the P. pollonotus colony room. On

the following day animals were adapted to the preference apparatus,

without other Individuals present, as both stimulus animals and choice

animals.

Preference tests were of two types, same-sex tests and opposite-

sex tests. In same-sex tests choice animals had a choice between a

same-sexed sibling stimulus animal and a same-sexed nonslbling. In

opposite-sex tests animals had a choice between two opposite-sexed

individuals, one a sibling and one a nonslbling. Each animal in a

group served twice as a stimulus animal and once as a choice animal for

each type of test. In an opposite-sex test, for example, males 2 and 4

would serve as stimulus animals for choice females 2 (one of the 2 male

siblings) and 4 (a 4 male sibling). They would each also serve as










choice animals with stimulus females 1 (a 2 male sibling) and 3 (a 4

male sibling).

Preference tests were conducted on the two days following

adaptation. All tests of one type (i.e. opposite-sex tests) and half

of the tests of the other type were conducted on the same day. Testing

was completed on the second day. The order of test type across days

was counterbalanced. The number and duration of visits to each chamber

were recorded on each test and for the adaptation period. Vaginal

smears were obtained for each female before the beginning of the dark

cycle on each test day.

Results

Peromyscus polionotus females demonstrated a preference for

siblings over nonsiblings (see Table 20). Sibling males were visited

significantly more frequently than nonsibling males, and a

significantly larger number of females spent longer durations with

sibling rather than nonsibling males (sign test, N=24, x=6, 2-tall

p<.05). They also spen+ significantly longer durations with sibling

rather than nonsibling females. None of the comparisons for siblings

versus nonsiblings were significant for P. pollonotus males or for EP

maniculatus of either sex (see Tables 20 and 21). It is, however, of

Interest that scores for P. pollonotus males on tests with opposite-

sexed animals mirror those of P. polIonotus females (higher scores for

siblings), while for all but one measure (average duration of visits

for females) E. maniculatus display higher scores for opposite-sexed

nonsibllngs.










84











N ~ N

-0 Nc N


-N N-O


0 t
Z T C coc
aa,
Ei Z r e-

0
0 CM i
E Q O co in c


tA aN %0i

0) CQi, co e


o +

C) 0C



cn Ln c r


0x C -0 (NM




w) w In
-E 2
co O- C-ON
rOW C Ce OIOQ







(1 1C *- *4*-
00 N a

r-E
O c-4or- -n





Ia 0 O pp C40
- -1N
* 0 M
rQ s C(4 *


CA% 0 o %0
r-S +N WI



4- 4-
NC-


do 00 ;c
(UJ aa %-c- n
(j 00 co N.
x a% C> mmo N OM
ao Wc x-
W) li 0 -i a

U C -cl MO-N N V





MCO C
Sc 0T M -&-l







0

+- 2N a 0,


0- o- 10 0
0 0 C0
C4 C 00( 0 0)

u c = 4- I x
0*- 0*- L4-
0 O 00







2: 2<
.4-0 --














































X







a)


- L



LL.




5c-
oo


n I

.- -

n3



-4-
ro
*- I4



EA
ro c










o -o


v,


c




0 cU






z )





















(D
4-






C 0
in




























c c
0 (0



























z C
M
Z "


r- 01 p-
SCo -
KC 0



a) ( F4


N
in C4 -


C CO
(N

S0\0



N c-
r-O -
.O. V%
N -
- o -


%0 Lco
- %0 co
-*










\o*
cM
00 0 0







co o
;0U-


F- (N -


N

+- 4-

- CO 0
ao

10 4 -



o> co




0 0 Q)
















CO -



-4--






4-- 0
-0 3






0-

000
2 1-


fHao







N -





--10 %

(N r- c
MCIO a0
(N



co !n
O W-0






C in



N



N1
-







-n N
CM N-










r- (n





0 mF


N M IA





00
0> -~
con







AA
ra,
-om
U)~-


















to
0 (0
NC




ne.















-- 0(D
z 2:



-4--
0-
S- m
>-





T

+-


0 0
2 -












Table 22

Comparison of Male Preference for
Sibling and Nonslbling Females in Diestrus


Sibling Nonsibling

Measure Mean (SE) Mean (SE) t


P. polionotus

No. of visits
Total duration of visits
Mean duration of visits


L maniculatus

No. of visits
Total duration of visits
Mean duration of visits


90.83
777.06
28.66


18.21
1048.67
87.96


24.40
173.36
13.16


4.45
323.90
35.79


95.33
904.81
35.11


14.64
1448.26
201.42


21.10
259.62
15.51


3.22
367.33
84.01


1.36
.64
1.12


All durations are in seconds.
-test P. polionotus dL=11
p>.05 for all comparisons


P. maniculatus df=14


2-tall






















% % co CM U"% 3
Go 0 0 r- 'T




u, U) Nq,)-N'o
W n 03 NNC
in 1n M T (>

4-
ID Z %O'0 %0%0%0



0 ca
o) a (M 94 M ~c -
SCD r- % -0w




o C-

4- Z 0 w C 0 r-r-N






co
40-
C- 0C
t( Qe co arcoor-

E E -oOIN


VI0 N I .. .



4-) 1
f C1O C 00 CO


*in V C)
C2 C1 C14

(o re a D z 'o 'D O 'Doio
o E o)

Cd 1 0 0 I WI) Nw -



a) r Q1 0 a a I 5oa%
0) 0 ogoo o a
o co- i
co W CUh ON 4 ao


*Or0 M Ccla

m w 0 co C n
(Ai - -
4-m
% N N CO% C



0 3o ou

a) X CA-KnN CN -
U- r 10



OIn
Q'0) a









me >
S* -U 00 a

4- OOo o a m

CC C C0


Q)+-- 4- o






--LL--
0 0 0- a
.c >
S0 0COC -0







0 0Z 0 01 a0
5:- Z +- C -:
--ut rn n -







II I-fl 4 4 0 0-(










88






*
in C r- 0% r-
St *N s tcN



LU I- oT a' N-
I Ao0 %0 i
WN
2






4- a -,ce
S Z vo





C
I a M






C NC



c&n
co omu*noomo
(A4 4 -






N a LU Nme
cn E rU !
2 CM -




0 4t- Z -ocoo rc n



0 =II I 23 ooor a





U) C %0
a ro






0rC.
-0 4-
a 0 0 CCanm ar-


C O i N hN-IOr-






S. .

/) a: CM 4- -
& C-



U) 4-)


0O m 1 o CAi
me




SC --W
0> 0




(a C C C i V
a a






0 0 C 01 0

,.5 o4 0 a r_
+-- 0 *
cL i CI





0 I C 0 0






01 o o 2
S i -
-0 -




S0) 0 0 -

x -- m z x
-0>>---


3 0 0 0
SU100cc




--C) O B D"2



S zzt-c-. <1









89







%0!? 0% C4 ,



co 'n N Nin I'


W o






S ra. r- goo .n No-W
( to \or







4--








rl
e z on nnm-U


So o n
mi 0 1 D. .
O 0 >0r

4-










-n W- c .
UI-




0 i- co




4"-- .0 -- 0





r- *rrG a
CULL ) Z ur-p--i










P fo %0 -NW M O- a
LL.






























A -
0V) N2" 0













c ---r
-C)











S-t- -. .

c-r-1 0 0- cncm 0












00--ca~
+ 43) rzN iN 9

S s% 04
En '0 LN%% a0n



Q----










-C-
on



W C
' z- 0 4- o SOrI A



a) = 0 oo or





O l c mC +OO o
U,




a) O I On=
o o
1-c -.Z L








0 N QO> N> -0
V 00









0- 0 0
gj C iri~mmmin >

0 N S MOO- N- 0
0n '0 oO














in c l *o 0
a.-- O cN



Sin c C > -








0 0 0 m -
In >











cl I c









0 c 4- 00 4-





_0 0 0 C 0 )
-n-x



0)00 03
C 4- 4- 0 0

--n~--4-4-







4- 4z l--- 0



In 00CC
3c 4 4- 0-
0 00000
z zz-,-ri










As with the aggression preference tests comparisons were made of

male preference for siblings and nonslblings In diestrus and of male

preference for diestrous versus non-dlestrous siblings and nonslblings.

None of these comparisons were significant for either EP pollonotus or

EP maniculatus males (see Tables 22 and 23). Comparisons of the

preferences of females in different stages of estrus did, however,

yield some significant differences. Although P. pollonotus females

exhibited no significant differences in preferences based on stage of

estrus, P. maniculatus females did display significantly greater

preference for nonsibling males, by the measures of total and average

durations of visits, when in a non-diestrous condition over a diestrous

condition (see Tables 24 and 25).

The possibility of litter effects on preference scores was also

evaluated by conducting a one-way analysis of variance on the

"difference scores" between preference scores for siblings and

nonsiblings. Significant litter effects were found for the average

duration of visits by E pollonotus males to females (F(11,12)=3.77,

-<.05). and for the total duration of visits by EP pollonotus females

to males (F(11,12)=3.08, p<.05).

Discussion

While Peromyscus pollonotus males generally displayed higher

scores on preference measures for siblings than for nonslbllngs, these

comparisons were not significant. PE polionotus females, however, did

display significant preferences for siblings over nonsiblings. The

results of this study, therefore, may offer some support for proposals

of high levels of Inbreeding in P. polionotus (Smith, 1966). The










observation that scores for preference by EP maniculatus males and

females were generally In the opposite direction from those for P.

polionotus Is of Interest. This difference may indicate a greater

preference for siblings by F. polionotus than by P. maniculatus.

It is also of interest that non-dlestrous P. maniculatus females

displayed a greater preference than diestrous females for nonsibling

males, since females in a non-dlestrous condition would be more likely

to be receptive. These results are consistent with previous studies

demonstrating suppression of reproduction in sibling matings of P.

maniculatus (Dewsbury, 1982a; Hill, 1974), and the implicit conclusion

from these studies that inbreeding should be avoided by members of this

species.














SECTION IV
GENERAL DISCUSSION

In the general discussion the observations of the present study

are examined in light of previous research, and interpretations are

suggested for these observations that are consistent with the ecology

and mating systems of f. maniculatus and E. polionotus. The general

discussion section is divided into six subsections. The first of these

subsections examines aggressive ability as a factor in preference.

This subsection begins with a fairly extensive overview of the ecology

of P. maniculatus and P. polionotus, and also presents evidence for

the role of aggression in the ecology of these two species. The

ecological information presented in this subsection serves as a

background for discussions which follow in all subsequent subsections.

The discussion of the ecology of these species is followed by a

discussion of factors that may provide an adaptive basis for selection

of aggressive mates in these species.

The second subsection deals with familiarity as a factor in

preference and with the effect of prior breeding experience on

preference for familiar individuals, and includes a discussion of the

opportunities that may be available for P. maniculatus and P.

polionotus to utilize familiarity as a basis for mate selection. This

subsection is followed by a subsection on the related topic of kinship

as a factor in preference. The subsection on kinship discusses










evidence for and against inbreeding in maniculatus and P.

pollonotus, and the ecological and social factors that may affect

preference for siblings as mates in these species. This subsection is

followed by a subsection on the evolution of monogamy in P.

pollonotus, and the summary for this study.

Aggressive Ability as a Factor in Preference

Many of the observations In the present study were consistent with

the general hypothesis that aggressive ability may be Important in the

social behavior and mate selection of monogamous and polygamous

species. They were also consistent with the specific predictions that

aggression should be an important component of the social behavior of

P. pollonotus, and that P. pollonotus and P. maniculatus of both

sexes should prefer mates with high aggressive ability. In the

seminatural experiments aggression was routinely displayed by both

male and female P. pollonotus, and both males and females of this

species nested more frequently with the more aggressive of the two

opposite-sexed individuals. Female P. pollonotus also displayed

preference for the more assertive of two males in familiarity

preference tests; and preference for more assertive individuals was

displayed by P. maniculatus males and high-interaction P. manlculatus

females in aggression preference tests.

The preferences exhibited by these species may be mediated through

advantages in reproduction gained by individuals that choose mates with

good aggressive ability over those that choose mates with poor

aggressive ability. Some of the possible advantages accrued by

Individuals that choose mates with high aggressive ability have been




Full Text

PAGE 1

AGGRESSION AND FAMILIARITY AS FACTORS IN ~ATE SELECTION IN Peromyscus pol jonotus AND Peromyscus manjcu!atus BY DANIEL GEORGE WEBSTER A DISSERTATION PRESENTED TO THE GRADUATE (X)UNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1983

PAGE 2

To my wife Carole and my daughter Daniel le and to my parents

PAGE 3

L AO
PAGE 4

TABLE OF CX)NTENTS PAGE AO
PAGE 5

Slbl Ing Preference Tests 81 I ntroductl on 81 Subjects 82 Procedure 82 Results 83 Discussion 90 IV GENERAL DI SQJSS I ON 92 Aggressive Abll lty as a Factor In Preference 93 Ecology, Mating System, and Aggressive Abll tty 94 Peromyscus manlculatus 95 Peromyscus polionotus 101 Aggress I on and Mate Se I ect I on 106 lntraspeclflc aggression 106 lnterspeclflc aggression 108 Ear I y breed Ing . . . . . . . . 109 Bruce ef feet 109 Her I tab I e aggress Ive ab 11 I ty ....... ........... 111 Familiarity as a Factor In 113 Pr I or HI story 114 Eco I ogy and Soc I a I Sy stem 115 Peromyscus manlculatus 115 Peromyscus pol lonotus 117 KI nsh Ip as a Factor in Preference 119 Inbreeding In Peromyscus manlculatus 120 Evidence for and against Inbreeding 120 Ecological and social factors 121 Inbreeding In Peromyscus pol lonotus 125 Ev I dence for and against Inbreed Ing 125 Ecological and social factors 126 Evolution of Monogamy In Peromyscus Polionotus 129 Summary ............................... 133 REFERENCES . . . . . . . . . . . . . . 137 BIOGRAPH I CAL SKETO-l 162 V

PAGE 6

Abstract of Dissertation Presented to the Graduate Councl I of the University of Florida in Partial Fulfi I lment of the Requirements for the Degree of Doctor of Philosophy Chairman: AGGRESSION AND FAMILIARITY AS FACTORS IN MATE SELECTION IN Peromyscus pol jonotus AND Peromyscus manjculatus By Daniel George Webster Apri I 1983 Major Department: Donald A. Dewsbury Psychology Aggressive ability and familiarity were examined as factors in the social preference and mate selection of males and females of the monogamous species .E.... pol ionotus, and the polygamous species .P.... manjculatus. The aggressive behaviors and nesting behavior of .E.... pol jonotus were observed in a semi natural apparatus; factors assessed were 1) fami I iarity based on cohabitation, and 2) aggressive ability as determined through aggressive interactions. Groups observed were composed of either two pairs of familiar opposite-sexed individuals, or two unfamll iar animals of each sex. Preferences of both species were assessed in an automated preference apparatus. In addition to the two factors assessed In the seminatural apparatus, the effects of familiarity based on relatedness were assessed in the preference apparatus. Measures recorded were the number and duration of visits vi

PAGE 7

L to stimulus animals. In the semi natural setting .E... pol jonotys of both sexes displayed aggression, and nested more frequently with the more aggressive of two opposite-sexed individuals. Males of this species also exhibited a behavior, aggressive digging, that may signal their aggressive status. Peromyscus pol jonotus and .E... manjculatus of both sexes exhibited evidence of preference for more assertive opposite-sexed individuals (high rather than low tendency to interact) in the preference apparatus. Peromyscus manjculatus of both sexes also displayed preference for individuals of the opposite sex that they had previously been housed with, but such familiarity did not affect preference in .E... pol jonotus. The lack of a significant effect of famil iarlty on preference in .e... pol jonotus was consistent with the nesting behavior of this species in the seminatural apparatus. Differences in the responses of .e... manjculatus and P.... pol jonotus to faml I iar individuals may be based on differences in the opportunities Individuals of these species have to use this factor In mate selection. Peromyscus pol ionotus females demonstrated significant preference for sibl lngs over nonslbl ings, and males tended to display higher sibling than nonsibl ing scores. Inbreeding in P.... pol jonotus may permit individuals of this species to found populations In isolated patches of favorable habitat. Lack of significant preference by .E.. maniculatus for slbl ings or nonsibl lngs was Interpreted as due to competing preference responses In this species. vii

PAGE 8

SECTION I INTRODUCTION The success of an organism In leaving a numerous posterity Is not measured only by the number of its surviving offspring, but also by the qua I lty or prob ab I e success of these offspring. It is therefore a matter of Importance which particular Individual of those aval I able is to be their other parent. (FI sher, 1 958, p. 143) Few factors are as important to an individual's reproductive success as is the selection of a mate. Mate selection Involves more than simply the identification of potential partners as to species and sex. In order for an individual to maximize Its future representation In the gene poo I it must a I so se I ect the "best" poss I b I e mates on the basis of a variety of other considerations. There has been much theoretical speculation on the proximate and ultimate bases of mate selection and on the relative Importance of mate selection to dlffe~ent mating systems. In the last decade a considerable effort has been made to collect empirical data on mate selection, but large gaps stl I I remain in the existing data which must be fi I led before many Important theoretical problems can be resolved. Particularly lacking are data on male choice and data on mate selection In mammal Ian species, especially those considered to be monogamous. The lack of data on male choice probably stems In large part from a traditional emphasis on female choice and male-male competition (Bateman, 1948; Daly & Wilson, 1978; Trlvers, 1972; 1

PAGE 9

2 WI 11 lams, G. C., 1966) and the belief that male choice was either nonexistent or neg I igible In the face of this competition. More recently, however, It has been suggested that mate selection should be of sane consequence to males as wel I as females (e.g., Dewsbury, 1982c). The lack of data on monogamous mammal Ian species may be due In part to two factors that make It sanewhat difficult to observe these species: 1) monogamy appears to be uncommon in mammals (Alexander, 1974; Crook, 1977; Kleiman, 1977; Orians, 1969) and 2) most manmals, especially the smaller species, are largely nocturnal (Vaughan, 1978). Study of the proximate factors Involved in mate selection is extremely important to the resolution of issues about the evolution and relative importance of mate selection in various marrrnal ian taxa. Factors that have been proposed to be of major importance to mate selection are of two general types: those related to the genotype of a potential mate, such as genetic quality (Trivers, 1972, 1976; Zahavi, 1975), and relatedness (Maynard Smith, 1956); and those related to resources, such as the ab 11 i ty to accrue resources (Tri vers, 1976) and parental investment (Bateman, 1948; Trlvers, 1972). The relevance of any particular factors as criteria In mate selection wil I vary among species, between sexes, and across mating systems, as a function of differences In a group of interrelated variables Including ecological factors (Borgia, 1979; Emlen & Orlng, 1977; Halliday, 1978). Differences in the degree to which Individuals of various species utilize particular factors as criteria in mate selection would be expected to reflect differences In the adaptiveness of those criteria to mate selection in those species. Comparative studies of mate

PAGE 10

3 selection or social preference In different species, therefore, can provide an empirical basis for evaluation of hypotheses on the importance of various factors to mate selection under different social or mating systems. Such comparisons would be most effective when the species compared were closely related (King, 1970) so that the species do not differ in so many respects as to obscure the relationships of interest. Two factors of the sort that might be expected to be of broad importance as criteria for mate selection across most species, but may be expected to vary in importance among species, are the aggressive abll ity of a potential mate, and that animal's degree of familiarity with the Individual expressing choice. An individual of high aggressive ability could be defined as one that is highly competent in the performance of aggressive behavior (I.e., displays, threats, and fights). Individuals of high aggressive ability would be expected to perform wel I in competition for contested resources and defense of mates and/or offspring. Familiarity can be of two types, these are 1) familiarity gained through exposure to other unrelated individuals, and 2) fami I iarity with kin. In the first sense, fami I iarity may provide a basis for evaluation of former mates or a means of discriminating between two potential mates. In the second sense, famil iarlty may provide a basis for avoidance of inbreeding, or as a yardstick for comparison of potential mates (Bateson, 1978, 1980). This study was designed to provide data on the importance of aggression and famll iarity as factors affecting mate preference in males and females of two closely related species of muroid rodents with

PAGE 11

4 different mating systems: the monogamous species Peromyscus pol jonotus and the polygamous species Peromyscus manjculatus. In I ight of the relative lack of data on mate selection in monogamous species the major focus of this study is on .E.i. pol jonotus. The discussions that fol low provide a brief review of relevant theoretical factors in mate selection, and a demonstration of the Importance of aggression and fami I iarity as factors in mate selection, with an emphasis on mammalian species. Aggression as a Factor in ~-late Se I ect ion Darwin (1859) recognized that sane males could gain a reproductive advantage over other males by defeating them in fights tor females. It has been suggested (Bateman, 1948) that t~e evolution of male-male competition had its basis in differences In male-female strategies of investment in gametes. Males are generally considered to invest I ittle energy in the production of gametes, whereas females invest a great deal (Bateman, 1948; Orians, 1969; Stacey, 1982; Trivers, 1972). Because of their larger investment females are valuable to males, and the probability that females wi I I obtain mates is high, but their reproductive success wil I be I lmited by the number of gametes they can produce. Males, however, because they invest I ittle energy in the production of individual gametes, can afford to produce large numbers of gametes--with which they could potentially fertilize large numbers of females. A male's reproductive success, therefore, may be greatly influenced by the number of females he mates with--and males may be expected to compete to ferti I ize females (see however, Dewsbury, 1982c;

PAGE 12

5 Nakatsuru & Kramer, 1982). This argument was extended by Trivers (1972), who restated It in a more general form based on the overall relative level of parental investment of the two sexes, which he hypothesized to determine the intensity of male-male competition in species as wel I as the form of the mating system (see however, Kleiman & Malcolm, 1981, p. 371; Wickler & Seibt, 1981). The level of success achieved by a male in competitive mating may often depend upon his abll lty to dominate other males. This notion has been examined in a wealth of studies, recently reviewed by Dewsbury (1982b), on the relationship between "dominance" and various aspects of reproduction. A male's abll ity to conquer other males, however, also provides females witn a basis by which to judge him against other males--a basis tor "female choice" (Darwin, 1874). Borgia (1979) has suggested that a female's best indication of the relative overall genetic quality of a male is provided through his aggressive Interactions with other males. Females choosing aggressive males, or al lowing such males to mate with them, may in effect be selecting "good genes" for their offspring (Maynard Smith, 1956; Trivers, 1972). Selection for good genes has also been suggested as a basis for the evolution of extra vagant sexually dimorphic characteristics (Fisher, 1930), as a basis for lek behavior (Borgia, 1979), and as a basis for female choice in Drosophila (Partridge, 1980). The major obstacle to the use of heritable factors as a basis for choice is the problem of "using up" the genetic variance for a trait (Krebs & Davies, 1981; Maynard Smith, 1978). Several factors, however, have been suggested to act to maintain genetic variance; these Include 1) advantages for

PAGE 13

L 6 heterozygotes (Borgia, 1979), 2) variation in the optimal genotype in space and time (Krebs & Davies, 1981), 3) factors such as chronic parasitism, that may result in cyclic changes in the optimal genotype (Hamilton & Zuk, 1982), and 4) rate of mutation in polygenic characters (Lande, 1976). The northern elephant seal CMjrounga angustjrostrjs) provides an example of the importance of male aggressive abi I tty in female choice in a natural setting. During the breeding season males of this species establish dominance hierachies which are maintained through threat and combat. Dominant males guard groups of females from other males, and account for the majority of first copulations CLeBeouf, 1974; LeBoeuf & Peterson, 1969). Females help insure that they wil I b e inse m inated by an aggressive dominant male by vocalizing loudly if a subordinate male attempts to mount. The dominant male, alerted by the female, drives off the subordinate male and copulates with the female (Cox & LeBoeuf, 1977). The authors note that females of many polygynous species might be expected to incite male-male competition in this manner. Cox (1981) has observed that female elephant seals are less I ikely to vocalize If the male mounting them has just displayed dominance over another male and suggested that females may thus select for males that frequently display their aggressive abi I ity. Cox hypothesized that in general "in species where social status of males Is correlated with their genetic fitness, female choice is I ikely to be based on social signals which are used in competition between males" (p. 197). Similar hypotheses have been proposed by Borgia (1979) and Alexander (1975). Cox (1981) has provided examples of several species in which females appear to use male's aggressive signals toward each other as a basis for choice. The

PAGE 14

7 list consists of a fairly diverse array of species including territorial birds (Armstrong, 1973; Thorpe, 1961), tree frogs 0/hitney & Krebs, 1975a, 1975b), sticklebacks CTinbergen, 1951), and a lek-forming bird, the ruff .E.b.lJ.Q{!lachus pugnax (Hogan-\'larburg, 1966). M ale aggressive abi I lty need not be heritable or manifest at the time of mating to be an important factor in female choice. Male differences in aggressive abl I ity, for example, wli I be related to differences In their ability to acquire and hold territories
PAGE 15

8 odors. Ovariectomized sexually naive females displayed no preference in hormonally induced estrus. Ovariectomized sexually experienced females preferred dominant males when not injected with hormones, but subordinate males when in hormonally induced estrus. As discussed earlier a female may often invest relatively more than a male In offspring, and a female's reproductive success may often be more I imited than a male's. Because of these factors females are generally considered to be more choosey than males when selecting mates (Bateman, 1948; Burley, 1977, 1981; Daly & Wilson, 1978; Trivers, 1972; Wi I Iiams, G. C., 1966) and the majority of studies of social or mate preference have been studies of female choice. Male reproductive success, however, depends on not only the number of mates males acquire but the quality of these mates as wel I <\\lade, 1979). Ral Is (1976) has, for example, suggested that larger females may often be better mothers. Factors such as this might be considered trivial if males were capable of inseminating an uni imited number of females. However, although males appear to produce an enormous number of sperm and therefore to be capable of inseminating an enormous number of females, these sperm are emitted as ejaculates--of which a male may produce only I imlted numbers (Oewsbury, 1982c; Nakatsuru & Kramer, 1982). Mate selection may, therefore, often be of some consequence to males as wel I as females (Dewsbury, 1982c). The aggressive ability of females may be an important criterion for male choice. Females with high aggressive ability may be more capable than females with low abi I ity in such behaviors as defense of young or nest sites, or in competition for food items. Males of some species

PAGE 16

9 have also demonstrated an abi I lty to discriminate the aggressive status of other Individuals, and therefore the potential to use this factor in mate selection. Male rats, for example, spend more time investigating odor from a dominant male than from a subordinate (Krames, Carr, & Bergman, 1969). Male mice also discriminate between the odors of dominant and subordinate males (Carr, Martorano, & Krames, 1970) and investigate areas marked by dominant males less than those marked by subordinate males (Jones & Nowel I, 1973). Both male and female saddle-backed tamarlns Investigate dominant male scent marks more than those of subordinate males (Epple, 1973, 1974). Although the majority of preference studies to date have been conducted with polygamous species, there is no reason to believe that members of monogamous species should be any less adept at discriminations based on differences in aggressive status, or that the ability to make such discriminations should be any less useful to members of monogamous species. Aggression serves many of the same functions In monogamous species as in polygamous species. Although male-male competition and aggression near the time of copulation may be less important in monogamous than In many non-monogamous species, aggression serves many functions at other times in an organism's I lfetlme, and success In these other aggressive encounters wil I be just as important to monogamous as to polygamous males. For example, defense of resources critical to raising young, and in many cases to initially attracting a mate, is hypothesized by some authors to be universally displayed by males of monogamous species. Kleiman (1977) states that "The male's territorial defense, which prevents the over

PAGE 17

10 utl I lzatlon of necessary resources, is practiced by males of al I monogamous species" (p. 54). Kielman (1977) has also indicated that females of monogamous mammal Ian species may commonly be as involved as males in territorial defense and contrasts this behavior with a lack of territorial defense by non-monogamous females. This hypothesis is similar to one previously proposed by Wilson (1975) as one of the biasing ecological conditions for monogamy that two adults are required to defend valuable resources contained in the territory. If monogamous females help to acquire and defend resources then monogamous males may dowel I to choose aggressive females as mates. An additional consideration, related to the possible function of aggression as a factor in mate selection in monogamous species, Is the "early breeding" hypothesis proposed by Darwin {1874). According to this theory the most healthy, more dominant members of a species wil I come into breeding condition earlier in the season, and establish territories earlier, than the less vigorous subordinate individuals. The more dominant individuals of each sex should then choose each other as the "better" mates in preference to subordinate individuals. Two species whose behavior may support the occurrence of this form of selection are the artlc skua (Stercorarjus parasjtjcus> and the mourning dove
PAGE 18

11 related to male abll tty to hold large territories (Davis & 0 1 Donald, 1976). Dominant male mourning doves prefer dominant females In experiments with penned populations (Goforth & Baskett, 1971). Dominant pairs breed earl !er than subordinate pairs, and more offspring of dominant pairs survive. Based on theoretical considerations, and on the results of research conducted to date, predictions can be made as to the relative importance of aggression as a factor In mate selection In species with polygamous and monogamous mating systems. Males that are above average In their aggressive abl I ities should generally be preferred as mates by females of monogamous and polygamous species. Females of monogamous species, because they may form long-term pair bonds and consequences of their choice may therefore be more long-term, might be expected to display stronger preference than polygamous females. Males of monogamous species might be expected to display preference for females with higher aggressive abil lty because, among other considerations, such females may be In breeding condition earlier and might be expected to better share responslbil ity for territorial defense. Polygamous males might also prefer females with higher aggressive abi I ity because such females may be better able to defend young or resources necessary for raising young, but preference should not be as critical for these males as for monogamous males. Famil iarlty as a Factor In Mate Selection Famll iarlty could be an important factor In mate selection In several ways. It would be expected, for example, that early famll rarity with conspeclflcs should aid Individuals In discriminating

PAGE 19

12 between members of their own and other species. Fami I iarity could additionally be an important factor in recognition of kin, and therefore a factor of importance in kin-selection and in avoidance of inbreeding. It may also be of importance to animals of many species to be capable of discriminating between unrelated strange and familiar Individuals. Two aspects of familiarity, recognition of kin and of familiar others, wi I I be discussed further. Kin Fami I iarity Bateson (1978, 1980) has hypothesized that early experience with kin Imprints individuals to aspects of both kin and species, and that such kin fami I iarity is Important to selection of mates of the appropriate species and to avoidance of inbreeding at sexual maturity. Avoidance of inbreeding Is an important consideration in mate selection because inbreeding often leads to inbreeding depression--a reduction in the vlabi I ity of inbred offspring and/or of their ab! I ity to reproduce. Inbreeding depression has been documented in a variety of species from ungulates
PAGE 20

13 may be mediated by adult aggression in many species (e.g., langurs: Sugiyama, 1965; elephant-shrews: Rathbun, 1979). However, female (and male?) choice has also been suggested as a factor (Hoogland, 1982; Wittenberger, 1981) since individuals should be selected to emigrate from natal groups if 1) relatives refuse to mate with them and 2) alternative mates are not readily aval I able. In at least some rodent species reproductive maturity may be inhibited by pheromones produced by adults (Bedlz & Whitsett, 1979; Drlckamer, 1979; Lawton & Whitsett, 1979; Lombardi & Whitsett, 1980). For young of such species emigration from the natal group may provide the major opportunity for reproduction. Although it would appear that avoidance of inbreeding should generally be the rule, certain circumstances may favor Inbreeding. if Inbreeding were not detrimental, Individuals could increase their inclusive fitness through mating with relatives (Bengtsson, 1978; Maynard Smith, 1978). Female control of the sex of offspring In the wasp Euodynerus foramjnatus may be used to counterbalance the detrimental effects of inbreeding and al low individuals of this species to take advantage of the increase in relatedness resulting from inbreeding (Cowan, 1979). Bengtsson (1978) hypothesized that It would be adaptive for individuals to Inbreed if the costs of inbreeding were lower than the costs that would be Incurred in dispersal or in competition for mates in the natal group. Costs incurred through dispersal would include such factors as increased exposure to predators and to unfavorable environmental conditions. Inbreeding may also at times be suited to specialized environmental situations; as noted by

PAGE 21

14 Mayer (1970) "An outbreeder may also be so wet I buffered that it stagnates evolutionarily. At the other end is the extreme inbreeder which has found a lucky genotypic combination that permits it to flourish in a specialized environmental situation (p. 245). Shields (1982) compared the advantages and disadvantages of outbreeding, inbreeding, and asexual reproduction and concluded that inbreeding is often more advantageous than commonly assumed and should be "expected to be co1T111on in organisms produced by stable I ineage environment associations" (p. 274). Although inbreeding may be adaptive under particular circumstances individuals of most species should, given a choice, prefer to breed with nonsibl ings rather than siblings. Some support is lent to this statement by the observation that the initiation of breeding in sibling pairs is often delayed in comparison to the initiation of breeding in nonsibl ing pairs (Batz Ii, Getz, & Hurley, 1977; Dewsbury, 1982a; HI I I, 1974; ~~Guire & Getz, 1981 ). The contribution of preference per se to these findings is, however, difficult to assess. Animals in these studies were not al lowed a choice of mates and delayed reproduction, or lack of reproduction, may result fran several factors
PAGE 22

15 defined in terms of differences in the amount and type of contact an individual has had with others. Familiarity in this sense is an important factor in many aspects of an animal's behavior, including mate choice. Individuals should improve their reproductive success by retaining mates that they have previously bred successfully with and choosing unfamiliar others over mates with which breeding has previously failed. Coulson (1966), for example, found kittiwakes (~ trjdacty!a) were much more I ikely to change mates if breeding had been unsuccessful; and red-bi I led gul Is (!...al:..JJ.s novaehol fandjae scopuf inus) exhibit simi tar behavior (Ml I ls, 1973). Although some authors (e.g., Hal I iday, 1978) have indicated that mate choice based on previous reproductive performance should only be of importance to species which pair bond for more than one season, a I I that is actually required is an ability to recognize previous mates. This abl I ity has been demonstrated in several species including rats (Carr, Demesquita-Wander, Sachs, & Maconi, 1979; Carr, Hirsch, & Balazs, 1980; Krames, Costanzo, & Carr, 1967), lemmings (Huck & Banks, 1979) and prairie voles 0 /ard, Baumgardner, & Dewsbury, 1981). The abi I ity to recognize previous mates may also enhance reproduction through al lowing earlier breeding. This function of fami I iarity has genera I I y been stressed for monogamous species (e.g., Da I y & Wilson, 1978; l 1 /ilson, 1975). The advantages of fami I larity to mate selection, based on reproductive performance or early breeding, are related to an individuals previous breeding experience. Fam ii iarity may, however, also bias selection of mates by sexually inexperienced individuals.

PAGE 23

16 Females may, for example, require a male to exhibit some evidence of "commitment" to forming a pair-bond prior to copulation. The male may fl I I this requirement by investing a large amount of his time in the relationship, and thus preclude his finding another female ( M aynard Smith, 1977), and/or by demonstrating his ab! I ity to provide resources (e.g., Nisbet, 1973). Evidence of commitment is I ikely to be most important to members of monogamous species, especially those In which Individuals form prolonged or I ifelong bonds, because many Individuals of these species may only choose a mate once in their I ifetlme. Individuals of species that form prolonged pair bonds might also be expected to be more "prepared" (Seligman, 1970) to recognize differences In familiarity, than would be individuals of species that do not pair bond, If famil larity were Important to the maintenance of pair bonds. Many authors have indicated that males of polygamous species should mate with as many different Individuals as possible (Adler, 1978; Bateman, 1948; rJawk Ins, 1 976; ~/ i I I i ams, G. C., 1966; Zucker & Wade, 1968). Although as noted previously males may have a I lmlted capacity to mate and should therefore be somewhat selective when al lowed a choice of partners (Dewsbury, 1982c; Nakatsuru & Kramer, 1982), it may sti I I often be to a males advantage to obtain additional matings If the opportunity ls presented. Famil iarlty may therefore be of importance (at least to polygamous males) in identification of females a male has already mated with. However, because mate infidel lty could have serious consequences for monogamously mated individuals (Grafen & Slbly, 1978; Trivers, 1972),

PAGE 24

17 it is I ikely that individuals of monogamous species have been selected to detect potential philanderers, and to select against such individuals as mates (e.g., Erickson & Zenone, 1976). It may be expected therefore that polygamous males would be more I ikely than monogamous males to prefer novel over fami I iar partners. This prediction is consistent with previous suggestions that males of monogamous species should be less I ikely than males of polygamous species to exhibit a "Coolidge effect" (Thomas & Birney, 1979; 1-'/ilson, Kuehn, & Beach, 1963; but also see Dewsbury, 1981a,b). As a general set of predictions it might be expected that individuals of monogamous species would display greater preference for fami I iar individuals than would individuals of polygamous species. Because of differences in the consequences of choice it might also be expected that femeles would display stronger preference than males (e.g., Burley, 1981). Monogamous females would be expected to display the strongest preference for familiar individuals. Monogamous males should be expected to display some preference for fami I iar individuals, as might also polygamous females (unless greater benefits result from producing multiply sired I itters). Polygamous males, however, due to a greater possibility of increasing their reproductive success through mating with more than one female, may be expected to display some preference for novel individuals of the opposite sex.

PAGE 25

SECTION I I GENERAL EXPERIMENTAL CONSIDERATIONS AND METHODOLOGY The discussions In this section provide a brief rationale for the choice of the particular species and experimental procedures that were fol lowed In this study. This section provides general methodological Information common to al I experiments In this study, and a description of the apparatus used In these experiments. Selection of Species One of the methods that may be particularly suited to exposing and interpreting differences In social behavior among species Is tne comparative approach (Dewsbury & Rethl lngshafer, 1973; King, 1970). Murold rodents are a group that Is particularly suited to the use of the comparative method (Dewsbury, 1974, 1978). The two murold rodent species that were chosen for comparison In this study, the monogamous Peromyscus pol jonotus Coldfield mouse) and polygamous Peromyscus manlculatus (deer mouse), are both members of the manfculatus species group of the subgenus Peromyscus. Because the majority of mammal Ian species are considered to be non-monogamous (Alexander, 1974; Crook, 1977; Kielman, 1977; Ori ans, 1969) and relatively I lttle Information Is available about mate choice In monogamous mammal Ian species, It was considered to be particularly Important that one of the species selected for comparison In the present study be a monogamous species. Although monogamy has been suggested for several rodent species, 18

PAGE 26

19 "except for .E..... pol jonotus, the data are circumstantial" (Foltz, 1981a, p. 665) and are open to more than one interpretation. Data supportive of monogamy in .E..... pol ionotus include the consistent finding that the majority of reproductively mature individuals are captured as heterosexual pairs (Blair, 1951; Foltz, 1981a; Rand & Host, 1942; Smith, 1966), and behavioral (Blair, 1951) and electrophoretic (Foltz, 1981a) evidence that pairs form long-term reproductive associations. Information about mate selection in this species was also considered to be of importance, in addition to comparative considerations, because one subspecies, the beach mouse (J:..... pol ionotus leucocephalus), is presently considered endangered. In contrast to .E..... pol jonotus, electrophoretic evidence indicates polygamy for .E..... maniculatus
PAGE 27

20 1979; Jannett, 1980; Lidicker, 1980) or indoor (Bowen & Brooks, 1978; 0-owcroft & Rowe, 1963; Getz & Carter, 1980; Hi I I, 1977; Poole & Morgan, 1976; Reimar & Petras, 1967; Thiessen & Maxwell, 1979; Thomas & Birney, 1979) seminatural enclosures. While these enclosures do not rep I icate natural conditions in many respects, they do al low the investigator to approximate some aspects of the natural setting, and al low a degree of control over experimental variables that Is generally not available in nature. Even in a seminatural apparatus, however, interactions may often be so complex that it is difficult to evaluate the effects of any single variable on a particular behavior such as social preference. This problem has led investigators to the use of even more control led situations, such as preference apparatus of various types, to evaluate the role of v2rious factors in social preference. In the typical preference paradigm an an i ma I C the "choice" an I ma I) is a I I owed to express preference by "choosing" between two or more alternative stimuli, Behavioral me~sures of preference may include factors such as the number of approaches, number of visits, duration of visits, time spent huddl ins together, mating activity, and a variety of other measures. Use of preference apparatus, in addition to al lowing more control led investigation of particular factors (e.g., f a~ il iarlty) than may be available In seminatura l apparatus, allows the experimenter to control the degree of contact between choice animals and stimulus animals. In a tether preference apparatus, for example, stimulus animals are tethered in a fixed area while the choice animal Is al lowed free access to the apparatus and may express preference through

PAGE 28

21 proximity or contact behaviors, or under appropriate conditions, mating behavior (\'lard et al., 1981; Huck & Banks, 1982; \'/ebster, \'/II Iiams, & Dewsbury, 1982). An alternative method used in preference tests is to place collars on the stimulus animals, and then place these animals in compartments with doorways of a size large enough to al low access by choice animals, but too smal I for the collared animals to pass through (Mainardi, Marsan, & Pasquali, 1965; McDonald & Forslund, 1978). Direct contact between choice animals and stimulus animals may also be prevented by simply constructing stimulus compartments or containers so that they are not accessible by the choice animal (Agren & ~~yerson, 1977; Carmichael, 1980; Carr, l'/ylie, & Loeb, 1970; Murphy, 1977; Webster, Sawrey, Wi II iams, & Dewsbury, 1982). Experimenters have also opted at times to test preference for odors from stimulus animals rather than using the animals themselves (Carr et al., 1980; Fass, Guterman, & Stevens, 1978; Gi Ider & Slater, 1978; Huck & Banks, 1979, 1980; Krames et al., 1967; Ruddy, 1980), or to restrict choice cues to olfactory cues by using anesthetized stimulus animals (Landauer, Banks, & Carter, 1977; Landauer, Seidenberg, & Santos, 1978; Murphy, 1980). While preference apparatus offer the opportunity for greater control over variables than do seminatural apparatus, the conditions under which preference is assessed do not approximate natural conditions as closely as do conditions in seminatural apparatus. With preference apparatus, therefore, one may run a greater risk of obtaining results that are misleading in respect to behavior under more natural conditions. Social preferences may, for example, sometimes be

PAGE 29

22 expressed less strongly in preference apparatus than they would be in a more natural context; one might therefore be more I ikely to falsely reject a factor as unimportant to social preference in these tests. One way to minimize this problem is to first assess a species' social behavior in more natural settings, such as in seminatural apparatus, and select factors for preference experiments on the basis of those results. Alternatively one might use results from seminatural experiments in part as a guide in interpretation of results from preference experiments. General Experimental Information This study was designed to provide data on aggression and fami I iarity as factors in the social preference of monogamous and polygamous species. Partial data are avai I able about the function of these factors in the social preference of the representative species chosen for this study, E.... pol ionotus and E.... manjculatus. Available evidence indicates that aggression may be an important factor in the social behavior of E.... manjculatus, that more aggressive males may sire more offspring than less aggressive males, and that differences in male aggressive abil lty may be important in female choice in this species. In E.... maniculatus blandus Blair and Howard (1944) found that, in experimental populations consisting of two individuals of each sex, one male would generally establish dominance over the other. The dominant male generally nested with both females more frequently than did the subordinate, and the authors were able to establish (through coat-color markers) that dominant males sired the

PAGE 30

---23 majority (19 of 21) of I ltters In their study. Dewsbury (1979, 1981c) found that male dominance In .E..... manlculatus balrdl was positively related to copulatory behavior, and that dominant males not only copulated more than subordinates, but that they also sired a larger number of offspring (Dewsbury, 1981c). Eisenberg (1962) observed that after the formation of dominance relationships between male .E..... manlculatus gambelll, females of this species that had been paired with subordinate males for two weeks prior to aggression tests generally failed to remain with their subordinate male partners and nested Instead with the dominant male. Blair and Howard (1944) studied two subspecies of .E..... pol lonotus, P. pol lonotus alblfrons and..E. pol lonotus feucocepbalus, and found I ittle evidence of aggression against conspeclflcs by Individuals of either sex. In addition al I four individuals (two males and two females) In a group were frequently found nesting together. From these observations the authors concluded that .E..... pollonotus were a very social species. Field observations, however, do not support the notion that adult E.... pol jonotus are highly social. Although E.... pollonotus are commonly found In family groups composed of a male, a female, and young (Blair, 1951; Foltz, 1979; Rand & Host, 1942; Smith, 1966; personal observations), sexually mature Individuals of the same sex are never (Smith, 1966), or very infrequently (Blair, 1951; Rand & Host, 1942) found together In the same nest. In addition Blair (1951) observed wounding In some transient and Immature Individuals and also observed, In trap and release experiments, that adult females often chased other females from nests. Smith (1967) has suggested that

PAGE 31

24 females of this species "are normally dominant over their mates and play a major role in the process of pair formation and maintenance of the pair bond" (p. 236). E.a. pol ionotus have also been observed to exhibit aggression In some laboratory tests (Garten, 1976; Smith, Garten, & Ramesy, 1975), but the conditions for these tests do not al low evaluation of the function of aggression in a social context, or as a factor in social preference. Few data are avai I able on the function of aggression and fami I iarity in the social behavior of E.a. pol jonotus, or in the social behavior of monogamous species in general. The first set of experiments in this study was designed to provide such data. These experiments were conducted in a seminatural apparatus that was designed with artificial burrows. This design takes into consideration the semifossorial habits of E.a. pol jonotus, and thereby al lows an approximation of natural conditions in this species. The semi natural experiments with E.i. pol ionotus were fol lowed by preference experiments on both E.... pol ionotus and Ea. manjculatus. These e x periments al lowed preference based on aggressive abi I ity and fami I iarity to be assessed under the same conditions for both species, and thus al lowed a direct comparison of the relative value of these factors in the social preference of these two species. The first set of these experiments examines aggressive abi I ity and fami I iarity with unrelated individuals (based on previous contact) as factors in social preference; the second experiment examines preference for siblings.

PAGE 32

25 General Methods Subjects Subjects for this study were 45 to 65 day old Individuals of two species of muroid rodent, Peromyscus pol ionotus subgriseus and Peromyscus maniculatus bairdi. The .E..... pol {onotus were laboratory-bred animals one to four generations removed from the wl Id. The parental stock was obtained from two different subpopulations In the Ocala National Forest in Florida. The first group of these animals was trapped In 1978 from road shoulders along State Road 316 between Salt Springs and Eureka. Additional animals for breeding stock were trapped in 1980 from road shoulders along U.S. Highway 19. These two populations are from the same general area as that I isted as population 25 by Selander, Smith, Suh, Johnson, and Gentry (1971). The method of capture was similar to that detailed by Foltz (1979). It is not possible to determine how many generations removed from the wild the .E..... manjculatus were. This colony was founded at the University of Florida with animals obtained from near East Lansing, Michigan, in 1970, and additional wild stock has been added on several occasions since. Animals were housed In clear plastic cages measuring 48 x 27 x 13 cm or 29 x 19 x 13 cm with wood shavings as bedding. Purina laboratory animal chow and water were provided ad I lb. Prior to serving as subjects al I animals were maintained as I itters. Peromyscus pol lonotus I ttters were weaned at 22 or 23 days of age, E.... manjcu!atus were weaned at 21 days of age. Animals that exhibited obvious physical

PAGE 33

26 defects, such as extensive tall wounds or missing tai Is, were not selected for study. Animals of both species were maintained on a reversed 16L:80 photoperiod. Al I adaptation and testing were conducted during the dark portion of the photoperiod. With the exception of observations conducted in the seminatural apparatus, which was in a separate room, al I studies and adaptation periods were conducted in the~ pol ionotus colony room. Procedural detai Is specific to particular studies are described in the methods sections of those studies. Apparatus Seminatural apparatus The seminatural apparatus was a large square Plexiglas arena 125 cm on a side and 46 cm deep. The sides of this arena were constructed with 1/4 inch Plexiglas and the floor was constructed with 1/2 Inch ply1-,ood and painted grey. The arena was partitioned, with four 85 cm lengths of 1/4 inch Plexiglas, into a square central area that measured 85 cm on a side and tour right angle triangular corner compartments with sides of 85 cm, 61 cm, and 61 cm {See Figure 1). Two nest boxes were attached to each corner compartment. Nest boxes were constructed with sides of 1/4 inch Plexiglas and 1/4 inch plywood backs. They measured 10 x 9 x 8 cm and had hinged Plexiglas I ids to provide access for removal of animals and cleaning. A 3.2 cm diameter hole cut in the front of each nest box provided access for the animals. In each corner compartment two matching 3.2 cm diameter holes, cut in the sides of the apparatus, 45.5 cm from the corner and 1 .5 cm from the floor, provided access to the nest boxes. The front of

PAGE 34

-, I I / I / -l/ I --I I I 27 -, ...... ' I I ---------i I ( \ I / I I I } \ I\ "'--' ,, ,, \ \ I\ I \\ I I\ I I \ I I l \ Vl :::::i I ,0 s.. I ,0 I 0. 0. I c:.:: I ,I I I ,0 E s.. I :::::i I u E ,0 u s::: rE I 0 QJ (/) ,,, -r'-1 ....... I I Lu O::'. I I I ::::> c.!J E ...... LI.. I u I I a) I I I

PAGE 35

28 one of the nest boxes for each corner compartment was connected with sf I Icon cement directly to the side of the apparatus In I lne with one of these holes. The other nest box In each corner compartment was connected to the second opening by means of a 48 cm length of Tygon polyethylene tubing with an internal diameter of 2.5 cm and an external diameter of 3.2 cm, and thus formed an artificial burrow. Sil Icon cement was used to attach one side of the nest box to the apparatus and to connect the tubing to the openings for the nest box and the apparatus. Animals could gain access from the corner compartments to the central area of the apparatus through 3.2 cm diameter holes centered on and 1.5 cm from the bottom of the partition which formed the compartment. A 2.5 cm hole 3 cm from the right angle corner and 2 cm from the floor of the apparatus provided access for the drinking tube of a water bottle. The seminatural apparatus was In a room separate from the colony room but maintained on a 16L:8D photopericd Identical to that maintained in the colony room. The apparatus was i I lumlnated In the I lght phase of the photopericd by tour 75-watt incandescent-white bulbs and two 60-watt red bulbs, each suspended three feet above the floor of the apparatus, and during the dark phase of the photoperiod by the two 60-watt red bulbs alone. Behavioral measures were recorded by means of a 20-channel Ester! lne-Angus event recorder. The behaviors exhibited by each group of animals, during their four days In the semlnatural apparatus, were also recorded on videotape using a Hitachi CCTV low I lght television

PAGE 36

29 camera, and a Panasonic time lapse VTR video tape recorder set on a 72 hour record mode. Preference apparatus The preference apparatus was a three chambered rectangular box with a hinged I Id; It was constructed of 1/4 Inch Plexiglas and measured 44 x 21 .5 x 20 cm {Figure 2), The Inside measurements of the two end chambers were 10 x 21 .5 x 20 cm. These chambers were open to the central area through a 7 x 7 cm opening. The end chambers were designed to accommodate smal I removable "choice chambers" which measured 10 x 8 x 6 cm. A "stimulus box" with an inside measurement of 8 x 7 x 8 cm was attached to each end chamber, and was open to It through a 6 x 5 cm opening. When choice chambers were placed In the end chambers, therefore, one end of the choice chamber was accessible from the central area, while the other end was open to the stimulus box. A hardware cloth screen lnstal led In the opening to the stimulus box and a second three-sided piece of hardware cloth which fit the Inside of the stimulus box provided a "double screen" between the choice chamber and the stimulus box. A bank of three red-sensitive photocel Is {peak response at 735 nm), wired In a series behind each choice chamber, registered entries to the chamber. The I fght sources for the photocel Is were 60-watt red I ight bulbs placed 27 cm in front of the apparatus and directly in front of the bank of photocel Is. Each photocel I was attached to the end of a tubular 4.3 cm piece cut from a 12 x 75 cm disposable plastic culture tube. The outsides of these tubes were painted black; this In effect columnated the I lght to the photocel Is. The photocel Is were

PAGE 37

,-----' ' ' \. \. \. \. \. ;--------\ \ \ \ \ ___ \ -\-\ --\ \ \ \ \ \ \ \ \ \ \ 30 l/1 ::, +-' ro !,.. ro 0.. 0.. c::i: (lJ u C: Q.) !,.. (lJ 4(lJ !,.. 0.. N w 0:: :::> c.!l ....... LL.

PAGE 38

RELAY RACK POWER SUPPLY POWER SUPPLY CHOICE CHAMBER Q~ RED + + LAMP \ PHOTOCELLS (3) COUNTERS NO I o CONTACTS louT~o lolololol2l 1v1s1rs I )r---tl--. I o lololol 3 lol I DURATION OUTPUT Q) NC I CO~TACTSr--+----~ RECYCLING TIMER I RELAY '-----+Sa EVENT RECORDER FIGURE 3 Diagram for Preference Apparatus w

PAGE 39

32 situated such that In order to register a visit to the choice chamber, an animal had to be completely Inside the chamber, and at least partially In the half of the chamber closest to the stimulus animal. Each bank of photocel Is was wired In a series with the col I circuit of a 10,000 ohm, 24 VDC DPDT relay (see Figure 3). These relays were powered through output from a variable power supply set for a continuous output of 26 volts. One of the normally closed circuits of each of these relays was wired Into the pen circuit of an Ester! lne Angus event recorder; this provided a permanent record of entries Into each choice chamber. Output from another normally closed circuit of these relays was used to control a second set of relays on a relay rack. Two banks of Sodeco counters received Input through the normally open contacts of these relays. The first bank of counters was wired In a series to pulse formers and recorded the number of visits to each chamber regardless of visit duration. Input to the second bank of counters was regulated by means of a recycling timer set to produce pulses at 1/3 of a second. These counters recorded the total duration of visits to the nearest 1/3 of a second. Session duration was automatlcal ly control led via another timer (not displayed) which control led the input to the recycl Ing timer and counters. Aggression apparatus The "aggression arena" was constructed from a large 48.5 x 38 x 20 cm plastic cage. Two 3.2 cm diameter holes were cut in the two longer sides of the cage centered 25.5 cm apart and 3.5 cm from the bottom. SI I Icon cement was used to form a gasket around each hole. Matching holes and gaskets were placed on one side of two 48 x 27 x 13

PAGE 40

33 cm plastic cages. The larger cage and two smaller cages could then be connected by 6.5 cm lengths of Tygon polyethylene tubing (Internal diameter of 2.5 cm and external diameter of 3.2 cm) to form the "aggression apparatus" (See Figure 4). During adaptation procedures the aggression arena and smaller cages were connected with unobstructed lengths of tubing; a piece of metal screen In the center of each length of tubing prevented animals from travel Ing through the tubes during tests. A 1/4 Inch 53.5 x 43 cm Plexlglas I Id was placed over the large cage, and wire cage I ids over the smaller cages, while testing was conducted.

PAGE 41

E u CX) r<) f E u C\I r r ,J "' r 34 r.-25.5cm--j 48.5 cm .-,-1J J 48 cm "' FIGURE 4 Aggression Apparatus ., ., "' , .. _,,,

PAGE 42

SECTION 111 EXPERIMENTS Semjnatural Experiments This section is divided into three major subsections; the three sets of experiments that comprise this study are each described within separate subsections under the headings of Seminatural Experiments, Aggression and Fami I iarity Preference Tests, and Sib I ing Preference Tests. Each of these subsections begins 1-lith a brief introduction to the experiments in that subsection, and specific information on subjects and procedures for these experiments. This information is fol lowed by the results of these experiments and a brief discussion of the results. The results of al I three sets of experiments in this study are discussed together, in the context of the ecology of .E...a. pol ionotus and E.... maniculatus and theoretical considerations, in the General Discussion section. Introduction This experiment was designed to provide information on aggression and familiarity as factors in the social behavior and mate selection of E.... pol jonotus. (Simi I iar types of data already exist for E.... maniculatus: Blair & Howard, 1944; Dewsbury, 1979, 1981c: Eisenberg, 1962.) Although it is difficult to establish the relevance of factors in social preference per se with seminatural observations, such data can provide an indication of the functions a factor may serve in 35

PAGE 43

36 nature, and can provide Indications of whether a factor may be of importance In social preference. Subjects Subjects were 40 male and 40 female .E.... pol ionotus. Prior to serving as subjects, animals were maintained as previously described In the section on general methods. Subjects were selected using the criteria described In the general methods, and the additional criterion that the animals within any group had no common grandparents. Procedure In order to better separate and evaluate the roles of aggression and famll iarity In the social behavior of .E.... polJonotus animals were observed under two different experimental conditions, the "paired" condition and the "single" condition. Twenty animals of each sex were assigned to either the single condition or the paired condition. Animals In each condition were divided Into 10 groups; two animals of each sex were assigned to each group. Each of the 10 groups of animals in each condition, single or paired, were treated separately. Animals within each group were I lghtly anesthetized with ether and shaved In one of the fol lowing four patterns: (1) band shaved around the neck; (2) band shaved around the middle; (3) band shaved at the rear; (4) no shaved area. Shaving was performed one day prior to beginning the first experimental manipulation. Approximately equal numbers of males and females received each shave pattern. Subjects under both the single and paired conditions were exposed to a series of three different experimental manipulations. These manipulations, in order,

PAGE 44

37 and their durations were "nest building," 4 days; "semi natural isolation," 3 days; and "seminatural interaction," 4 days. During the four-day nest bui I ding period animals were housed in 48 x 27 x 13 cm plastic cages on San-i-cel bedding. Animals in the single groups were housed individually; animals in the paired groups were housed as two separate pairs of opposite-sexed animals. Three 2-inch square "Nestlets" (Ancare Corp.) were provided as nesting material in each cage. The type of nest bui It was assessed just prior to the beginning of the dark period on the next 4 consecutive days. Nests were rated as one of three types: (0) no nest; (1) platform nest; (2) covered nest. The seminatural isolation period began in the first dark phase which fol lowed the nest building period. Animals were transferred from the colony room to the room containing the seminatural apparatus approximately 15 min after the beginning of the dark phase. Animals from single groups were each placed individually in corner compartments, with animals of the same sex in compartments diagonally opposite each other. Animals from paired groups, which had been maintained as pairs during nest building, were transferred to the seminatural apparatus in the same paired relationship. Pairs were placed in corner compartments of the apparatus diagonally opposite each other. The opening from each corner compartment to the central area was closed with a sol id black rubber stopper so that animals were restricted to the compartment in which they had been placed. The floor of the central area and of the corner compartments had been covered with San-i-cel to a depth of approximately 1 .5 cm; each corner

PAGE 45

38 compartment also contained three Nestlets, and food and water was avai I able ad I lb. Animals were maintained in the corner compartments for 3 days. Activity during this entire pericd was videotaped. Each pair of animals In the paired groups was also observed for three alternate 10-mlnute periods during the dark phase on the day the animals were Introduced, and on the fol lowing two days. On the first day, observation was begun as soon as al I animals had been placed In the apparatus. On each of the fol lowing 2 days one of the pairs was designated as the first pair to be observed, and the first period of observation was begun when the members of that pair had emerged from their burrow. The behavioral and aggressive measures that were recorded were similar to categories described by Al I In and Banks (1968) and Colvin (1973). Measures were recorded by means of a 20-channel Esterl lne-Angus event recorder. The measures, and definitions of each, were as fol lows: Approach Attack Chase Scored when an animal came within one and one-half body lengths of another while oriented toward it. Scored when one animal lunged at or charged another but did not pursue the other or Initiate vigorous biting behavior. This behavior could be accompanied by a single bite or attempts to bite. Scored when one animal pursued another.

PAGE 46

Fight Rough-and Tumble-Fight Displacement Submissive Aggressive Digging 39 Scored when one animal 1 s attack on another escalated to vigorous biting behavior by both indivlduals. Generally the Initiator wou Id knock the other an i ma I over, or ro I I to one side with the other animal clenched in Its jaws while shaking Its head, often simultaneously clawing with the rear claws. Fighting often resulted after one anlmal did not retreat when attacked, but rather attempted to defend itself or at the end of a chase If the pursuing animal caught the other. A very vigorous form of fighting; rough-and tumble fights were only scored when both animals were tumbl Ing end over end whl le attempting to bite and claw each other. Scored when one animal retreated upon another anlmals approach. Scored when one anlmal, upon approach or attack by another, either rolled over on its back, or reared back upon its hind legs with its nose pointed up, and made no attempt to defend Itself. Both approach and submission or attack and submission were scored for each encounter~ This was a very vigorous form of digging behavior much more Intense than the type of digging these animals have been observed to perform in an isolated test (Webster, Wil Iiams, Owens, Geiger, and Dewsbury; 1981). Although this behavior was not generally directed toward an opponent, It was very similar to that described by Al I in and Banks (1968). Under both experimental conditions, single and paired, the Isolation period was fol lowed by the semlnatural interaction period. Ten min prior to the first dark phase in this period the rubber stoppers were removed from the partitions between each corner compartment and the central area. Behavioral and aggressive

PAGE 47

40 interactions between animals, as defined above, were recorded during the first hour of the dark phase for 4 consecutive days. Nesting relationships were recorded each day, for the last 3 of these 4 days, 20 min prior to the beginning of the dark phase. An animal was defined as having nested with another if it was found in the same nest with the other, and videotape records verified that it had not switched nests between the period extending from after the first 1/2 hr of the preceding I ight phase to 1/2 hr prior to the nest check. Activity during the entire isolation and interaction stages was videotaped. The seminatural apparatus, including the artificial burrows and nest boxes, was thoroughly cleaned with a solution of Sterigent (a deodorant and disinfectant soap) before each group of animals was introduced to the apparatus. Water bottles were also cleaned and refilled, and fresh San-i-cel, food, and Nestlets were placed in the apparatus. Results Peromyscus pol ionotus appeared to adapt very quickly to the seminatural apparatus in general, and to the artificial burrows in particular. Al I but five of the 40 individuals in the paired condition entered and explored the artificial burrows within the first hour of observation, and al I except two pairs of the 20 pairs observed In the paired condition had constructed at leat a rudimentary nest in the burrow by the end of their first day in the apparatus. Individuals in the paired or single groups were only infrequently observed nesting in the alternate nest box, although this box was frequently used for feeding and as an escape when individuals were attacked. Aggressive

PAGE 48

41 relationships between Individuals In each group appeared to remain fairly stable over their four days together In the semlnatural apparatus. In al I 10 sing le groups, and in seven of the 10 paired groups, the Individual with the highest total frequency of aggressive behavior (sum of al I attacks, chases, fights, and rough-and-tumble fights) on day one, sti I I exhibited the highest frequency of aggressive behavJor on day four. In the other three paired groups the Individual that exhibited the highest frequency of aggressive behavior on day two also exhibited the highest frequency on day four. Each animal In a group could potentially Interact with twice as many opposite-sexed individuals as same-sexed individuals. To adjust for this bias, the mean value of any measure of an animal's Interaction with both opposite-sexed Individuals, rather than the total, was used in analyses Involving opposite-sexed Individuals. Several significant differences In aggression were apparent In comparisons between males and females in both the paired and single conditions. Males were more aggressive than females in a statistically significant larger number of groups by al I measures except the number of rough-and-tumble fights (designated in tables as r&t fights; see Table 1). Within the sing le condition males were the more aggressive sex In a significantly larger number of groups by al I measures except the number of rough-and-tumble fights and the duration of rough-and-tumble fights. Within the paired condition males were the more aggressive sex in a slgnlflcantly larger number of groups for the measures of number of attacks, number of fights, duration of fights and number of approaches. There was no measure, for either the paired or

PAGE 49

42 Table 1 Comparison of the Number of Groups In Which Males or Females Were More Aggressive Total (N=20) Pa I red (N=lO) Measure Male Female Male Female No. of attacks 19 1*** 9 1* No. of fights 17 2*** 9 1* Durati6n of fights 18 2*** 9 1* No. of chases 17 3** 8 2 Duration of chases 17 3** 8 2 No. of r&t fights 13 5 6 2 Duration of r&t fights 15 3** 8 2 No. of approaches 19 1*** 10 O** No. of displacements 15 4* 7 3 Al I durations are In seconds. Sign test 2-tall *~<.05 Single CN=lO) Male Female 10 O** 8 1* 9 1* 8 1* 9 1* 7 3 7 1 9 1* 8 1*

PAGE 50

43 single condition, for which females were more aggressive than males in a larger number of groups. Males In general also exhibited higher total levels of aggression than females by al I measures (see Table 2). Males, in both single and paired groups, exhibited a higher frequency of attacks, fights, chases, displacements and approaches than females. They also exhibited longer durations of chases and fights than females In both types of groups (see Table 3). Although differences In the total amount of submissive behavior exhibited by males and females across both groups were not statistically significant (1=1.28, .d.f=19, .Q.>.05), males had more submissive behavior directed toward them than did females (palred-1=2.71, .d.f.=19, ,Q_<.05). Because aggressive digging was not Immediately recognized as a possible correlate of aggresslo~ It was not recorded for the three lnltial paired groups. It was recorded for al I subsequent paired and al I single groups. No significant differences in the frequency, duration, or mean duration of aggressive digging were apparent in comparisons between paired and slngle animals. Males displayed higher levels on al I of these measures than did females, with the exception of the comparison of the average duration of aggressive digging for slngle animals. High-aggression males (those In each group with the highest total frequency of aggressive behavior) displayed a higher frequency of aggressive digging than low-aggression males (palred-1=2.30, .d.f.=16, ,Q_<.05). The difference between high and low-aggression animals In the level of aggressive digging they dlsplayed may be due In part to differences In the response of these two classes of individuals to

PAGE 51

44 Table 2 Ccmparlson of Total Aggression Within Groups by Males and by Females in Both Paired and Single Conditions Male Female Measure Mean
PAGE 52

Measure No. of ettacks No. of tights Total duration of fights M e an duration of fights No. of chases Total duration of cheses Mean duration of choses No of r&t fights Total duration of r&t fights Mean duration of r&t fights No. of epproaches No. of displacements No. of 1199resslva digs Total duration of 1199resslve digging Mean duration of ~gresslve digging All durations ore In seconds. Analysis of Vorlonce 2-tel I Table 3 Total Level of Aggression by Males and Females in Paired and Single Groups Tote! (Polred end Single) Pelred M.c1L_ F11m!!le Male Female Meen (SEl Meen (SEl F(I 59) Meen u, F(l ,29) Mean (SE) Mean (SE) F( 1,29) 5.17 1 23 .70 5.94 4.05 1.08 5.79 8.00 2.36 1.25 .79 6.31 ** 6.31 ** 11.20 3.67 1.45 .96 5 .82 .85 .BB .16 .22 .10 11.99 11 6.10 56.00 13.40 10.10 3.77 8.66* 11 6 .69** 332.75 84.32 62.85 24.64 7 .64 11 4.06 4.07 .64 3 07 .69 1.02 1.94 3.50 1.52 .60 .30 3.33 ,68 6.80 3.20 .70 .39 3.43 1.78 .79 .22 .22 .10 5.25 7.21 .. 29.30 6. 70 8.05 2.09 9.63*** 3.57 4.60 3.67 .80 .41 6.67*' 7,23 10.47 4.27 .60 .27 5.71 ,.55 1 20.68 8.61 .85 ,39 4.81 1 9. 78 1 ** .98 .29 .35 .16 3 14

PAGE 53

46 noises within the apparatus. High-aggression animals often Investigated noises made by other Individuals In the apparatus. Low-aggression Individuals generally Ignored these noises or retreated from them. Low-aggression individuals that attempted to dis, therefore, In effect increased the probabi I lty of attack by high-aggression Individuals, whereas high aggression Individuals dug without Interference. Individuals directed more aggression toward same-sex than opposite-sex Individuals In both the paired and single conditions (see Tables 4 and 5). Males in both single and paired groups directed more fights and rough-and-tumble fights, and longer durations of these behaviors, against other males than against females. Females in both single and paired groups directed more attacks toward same-sexed than opposite-sexed Individuals. Males and females in both types of groups directed more chases toward same-sex than opposite-sex Individuals. Although many of the differences In aggression between sexes were significant, and many significant differences were also found in the level of aggression directed at same versus opposite-sexed Individuals, the overal I levels of aggression displayed by animals In the single and paired conditions were very similar (means and standard errors were presented In Table 3). Animals In the two conditions displayed significant differences on only two of the aggressive measures: paired animals displayed longer average durations cf fights with same-sexed Individuals and a greater number of approaches to same-sexed Individuals than did animals In the single condition (1=2.12, .Qi.=78, ~<.05; and 1=2.10, .Qi.=78, ~<.05 respectively).

PAGE 54

Table 4 Aggression Against Same-Sex and Opposite-Se x in Paired Groups Totel Males Females Same-Se x Opposite-Sex S a me-Sex Oeeoslte-Sex Same-Se x ...Qfil?_oslte-Sex Measure Mean CSE> Mean CSE) t Mean CSE) Mean (SE> t Mean (SE) Mean (SE) t N o. of attacks 6.63 1.66 3.88 1.04 2 .78*** 9.75 2.94 6.43 1.81 1.85 3 50 1.27 1.32 68 2.49* N o. of f I ghts 3.05 .75 .56 20 3.62**** 4 50 1.21 1.02 .38 3.17*** 1.60 .80 .10 ,05 1.88 Duration of fights 5.40 1.24 1.04 .43 3.92**** 8 05 2.02 1.88 .81 3.46*** 2.75 1.24 .20 .11 2.04 -..J Me an duration of fights 1.01 .22 .64 .16 1.60 1.40 .31 .88 .23 2.06 .63 .30 .40 .22 .57 N o. of chases 24.80 6.88 5.59 1 .52 3.22*** 40.60 12.30 9.80 2 68 2.82* 9.00 4.10 1.38 6 6 2.12* Durati o n of chases 147 .30 41 .80 29.33 9.74 3.09*** 242.35 74. 78 52.00 18.00 2,7211 52.25 25.09 6.65 3.33 1.95 Mean duration of chases 3.23 .47 2.67 .44 1.30 3.91 .67 3.70 .52 .34 2.54 .62 1.63 .63 1.53 No. of r&t fights 1.00 .29 .04 .02 3.40*** 1.45 .46 .03 .03 3.17*** .55 .33 .05 .03 1.55 Duration of r&t fights 2.65 .87 .08 .05 2.96*** 3.45 1.08 .03 .03 3.19*** 1.85 1.37 .13 09 1.26 Mean duration of r & t fights .88 .24 .15 .09 2.91** 1.27 .38 .05 .05 3.19*** .49 .26 .25 .18 .18 N o. of a pproaches 6 53 .98 9.28 I. 71 1.59 7.40 1.47 13. 70 2.98 2.03 5.65 1.31 4.85 1.01 .69 No. o f displ a ce m ents 2 20 .81 1.60 .45 .83 3.30 1.57 2.45 .83 .61 1.10 36 75 .24 .85 Al I durations ere In seconds. Opposite-sex means are mean values per opposite-sex lndlvlduel, Palred-1 Total .d.f.=39 Male end Fem a le .d.f.=19 2-tal I *Jt<.05 **,t<,01 ***J2<.005 ****Jl.<.001

PAGE 55

Table 5 Aggression Against Same-Sex and Opposite-Sex in Single Groups Total Males Females Same-Sex Oeeoslte-Sex Same-Sex 012120s lte-Sex Same-Sex __QQl?.os I te-Sex Measure Mean (SEl Mean ( SEl t Mean (SEl Mean (SEl t Mean (SEl Mean ISEl t No. of attacks 5.25 1.23 4.18 1.16 1.60 8.50 2.21 7.60 2.05 .60 2.55 .83 75 .25 2.23* OJ No. of tights 3.53 1.12 .55 .21 2.81** 5.85 2.00 1.08 .40 2.48* 1.20 76 .03 .03 1 .59 Duration of fights 4.45 1.55 .94 .41 2.46* 7.60 2.84 1.80 .79 2.16* 1.30 .83 .OB .08 1.58 Mean duration of fights .49 .10 .42 .12 .74 .78 .16 .68 .18 .58 .21 .10 .15 .15 .45 No. of chases 19.88 4.83 6.59 1.86 3.43**** 32.00 8.40 12.00 3.31 2.86** 7. 75 3.13 1.18 .46 2.30* Duration of chases 147.98 37.60 24.91 6.93 3,73HH 241 .55 66.11 45.60 12.20 3.34*** 54.40 22.59 4.23 8.23 2.31* Mean duration of chases 3.45 .66 2.37 .34 1.86 4.43 1.05 2.88 .46 1.74 2.48 .76 1.85 .48 .82 No. of r&t fights 1.80 .72 .13 ,08 2.44* 3.05 1.37 .23 .15 2.16* .55 .29 .03 .03 1. 79 Duration of r&t fights 3.15 1.41 .30 .18 2, 19* 5,65 2.71 58 .34 2.03 .65 .38 .03 .03 1.65 Mean duration of r&t fights .48 .12 .33 .16 1.30 .74 .20 .61 .30 .62 .22 .10 .05 .05 1.80 No. of approaches 3.70 .92 7.49 1.60 3.06*** 5. 70 1.55 11 .80 2.83 2.70* 1.70 .80 3.18 .80 1.85 No. of displacements .88 .29 .91 .26 18 1.50 51 1.55 .46 .13 .25 .20 .28 .13 .15 Al I durations are In seconds, Opposite-sex means are mean values per opposite-sex Individual. Palred-1 Total .a_ta39 Male end Female .a_t-19 2-tel I *D.< .05 **J>.<.01 ***si<.005 ****si<.001

PAGE 56

49 Comparisons of aggressive measures between the two conditions within each sex yielded significant differences for females only (means and standard errors were presented In Tables 4 and 5). Paired females exhibited a greater number of approaches to same-sex individuals and a greater number of displacements of same-sex individuals than did single females <1=2.57, .d.f=38, Q<.02; and 1=2.08, .d.f=38, Q<.05, respectively). The various measures of aggression recorded tended to be correlated with each other. The total frequency of attacks, chases, fights, and rough-and-tumble fights were correlated within each sex for both paired and single groups, as were the duration of chases, fights, and rough-and-tumble fights. The frequency of approaches was correlated with the number of chases for males and females in both conditions and with the number of attacks for paired males and females and single males (see Table 6). The amount of submissive behavior directed toward single females was correlated with the frequency and duration of fights (Pearson correlation, c=.724 and c=.798, respectively, Q<.001) and the frequency and duration of rough-and tumble fights (Pearson correlation, c=.704 and .800, respectively, Q<.001). Submission was also correlated with the total frequency of approaches for paired females and single males (Pearson correlation, c=.444 and c=.515, respectively, Q<.05). Frequency of aggressive digging was correlated with the total frequency of aggressive behavior (combined frequencies of attacks, fights, chases, and rough-and-tumble fights) for paired males and females (c=.638, Q<.05, and c=.845, Q<.001 respectively) and single males
PAGE 57

Table 6 Pearson Product-Manent Correlation of Aggressive Measures for Males and Females In Paired and Single Groups Paired Single Measure Male Female Male No. of attacks and chases .875**** .973**** .889**** No. of attacks and fights .570** 735**** .629*** No. of attacks and r&t fights .751i-*H .765**** .389* No. of attacks and approaches 787**** .564** .719**** No. of attacks and dlsplacements .580*** .494* 797**** No. of fights and chases 790**** .842**** .858**** No. of fights and r&t fights .686**** 964iC *** .890**** No. of fights and approaches .421 .254 .257 No. of fights and displacements .843**** .389 .327 No. of chases and r&t fights 723**** .856**** .643**** No. of chases and approaches 749**** .473* .609*** No. of chases and displacements 799**** 471 .690**** No. of r&t fights and approaches .469* .265 .045 No. of r&t fights and dlsplacements .428 .387 .094 No. of approaches and displacements .468* .713**** .898**** Duration of chases and fights .670**H.865**** .843**** Duration of chases and r&t fights .753**** .823**** .689**** Duration of fights and r&t fights .750**** .847HH .914**** All durations are In seconds. Correlations based on total frequencies and durations. N=20 2-tal I test *~<.05 **~<.01 ***~<.005 ****~<.001 Female .901**** 714*Ha .659**** .226 .474* 7 55**** .898**** u, 0 .321 .496* 721 **** .322 .337 .226 .407 .073 779**** 728**** 933****

PAGE 58

51 aggressive digging was correlated with total frequency of aggressive behavior for single males (c=.527, Q<.05) and paired females (c=.845, Q<.001). An animal's weight did not appear to be an important factor In aggressive Interactions. Only the correlation between weight and the frequency of rough-and-tumble fights In single females was statistically significant .05; females: c=.087, Q>.05) or total frequency of aggressive Interactions (males: c=.015, Q>.05; females: c=.118, Q>.05). Pairing did, however, have some effects on later levels of aggression. Males In paired groups were less aggressive to the females with which they had previously been paired than to females with which

PAGE 59

52 they had not been paired by the measures of frequency and duration of chases (one-tat I palred-1=2.18 and 2.22, respectively, M=19, ~<.05). Males also exhibited a higher frequency of approach to females with which they had been pal red (one-tat I palred-1=1 .78, _g_f=19, ~<.05). None of these comparisons were significant for females (Number and duration of chases, 1=.38 and .76 respectively, approach; 1=1 .08, M=19, ~>.05). A problem arises when one attempts to compare different classes of anlmals as to their levels of aggressive interactions with one another. The problem is that the total amount of contGct between different classes of animals may vary. For example, If females tend to avoid other animals, but males do not, lndlviduals would have more opportunities to be aggressive to males than to females. A difference, therefore, In the level of aggression an individual expresses toward Individuals of one class versus another may reflect a true difference In the frequency of aggression, or a difference in the frequency of access to Individuals of the two classes. One method of gaining a clearer understanding of the level of aggression, and differences in It between classes of individuals, Is to construct a scale or index for comparisons which accounts for differences In frequency of contact. An "aggressive Index" was calculated for this study by dividing the total frequency of al I aggressive encounters Initiated by an animal (frequency of attacks, chases, fights, and rough-and-tumble fights) toward any other class of Individuals by the total number of contacts initiated by that animal toward that class of Individuals (total aggressive encounters plus the frequency of approaches and

PAGE 60

53 displacements). Although there may be qualitative differences in approaches which elicit displacement or submission and those which do not (for example an aggressive individual may signal its status through adopting a particular posture), no means was avai I able in the present study to detect these cues. Therefore displacements or approaches with submission were classed as contacts without aggression for purposes of constructing the index. No significant differences were apparent between paired and single groups, or in comparisons between males or females of these groups, in the total frequency of contacts or the frequency of contact with same-sexed or opposite-sexed individuals (see Tclbe 7). Single females did, however, have a significantly higher overal I aggressive index (frequency of al I aggressive behaviors divided by frequency of al I contacts) and a higher aggressive index against opposite-sexed individuals than paired females. The total frequency of contact was significantly higher for males than for females in the paired and single conditions. Although the overal I aggressive index was significantly higher tor paired males than paired females, the difference between single males and females was not significant (see Table 8). Paired males and females and single males al I displayed a significantly higher frequency of contact with same-sexed than opposite-sexed individuals. Whereas both paired males and females displayed a significantly higher aggressive index against same-sexed than against opposite-sexed individuals, this comparison was not significant for single males or females (see Table 9). Paired males,

PAGE 61

Table 7 Aggressive Index and Frequency of Contact with Same-Sex and Opposite-Sex Animals for Paired and Single Conditions Total (Males and Females) Male Female Paired Slni!..!._ Paired Sing le Paired Sing le Measure Mean
PAGE 62

Table 8 Aggressive Index and Frequency of Contact for Males and Females Total (Paired and Single) Paired Sing le u, Male Fe m ale M ale Female Male Female u, Meas u r e M ean (SE) M ean (SE) FCl,59) Mean (SE> M e an (SE) FC 1,29) Me an ( SEl M e an CSE) F ( 1,29l l'.! C !;J C !l SSl~a .58 .05 .39 .06 15 51**** .51 .06 .27 ,06 7,49* .63 .07 .51 .09 1.30 Frequency of C ont a cts 129 48 20.31 31.58 6.35 17.07*** 133,85 30.67 38.30 10.73 7.08* 125.10 27.40 24.85 6.76 10,09*** Analysis of Variance 2-tal I *ii.< .05 **ii_<.01 ***ii<,005 ****ii<.001

PAGE 63

Table 9 Aggressive Index and Frequency of Contact for Males and Females with Same-Sex and Opposite-Sex Individuals Total Male Female Same-Sex Opposite-Sex Same-Sex Opposite-Sex Same-Se x Opposite-Sex Measure Mean (SE) Mean (SE) t Mean (SE) Mean
PAGE 64

57 but not paired females, exhibited a lower aggressive index against pair members than against opposite-sexed non-pair member (two-tai I 1-test, .Qf=19, males and females respectively: 1=2.25, Q<.05; i=l .41, Q>.05). The frequency of nesting arrangements, for days on which complete nest data were ava i I ab I e, is presented in Tab I e 10. It is of interest that two ani m als of the same sex nested together only once without an opposite-sexed animal also present. Animals nested as two opposite sexed pairs en over 1/3 of the days for which data were avai I able and almost another 1/4 of the nesting arrangements observed included one opposite-sexed pair. Only data on nesting behavior for days on which nesting relationships were known for al I individuals in a group were analyzed statistically. Nest data were avai I able tor al I but one paired and one single group. Three days of nest data (the total possible) were avai I able for two of these nine paired, and seven of these nine single group~ Two days of data were avai I able for six paired and two single groups, and only one day of data was avai I able for one of the paired groups. The mean number of days of data available for nine paired and nine single groups were 2.11 days and 2.78 days, respectively. The analyses of nesting behavior presented in the tables are based on the "\vi lcoxon-test" (Siegel, 1956). Analysis of nesting behavior by this test in the present study may give more "weight" to observations from groups for which more days of data are avai I able. Significant comparisons in the tables that were not also significant by the "sign test" (Siegel, 1956) are noted in text. Animals generally nested with opposite-sexed rather than same-sexed animals. Differences in nesting

PAGE 65

58 Table 10 Frequency of al I Possible Nesting Arrangements Paired Single Total Groups Groups All four together 4 1 3 Two opposite-sex pairs 15 7 8 Two males, one female 3 3 0 Two females, one male 6 4 2 Two males 0 0 0 Two females 1 1 0 One opposite-sex pair 12 2 10 None together 3 1 2 Only days on which al I anlmals could be accounted for are included (Total number of days=44).

PAGE 66

Table 11 Nesting Frequency with Same vs. Opposite Sex Individuals Total Male Same Opposite Same Opposite S e x Sex Sex S e x Mean(SE) Mean CSE) N z Mea n CSE) Mean CSE) Al I an I mal s .54 .10 1.01 .08 53 4.18**** .39 .10 1.03 .11 Paired animals .64 .13 .86 .08 24 1.29 .44 .12 .89 .13 Single animals .44 .15 1.17 .12 29 4.51**** .33 .16 1.17 .19 Sa m e-sex frequency= total nesting frequency with same sex. Opposite-sex frequency= (total nesting frequency with opposite sex)/2. N=num be r of non-tied observations. WIico x on I-tall *R<.05 **R<.01 ***a < .005 ****a<.001 Femal e Same Opposite Sex S e x N z M ean(SE) Mean ( SE) 23 4.20**** .69 .17 1.00 .10 8 2 .52** .83 .23 .83 11 15 3.41**** .56 .26 1.17 .17 N z (Jl I..O 30 1 .86* 16 .10 14 2 .98***

PAGE 67

Table 12 Nesting Frequency with High-Aggression vs. Low-Aggression Animals of the Opposite Sex Total Male Female O'\ 0 High Low High Low High Low Aggression Aggression Aggr e ssion Aggression Aggression ~resslon ~lean (SE) M e an ISEl N z Mean I SE l Mean (SE) N z Mean ISEl Mean (SE) N z All animals 2.47 .21 1.58 .21 21 3.39**** 2.33 .26 1.67 .31 9 2.07* 2.61 .33 1.50 .27 12 2 .67**** Paired animals 2.11 .24 1.33 .20 8 2. IO* 2 00 .29 1.33 .29 4 1.46 2.22 .40 1.33 .30 4 1.46 Sin g le an i mals 2.83 .32 1.83 .36 13 2 69*** 2.67 .41 2.00 .55 5 1.48 3.00 .50 1.67 .47 8 2.24* N = number of non-tied observations. WI lco x on 1-tal I *l).<.05 ***l).<.005 ****12<.001

PAGE 68

61 frequency with same and opposite-sexed animals were significant for al I comparisons except paired animals in general, and paired females (see Table 11). (By the sign test the comparison for al I females was also non significant, ~=10). In general animals also nested with high-aggression rather than low-aggression animals of the opposite sex (see Table 12). This was true for animals in paired groups and single groups, and for males and females. The finding of non-significance for comparisons within paired and single groups, except single females, may be due to the smal I number of non tied observations avai I able for comparison. (By the sign test comparisons for paired animals and males in general were also non-significant, ~=2 for both comparisons). Total frequency of aggression was correlated with frequency of nesting with opposite-sexed individuals for paired males and single males (Pearson correlation, r_=.710, Q<.001 and r.=.519, Q<.05 respectively) but not for paired or single females (,e=.066 and r.=.219 respective I y, Q>.05). Animals did not nest more frequently with fami I iar individuals. Comparisons based on al I paired animals, males, or females were al I non-significant (Wilcoxon, N=number of non-tied observations: al I animals, H=24, z.=1.24; males, i:J.=10, z.=1.22; females, i:J.=14, z.=.60). Neither the number of days pairs had bui It nests together during the nest building stage, nor the average type of nest bui It, was correlated with nesting frequency with pair members (Pearson correlation, nest days, r.=.395; nest type, r.=.250). Discussion These seminatural observations provide evidence that aggression is I ikely to be an important factor in social interactions in .E....

PAGE 69

62 pol jonotus. As predicted of the behavior of monogamous species (Kielman, 1977) frequent aggression was displayed by both males and females, and the majority of aggressive behavior was directed against same-sexed Individuals. The suggestion that females of this species are normally dominant over males (Smith, 1967) was not supported by the results of the present study. Males displayed much higher levels of aggression than did females, and females generally exhibited very low levels of aggression toward males. In addition, high-aggression males more frequently performed a behavior, aggressive digging, that could function to display their aggressive status. Although the frequencies of aggressive behaviors In paired and single groups were very slmi lar, the aggressive index Indicated that individuals In paired and single groups behaved differently. Individuals In single groups did not appear to discriminate between the targets of their aggression as wel I as paired Individuals did. Overal I, the differences In aggressive behavior between paired and single groups may Indicate a tendency for reduced aggression toward opposite-sexed Individuals, especially pair members, In paired Individuals. This Is particularly true of paired males, which displayed both reduced total frequencies of aggression and a lower aggressive Index, against females with which they had been paired than against those with which they had not been paired. Superior aggressive ab! I lty would appear to provide some social benefits for Individuals, as both males and females nested more frequently with high-aggression rather than low-aggression Individuals of the opposite sex. On the other hand faml I larlty, although It

PAGE 70

63 appeared to reduce aggression between pair members, did not have a significant effect on nesting behavior. It would appear from these observations that, In .E..a. pol Ionotus, aggressive abll tty may be a more potent factor in social preference than In famil larlty. However, because It is uni lkely that Individuals under the present conditions were always able to control who nested with them, It Is probably best to use caution In interpreting these results. Aggression and Famll larlty Preference Tests Introduction The results of the semlnatural experiments Indicated that aggression may be an important factor in social preference in .E..a. pol jonotus, but cast some doubt on the Importance of faml I iarlty In the social preference of this species. This experiment was designed to test preference based on aggression and fami I larlty In .E..a. pol Ionotus and .E..a. manfculatus In a more control led manner, through the use of a preference apparatus. Subjects Subjects were Individuals of two species of murold rodents, E.... pol ionotus and .E..a. manfculatus. A total of 40 animals of each species served as subjects for aggressive tests and aggression preference tests. Prior to serving as subjects, animals were maintained as described in the general methods section. Within each species these animals were each assigned to one of 10 groups, with two animals of each sex per group. In addition to the criteria described In the general methods section, no Individual within each group could be

PAGE 71

64 related by more than two common grandparents to any other animal In the group. Fol lowing the aggression tests and aggression preference tests the animals described above also served as "stimulus" animals for familiarity preference tests, while an additional 40 animals, 20 of each sex of each species, served as "choice" animals for these tests. Procedure Procedures were identical tor each experimental group Animals for each group were separated from I itter mates and individually housed in 48 x 27 x 13 cm clear plastic cages. Peromyscus manicu!atus were moved from their colony room to the .E..... pol jonotus colony room. On the fol lowing day, within the first 1/2 of the dark phase of the photoperiod, animals were I ightly anesthetized with ether and marked for identification by shaving them in one of two patterns: either (1) a band was shaved from around the neck area, or (2) a band was shaved from around the middle ot the animals. One animal of each sex was shaved in each pattern. Animals were placed in 48 x 27 x 13 cm plastic cages modified (as previously described under aggression apparatus) tor aggression testing. Al I adaptation and testing were conducted during the dark portion of the photoperiod. Animals were adapted to the preference apparatus on the two days fol lowing the marking procedure. On the first of these two days animals were adapted to the procedure that would be used when they served as "choice" animals. Adaptation to "choice" procedures was as fol lows: the animal was placed in the start box for 5 min, fol lowed by 1 hour free In the

PAGE 72

65 apparatus without other animals present. Animals that did not exit the start box within 1 1/2 min after the door was I lfted were gently prodded with the eraser end of a pencil, often simply lifting the I Id of the start box sl lghtly provided sufficient stimulus for the animal to leave the box. The same procedure was fol lowed during tests. The day fol lowing adaptation to choice procedures, animals were adapted to "stimulus" conditions. Adaptation for stimulus animals consisted of being placed In the stimulus boxes at either end of the preference apparatus for 1 hour. Animals which were tested together as stimulus animals for experimental tests were also adapted together. During adaptation of stimulus animals for the aggression preference tests an opposite-sexed "pretest" animal was al lowed free In the apparatus and its visits to either chamber recorded. This period was designated as the pretest period. Each pretest choice animal had been adapted to the apparatus previously, and served in several pretests with animals of the opposite sex. Fol lowing adaptation to the preference apparatus animals were adapted to the "aggression apparatus" for 2 hours on each of the next three consecutive days. For these adaptation periods the animals home cage was connected to the aggression arena by means of lengths of Tygon tubing inserted into the holes cut in the sides of the home cage and Into the sides of the aggression arena. Animals were restricted to the arena for the first 40 min of the 2 hr period by means of #6 black rubber stoppers Inserted In the ends of the connecting tubes. The stoppers were removed for the remainder of the period so that the animal had access to both the arena and its home cage.

PAGE 73

66 Aggression tests were conducted on 3 consecutive days fol lowing adaptation to the aggression apparatus. Males and females were observed. Tests were conducted by placing the two shaved animals of the same sex Into the aggression arena and observing them for 40 min. Behavior during this period was categorized as approach, displacement, aggressive, or submissive. Frequency of al I aggressive behaviors (total of al I attacks, chases, and fights) was Included under one category because aggressive behaviors other than attacks were extremely infrequent. Aggressive preference tests were conducted on the 2 days fol lowing aggression tests. Two animals of one sex, that had been tested together In the aggression tests, each served once as choice animals. The two animals of the opposite sex, that had been tested together on the aggression test, served as stimulus animals for both tests. Tests were arranged by placing one of the same-sexed pair of stimulus animals In each of the boxes at the ends of the preference apparatus 15 min prior to the beginning of the test, and the choice animal In the start box 10 min later. Tests were Initiated by raising the door to the start box, and thereby al lowing the choice animal access to the apparatus. Test duration was 1 hr, timed from when the choice animal exited the start box. Order of testing was counterbalanced for sexes across days. Although the stage of estrus was not control led for In these tests, smears were taken for each female after she had served as a stimulus animal and on the fol lowing day. On the day after the conclusion of aggression tests for a group, the members of the group were each housed In a 29 x 19 x 13 cm plastic

PAGE 74

67 cage with an lndlvldual of the opposite sex. These "new'' opposite sexed Individuals had been adapted on the previous day to the apparatus under the procedures described for choice animals. These animals each served once as choice animals In the famll iarlty preference tests that fol lowed. Animals that had been paired for the aggression preference tests also served together as stimulus animals for the faml I larlty preference tests (The two same-sexed stimulus animals for each of these tests were two Individuals that had been partners In tests for aggression). This arrangement produced four tests for each group, two tests for each same-sexed set of stimulus animals. Smears were obtained from the females of each group prior to the onset of the dark period on the seventh day after animals had been paired. Tests were conducted with stimulus females only when both of these females exhibited smears consisting of at least 75% leucocytes. This type of smear would normally Indicate a nonreceptlve state. Females that displayed sperm on the smear were tested after they displayed this type of smear. Choice females were tested Individually If they dlsplayed smears with at least 75% leucocytes. Test procedures for choice and stimulus anlmals were as described previously. Results Aggression Tests. The level of aggression (attacks, chases, fights, and rough-and-tumble fights) displayed In the aggression tests were very low. No aggressive behaviors were displayed In four of the ten groups by females of either species. Peromyscus pol ionotus males did not display aggression In two groups, while .E...._ manfculatus males did not display aggression In three groups. The comparison of total

PAGE 75

------68 values (for all three tests) for the four behavioral categories recorded are displayed by sex for each species in Table 13. Only the comparison of .E..... pol lonotus males and females on frequency of aggressive behavior was significant, with males displaying a higher frequency of aggressive behaviors. Because the frequency of aggression In these tests was very low It was difficult to determine which an i mal of a pair was actually the "most aggressive". Instead, the total frequency of approaches and aggressive behaviors was used to provide an indication of which animal of a pair might be more aggressive. This total frequency score, although not an aggression score per se, does al low a comparison of the tendency to Initiate Interactions or "assertiveness" of the two Individuals In a pair. It would seem reasonable to expect that the less timid of two Individuals under these test cond i tions might also be more I lkely to exhibit more aggression under other conditions. The Individual of a pair of animals In aggression tests that displayed the greatest tendency to Initiate Interactions wll I be termed the "high-Interaction" individual, while the Individual that displayed the lower tendency to Interact wll I be termed the "low-Interaction" Individual. Aggression Preference. Table 14 presents data on the preferences of animals of each sex for high or low-Interaction Individuals of the opposite-sex. No preference for high-Interaction animals of the opposite sex was displayed by~ pol ionotus of either sex. Peromyscus manlculatus males, however, did display significantly longer durations of visits with high-Interaction females than low-Interaction females

PAGE 76

Measure Approach A gg re s s i on Di s place m ent S u bmission 1-test -'1f_c38 Table 13 Comparison of Mean Total Frequency of Behaviors in Aggression Tests by Sex for Each Species P. po I I onotus P. manlculatus Ma l e Female Male Mean CSE) Mean (SE) t Mean CSE) Mean 68.85 12 74 49 45 5.84 1.38 34.90 7.29 27.60 3.30 1.35 2 0 .12 2 29* 1. 75 75 1.45 5.45 2.80 1.15 53 1.51 1.85 76 1.15 4.10 2.21 .25 .14 1. 74 .05 .05 .05 2-tal I *ll<.05 F e male O'I (SEl t \.0 6.18 .76 .58 .32 6 9 .68 .05 o o

PAGE 77

Table 14 Preference by Males and Females for High-Interaction and Low-Interaction Animals of the O ~~ osite Sex Male Female Measure E.. po I I onotus No. ot visits Total duration of visits Mean duration of visits E.. man!cu!atus No. of visits Total duration of visits Mean duration of visits Al I durations ere In seconds. Palred-i I-tall .l1f=l9 High Interaction Mean (SE) 86.9.5 14.01 616.00 123.49 10.87 2.70 8.5.40 56.43 1220.50 248.61 66.59 29.19 *J).<,05 Low Interaction Mean (SE) 96.65 16.52 464 .65 109.94 7 .39 1.85 25.50 4.08 548.50 163.27 27 .75 9.83 High Low Interaction Interaction t Mean (SE> Mean (SE) .56 54.95 6.54 54.15 7.38 1.04 987 .10 202.47 769.30 1.50.96 1.39 28.66 7.78 19. 74 5.43 1.06 55.75 18.59 59.80 25.40 1,93* 1031.90 275.59 595.43 202.89 1.19 44.22 14.31 21.81 9.41 t ""'-I 0 .14 .76 .95 .41 1.07 1.18

PAGE 78

71 and 16 of 20 males visited high-interaction more frequently than low-Interaction females (sign test, N=20, ~=4, ~<.01). High-interaction f_. maniculatus females and low-Interaction .E.... manjculatus males both displayed significantly longer durations of visits with high rather than low-interaction animals of the opposite sex (means for high-interaction females with high and low-Interaction animals= 1155 sec and 159 sec, one-ta! I palred-1: .d.f.=8, 1=2.37, means for low-interaction males with high-Interaction and low-interaction animals= 1559 sec and 468 sec, one-ta! I palred-1: .d.f.=9, 1=2.13; ~<.05 for both comparisons). Although the stage of estrus for females in aggression tests was not control led, data were aval I able for this factor. Comparisons of male preference for high-Interaction and tow-Interaction females were made for these tests in which both stimulus Individuals were In dlestrus (see Table 15). The only significant finding was a preference by .E.i. manJculatus males for high-interaction females by the measure of duration of visits. This is also the only comparison which had been significant when data from al I females was included. Comparisons could not be performed within the non-dlestrous condition as there were no cases for .E..... pol jonotus in which both stimulus females were non-dletrous, and only two such cases for .E.... manjcufatus females. Comparisons of male preference for dlestrous versus non-dlestrous high-Interaction females and diestrous versus non-dlestrous low interaction females are presented In Table 16. Peromyscus pollonotus males displayed more visits to non-dlestrous high-interaction females than to diestrous high-interaction females, and .E.... manJcu!atus males

PAGE 79

72 Table 15 Comparison of Male Preference for High-Interaction and Low-Interaction Females In Dlestrus High Low Interaction Interaction Measure Mean CSE) Mean CSE) .E.... po I lonotus No. of visits 70.86 11 41 76.00 16. 18 Total duration of visits 618.14 152 .07 419.60 115.14 Mean duration of visits 11 .22 2. 75 8.47 2.54 .E... manjcufatus No. of visits 217.00 187.73 17.50 3.85 Total duration of visits 1291.28 510.14 11 4. 94 61 .94 Mean duration of visits 71 .55 48.03 6.32 2 36 Al I durations are In seconds. Palred-1 .E.... pol jonotus Q.f.=13 .E... manJcufatus .d.f=5 1-tal I *~<.05 t .29 1.33 1. 12 1.07 2.43* 1.37

PAGE 80

Measure No. of visits to high No. of visits to low Total duration of visits to high Total duration of visits to low Mean duration of visits to high Mean duration of visits to low All durations ere In seconds. 1-test .!:..,_ pol lonotus .ll..f.=18 Table 16 Preference for P. polionotus and P. maniculatus Ma 1 es for Hi gh-Tnteracti on and Low-Interaction Females in Diestrous or Non-Diestrous Condition P .e_ol lonotus P. manlculatus Dlestrvs Non-DI estrus DI estrus Non-DI estrus Meen (N) SE Mean (N) SE t Mean (N) SE Mean (N) SE 73.31 ( 16) 11.16 141 .so (4) 49.83 2.12* 145.30 (10) 112.74 27.75 (8) 7.19 93.56 ( 18) 16.10 124.50 (2) 106.50 .55 16.58 I 12) 2.63 30.67 (6) 1.78 670.75 (16) 148.30 397 .oo (4) 151.95 .88 1353.17 ( 10) 332.96 1355.66 (8) 428.60 490.72 (18) 120.54 230 .oo (2) 110.67 ,70 532.03 C 12) 234.06 459.89 (6) 192.04 12 72 ( 16) 3.20 3.46 (4) 1.85 1.41 57.57 ( 10) 28.54 94.38 (8) 64. 74 7.76 ( 18) 2.03 4.05 (2) 2.58 .59 34.61 ( 12) 15.73 15.43 (6) 7.01 manlculatus .ll..f.=16 2-tel I *si< .05 ***si< .005 t --.J w .93 3.55** 11 .00 .20 .56 .83

PAGE 81

Table 17 Preference for High and Low Interaction Males by Diestrous or Non-Diestrous P. polionotus and P. maniculatus Females P, .e_ol lonotus P. manlculetus DI estrus Non-0 I estrus 0 I estru_s __ Non-DI estrus Measure Mean (N) SE Mean (N) SE t Mean (N) SE I-lean IN) SE No. of visits to high 58.21 (14) 8.02 47.:n (6) 11.62 ,75 42.18 (11) 13.00 82.57 (7) 49.68 Ile. of visits to low 54 .14 (I 4) 9.28 54.17 (6) 12.96 .oo 40,36 ( 11 l 15.33 97 .86 (7) 69.58 Total duration of visits to high 920.19 (14) 224.78 1143.22 (6) 453.60 .49 1344.79 (II> 410.50 779.43 (7) 418.81 Total duration of visits to low 872.55 (t 4) 211 .CJ2 528.39 (6) 44.00 1.05 624.82 ( 11) 288.52 297 .95 (7) 97.68 Mean duration of visits to high 24.:50 (14) 8. 19 38.82 (6) 18. 16 ,85 55,86 ( 11) 18.66 :56.92 ( 7) 28.73 ~ean duration of visits to low 22.10 (t 4) 7.52 14.2} (6) 4.76 ,65 21 .04 ( 11) 12.:n B.51 (7) 2.72 All durations ere In seconds. 1-test .E.. po!lonotus .d.1. moolcvratus cttt6 2-tell for el I canperlsons -..J t +:> .96 .99 .92 .87 .58 ,79

PAGE 82

75 visited non-dlestrous low-Interaction females more frequently than di estrous low-Interaction females. Al I other comparisons of male preference based on stage of estrus were non-significant. The stage of estrus did not slgnlflcantly affect female preference for high or low-interaction males of either species (see Table 17). Famll larjty Preference. Male and female. pol lonotus did not display preference for faml I lar Individuals over unfaml I lar Individuals of the opposite sex by any measure, although the comparison of the total duration of visits did approach significance for females (one-tal I palred-1, .d.f=19, 1=1 .47, ,p_=.054). Peromyscus manlculatus males and females displayed significantly more visits to faml I lar than to unfamll lar Individuals of the opposite sex. Females also displayed longer durations of visits to faml I Jar males than to unfami I lar males (see Table 18), and a greater number of females exhibited more visits to famil tar than to unfamll Jar males Cone-tall sign test, N=18, A=5, ,p_<.05). Because stimulus animals In famil larity preference tests had previously been evaluated In aggression tests, the ''attractiveness" of these animals In famll rarity preference tests could also be evaluated on the basis of their tendency to Interact with other animals. These comparisons are presented In Table 19. Peromyscus pol ionotus females displayed significantly more visits to high-Interaction than to low-Interaction males, and the difference In the number of females that spent longer durations with high-Interaction than low-Interaction males was also significant (one-tat I sign test, N=20, x=5, ,p_<.05).

PAGE 83

Table 18 Preference for Familiar and Unfamiliar Animals of the Opposite Sex by Males and Fe m ales of Each Species Male Female Famlllar Unfaml I lar Fam I I lar Unfaml Iler Measure -E.... pol Jonotus No. of v isits Total duration of visits Me an dura t ion of visits f.... man!cu!atus N o of visits Total duration of visits Me an duration of visits Al I durations are In seconds. Polred-1 M 1-tal I Mean 128.00 522.22 5,87 46.75 978.13 37,71 ~<.05 CSE) Mean (SE) 19.65 144 30 22 95 99.31 539.47 105.04 1.37 6.68 1.96 10.22 32.15 4.61 209. 73 781 ,58 215.56 10.13 37.88 13.38 t Mean (SEl Mean (SEl .78 98.15 12.90 91. 70 16.47 .11 773 .62 155.50 428.88 138.04 .38 12.10 3.65 9.63 4.75 1.78* 32.15 6.62 18.10 3.31 .55 1439.80 295 83 540.90 199 16 .01 183 .04 85.88 45.27 27.30 t .48 '-J 1. 47 en .42 2.42* 2.08* 1 .46

PAGE 84

Table 19 Preference by Males and Females for High-Interaction and Low-Interaction Animals of the Opposite Sex in Familiarity Tests Male Female High Low High Low lnter'lctlon Interaction Interaction Interaction Measure E.... pol Jonotus No. of visits Total duration of visits Mean duration of visits E.... man!curotus No. of visits Total duration of visits Mean duration of visits All durations ere In seconds, Palred-1 .d.1 I-tall Mean 136.45 440.75 4,93 40.85 999.02 40.21 *Jt< .05 CSE) Mean (SE) 21.92 135 .85 20.96 54.31 620.93 130.77 .89 7.62 2.19 8.14 38.05 8.06 225.21 760.70 198.13 12.70 35.38 10.95 t Mean (SE) Mean (SE) .03 110 .95 17 .34 81.90 12.94 1.19 676.00 148.56 526.50 153.96 1.29 12.43 4.93 9.29 3.39 .32 26.40 5.79 23.85 5. 13 .67 1032.45 289.93 948.25 253.37 .28 160.82 85.62 67,50 32.58 t 2.19* .61 .53 -...J -...J ,39 .I 8 .96

PAGE 85

78 Discussion Whereas individuals observed In the seminatural apparatus had exhibited appreciable levels of aggressive behavior, levels of aggression displayed by Individuals In the aggression apparatus were very low. This finding was somewhat unexpected. The object of the procedures fol lowed in the present study had been to condition Individuals to treat the aggression arena as an extension of the home cage. In previous observations Individuals housed In cages Identical to those used to form the aggression arena had displayed fairly high levels of aggression to Intruders after one to two weeks of residency (unpublished observations). In the present study Individuals were tested for aggresslvlty In the arena on the seventh through ninth days of residency in the home cage. Although individuals did not have access to the home cage during aggression tests, they had been al lowed to travel freely between the home cage and aggression arena during adaptation. In addition, during aggression tests the home cages and the aggression arena were attached in a manner that al lowed a fairly free flow of air between them. Many Individuals were observed to spend long periods sniffing and gnawing at the entrances to their home cages. Individuals therefore appeared to recognize their home cage as opposed to a strange cage (unfortunately these observations were not quantified). During aggression testing, however, lndivlduals did not behave as residents In the aggression arena, nor did they defend the entrances to their home cage. Animals in these tests were simultaneously exposed to olfactory cues from both their home cage and that of their opponent. These test conditions may have led to

PAGE 86

79 cont I lctlng "f lght" and "f I lght" responses (See Hinde, 1966), and thereby resulted In low aggression scores. It Is of Interest that Individuals In the seminatural apparatus displayed high levels of aggression toward one another Tmmediately upon being al lowed access to the central arena, even though none of these Individuals had previous exposure to this area, and had been In residence in the connected home areas only three days. The observation of higher levels of aggression under the seminatural conditions than under aggression-test conditions may be due In part to the fact that Individuals In the seminatural apparatus were exposed to opposite-sexed Individuals duri n g tests while individuals In the aggression apparatus were not (Barnett, Evans & Stoddart, 1968; Brain, Benton, & Bolton, 1978; deCantazaro, 1981; Flannel ly & Lore, 1977; O'Donnel I, Blanchard, & Blanchard, 1981). Exposure to females has been demonstrated to increase male-male aggression In .E.... manlculatus baJrdJ (Terman, 1982; Dewsbury, Personal communication). Exposure to opposite-sexed lndivlduals was, however, not required to elicit aggression In the previously mentioned tests of resident .E.... pol Jonotus In aggression-arena-sized cages; and males In the semlnatural single-housed condition were observed in several tests to Initiate high levels of attacks and chases prior to exposure to females. Preferences for high-Interaction (and presumably more aggressive) Individuals were not as strong as might have been predicted from the results of the semlnatural experiments In the present study, or from the results of previous studies (e.g., Blalr & Howard, 1944; Eisenburg, 1962). Although in the majority of comparisons (over 80%)

PAGE 87

80 scores on the measures of preference for high-Interaction individuals were higher than those for low-interaction individuals, most of the differences displayed between high and low-Interaction Individuals were non-significant. This may be a reflection of the low levels of aggression displayed In these tests. Previous Investigators (e.g. Huck et al., 1981) have hypothesized that the differences In odors displayed by dominant and subordinate animals are mediated by differences in the physiological changes Induced In these Individuals through aggressive encounters. The levels of aggression in the present tests may not have been high enough to fully Induce the physiological changes necessary for clear-cut discriminations on the part of choice animals. Although levels of aggression were low in aggression tests, females of both species, and .E.... maniculatus males, displayed significant preferences for the more "assertive'' individual of the opposite sex under some preference test conditions. Significant preferences were not displayed for low-Interaction individuals of either sex In either species. Under the assumption that Individuals that are more assertive would also normally be more aggressive, these findings are consistent with the hypothesis proposed earl !er that Individuals of these species should prefer aggressive opposite-sexed Individuals, and also with the nesting behavior exhibited by .E... pol Ionotus In the semi natural apparatus. In famll iarity preference tests .E.... manlcuiatus of both sexes displayed preference for f a mll lar Individuals of the opposite sex, while .E.... pol jonotus did not display such preference. Although the

PAGE 88

81 lack of preference displayed by E. pol fonotus In the faml I larlty preference tests ls consistent with observations made In the semlnatural study, results of the famll larlty preference tests are contrary to predictions made earl fer as to the behavior of these two species. SJbl Ing Preference Tests Introduction Individuals of most rodent species wl I I be exposed to slbl lngs during development. Such exposure may, of Itself or In conjunction with genetic factors, Influence mate selection (Grau, 1982; Halpin & Hoffman, 1982; Smith, 1966). The general consensus holds that, except under special circumstances, Individuals should prefer to breed with non-relatives (Daly & WIison, 1978; Dewsbury, 1982a; Krebs & Davies, 1981; Wlttenberger, 1981). Rasmussen (1970), however, has suggested that Inbreeding may be fairly extensive In some species of Peromyscus, particularly E..... manlculatus (Rasmussen, 1964); and Howard (1949) has proposed that Inbreeding may account for as much as 10 percent of breeding in .P..... manlculatus. Smith (1966) has suggested that "a considerable amount of Inbreeding" (p. 50) also occurs In E..... pol lonotus. Not al I Investigators agree with these proposals however. Selander (1970) has questioned the genetic basis for Rasmussen's (1964) conclusions regarding .E.... manlculatus, and other Investigators (Dewsbury, 1982a; Hi I I, 1974) have demonstrated suppressed reproduction for slbl Ing matings In this species. Foltz (1981b) has also questioned Smith's (1966) proposal of high levels of Inbreeding In

PAGE 89

82 .e.._ pol ionotus. The present study was designed to evaluate preference for sibl lngs In E... pol Jonotus .and. .E..t. maniculatus. Subjects Both E... polionotus and .E..t. maniculatus served as subjects for slbl Ing preference tests. Subjects were selected from 12 I ltters of each species that contained at least two animals of each sex. Two animals of each sex were selected from these I ltters, under criteria In the general methods section, and maintained together throughout the experimental procedure. Litters selected for groups were unrelated by more than one common grandparent. Two I ltters of each species comprised an experimental group. Procedure Individuals were ear-punched for identification, and E... maniculatus I ltters were moved to the E... pol ionotus colony room. On the fol lowing day animals were adapted to the preference apparatus, without other Individuals present, as both stimulus animals and choice animals. Preference tests were of two types, same-sex tests and opposite sex tests. In same-sex tests choice animals had a choice between a same-sexed slbl Ing stimulus animal and a same-sexed nonslbl Ing. In opposite-sex tests animals had a choice between two opposite-sexed lndlvlduals, one a slbl Ing and one a nonslbl Ing. Each animal In a group served twice as a stimulus animal and once as a choice animal for each type of test. In an opposite-sex test, for example, males 2 and 4 would serve as stimulus animals for choice females 2 (one of the 2 male siblings) and 4 Ca 4 male slbl Ing). They would each also serve as

PAGE 90

83 choice animals with stimulus females 1 (a 2 male slbl Ing) and 3 (a 4 ma I e s I b I I ng) Preference tests were conducted on the two days fol lowing adaptation. Al I tests of one type (i.e. opposite-sex tests) and half of the tests of the other type were conducted on the same day. Testing was completed on the second day. The order of test type across days was counterbalanced. The number and duration of visits to each chamber were recorded on each test and for the adaptation period. Vaginal smears were obtained for each female before the beginning of the dark cycle on each test day. Results Peromyscus pol ionotus females demonstrated a preference for siblings over nonslbl lngs (see Table 20). Sibl Ing males were visited significantly more frequently than nonslbl Ing males, and a significantly larger number of females spent longer durations with slbl Ing rather than nonsibl Ing males (sign test, N=24, ~=6, 2-tail ~<.05). They also spen+ significantly longer durations with slbl Ing rather than nonslbl ing females. None of the comparisons for slbl lngs versus nonsibl lngs were significant for E..... pol lonotus males or for E..... manJculatus of either sex (see Tables 20 and 21). It ls, however, of Interest that scores for E..... polionotus males on tests with opposite sexed animals mirror those of E..... pol jonotus females (higher scores for slbl lngs), while for al I but one measure (average duration of visits for females) E.... manlculatus display higher scores for opposite-sexed nons i b I I ngs.

PAGE 91

Table 20 Preference by~polionotus Males and Fem a les for Siblings and Nonsiblings of the S a me-Se x and Opposite-Se x Total (Male and Female) Males Females Slbl ln_g_ Nonslbl Ing Slbl Ing Nonslbl Ing Slbl Ing Nonslbl Ing Measure Mean CSE) Mean (SE) t Mean CSE) Mean CSE) t Mean (SE) Mean CSE) Pr e ference fQ.c Q pl)Q Sl!e-Seis No. of visits 109.83 13.45 91.65 11 .83 1.93 111.42 16.48 107.67 17.66 .35 106,25 21.61 75.62 15.43 Total duration of visits 840.42 113 .62 592.93 94.51 1.64 701 .33 124.02 690.96 145 .59 .06 979.50 188.94 494.90 120.30 M e an durati o n of visits 22.28 4.85 17.30 4.59 1.32 22.40 7.71 22.25 8.38 .03 22.16 6 05 12 34 3 68 Preference fQ.c S ame -S ex No. of visits 134.92 20.69 100.48 15.21 2.01 153.71 29.10 102.46 14.80 1.97 116.13 29.54 98 50 26.95 Total duration of visits 740.85 107.23 516.38 89.11 1.57 622 13 131.40 614.35 164.46 .04 859.58 168.29 418.42 67.62 M ean duration of visits 18.20 4.72 28.12 14.07 .69 17 .59 7.82 46.87 27.75 1.05 18.82 5.47 9.37 2.82 Al I durations are In seconds. Palr e d-i Total .a.f=47 Male end Female .a.fz23 2-tal I *fl<.05 co t .t,, 2.16* 2.00 1.61 .79 2.45* 2.04

PAGE 92

Measure Preference fQr. Opposite-Sex Table 21 Preference by P. maniculatus Males and Females for Siblings and NonsTblings of the Same-Sex and Opposite-Sex Totet (Mates end Females) Males Females Sib 11 ng No,, s I b I I n9_ Slbl Ing Nonslbl Ing Slbl Ing Nonslbl Ing Mean (SE) Mean (SE) t Mean (SE) Mean (SE) t Mean (SE) Mean (SE> t No. of visits 16.17 Total duration of visits 837.83 Mean duration of visits 127.46 2.13 20.81 3.59 1.40 17.17 3.14 17.88 2.37 .34 15.67 2.94 23.75 6.81 1.37 166.46 1412.64 186.58 1.84 885.76 231 .94 1542.86 260,28 1.49 789.89 243.40 1282.42 270.29 1.09 69.27 159.99 43.89 .38 65.42 22.13 157.58 50.86 1.53 189.51 137.06 162.41 72.71 .17 Preference t2C Sarne-sex No. of visits Total duration of visits Mean duration of visits 18.73 2.27 17.40 2.09 .69 18.58 3.24 17.58 2.58 .41 18.88 3.24 17.20 3.35 .54 1144.24 166.51 1108.87 178.61 .11 1134.33 246.92 1250.43 250.54 .26 1154.15 228.76 967.31 256.64 .43 118.33 34.31 182.54 73.67 .75 124.63 51.15 112.04 33.03 .19 112.03 46.83 253.03 143.72 .38 Al I durations ere In seconds. Palred-1 Total Jti;47 Mele end Female J1.t~23 2-tel I ~>.05 tor al I comparisons co (Jl

PAGE 93

86 Table 22 Comparison of Male Preference for Sib I Ing and Nonslbl ing Females in Di estrus Sib 11 ng Nons I b 11 ng Measure Mean ( SE) Mean ( SE) t E... po I l onotus No. of visits 90.83 24.40 95.33 21 10 .33 Total duration of visits 777.06 173.36 904.81 259.62 .41 Mean duration of visits 28.66 13. 16 35. 11 15. 51 .94 E... manicu!atus No. of visits 18.21 4.45 14.64 3.22 1.36 Total duration of visits 1048.67 323. 90 1448.26 367.33 .64 Mean duration of visits 87.96 35. 79 201 .42 84.01 1.12 Al I durations are in seconds .t-test po I I onotu s .M= 11 ..E...... manicu!atus .M=14 2-tal I ~>.05 for al I comparisons

PAGE 94

Table 23 Preference by P. polionotus and P. maniculatus Males for Sibling and Nonsibling-Females in Diestrous and Non-Diestrous Conditions P. pol lonotus P. manlculatus DI e strus Non-0 I estrus DI estrus Non-DI estrus M e asure Mean CN) SE Mean (Nl SE t Mean (Nl SE M e an CN) SE t No. of visits to slbl lngs 98.06 18 18 04 151 .50 6 35.39 1.44 18.78 18 3.80 12.33 6 12 79 .89 N o. of visits to nonsl b l lngs 110 61 18 19.90 98.83 6 41.02 .28 16.44 18 2.77 22.17 6 4.53 1.05 Total du r ation of v isits to siblings 731.83 18 141 .89 609,83 6 274.62 42 978.48 18 271 .95 607.61 6 463 55 ,68 Total duration of visits to nonslbllngs 727.02 18 184.01 582.78 6 203.69 .42 1432,89 18 304.40 1872.78 6 521.85 .72 Mean duration of visits to slbllngs 25.08 18 9.52 14.34 6 12.31 1. 79 75.07 18 28,49 36 48 6 22 58 75 Mean duration of visits to nonslbl lngs 25.00 18 10.80 14.01 6 9.28 .56 169.53 18 66.48 121 71 6 46.62 .40 Al I durations are In seconds. 1-test Jti.=22 2-tal I ~>.05 for all comparisons 00 '-I

PAGE 95

Table 24 Preference for Sibling and Nonsibling by Diestrous and Non-Diestrous P. polionotus and P. maniculatus Females P. pol lonotus P. manlculetus DI estrus Non-DI estrus DI estrus Non-DI estrus Measure Mean (N) SE Mean (Nl SE t Mean (N) SE Mean (N) SE t No. of visits to slbl lngs 116,95 ( 19) 26.59 75.20 (5) 21.26 .78 14.56 < 18) 2.50 17.00 (6) 9.74 .35 No. of visits to nonslbl lngs 75.94 (19) 18.96 74.40 (5) 20.57 .04 26.56 ( 18) 8.65 15.33 (6) 8.46 .71 Total duration of visits to siblings 1048.26 (19) 219.76 718.20 (5) 371.22 .70 850. 70 C 18) 293.33 607 .44 (6) 451.16 ,42 co Total duration of visits to nonslbl lngs 554.00 (19) 147 .42 270.33 (5) 108.88 .96 956.07 C 18) 274.65 2261.44 (6) 564.97 2.27* co Mean duration of visits to slbl lngs 21 .94 ( 19) 6.50 23.00 (5) 16.97 .07 229.13 ( 18) 181 .91 70.63 (6) 65.91 .49 Mean duration of visits to nonslbl lngs 13 .55 ( 19) 4.43 7. 77 (5) 5.65 .63 57 .38 ( 18) 23.00 477.47 (6) 255.73 2 .87** Al I durations ere In seconds, 1-test .!1.1=22 2-tall *~<.05 **~<.01

PAGE 96

Table 25 Preference for Sibling and Nonsibling Females by Diestrous and Non-Diestrous P. polionotus and P. maniculatus Females P. eol lonotus P, manlculatus Dlest r us Non-DI estrus DI estrus Non-DI estrus Measure Mean (N) SE Mean (N) SE t Mean (N) SE Mean (N) SE No. of visits to slbl lngs 126.37 ( 19) 36 57 77.20 (5) 27.08 .67 15.18 ( 17) 3.18 23 80 (5) 9.28 No. of visits to nonslbl lngs 105.16 ( 19) 33.63 73.20 (5) 22.66 .47 13.06 ( 17) 2.27 18.00 (5) 7 .13 Total duration of visits to slbllngs 909.35 ( 19) 203.09 670.47 (5) 255.13 .57 940.14 (17) 262 81 1576.80 (5) 598.22 Total duration of visits to nonslbl lngs 434 53 ( 19) 81 .01 357 .20 (5) 113.08 .46 1083. 75 ( 17) 317.14 887 .53 (5) 611.42 Mean duration of visits to slbl lngs 21 .55 ( 19) 6.77 8 42 (5) 2.34 .97 123.60 ( 17) 64 70 96,24 (5) 55.35 Mean duration of visits to nonslbl lngs 10.54 (19) 3.53 4 93 (5) .74 80 306.08 ( 17) 198.16 172.44 (5) 160.74 Al I durations are In seconds. 1-test _p_ol lonotus i1.f=22 ..f., men I cu I etus Jll."20 2-tel I ~>.05 for ell comperlsons t 1.13 .86 1.10 (X) I..C .29 ,22 .35

PAGE 97

' 90 As with the aggression preference tests comparisons were made of male preference for slbl lngs and nonslbl lngs in dlestrus and of male preference for di estrous versus non-dlestrous slbl lngs and nonslbl ings. None of these comparisons were significant for either .E... pol lonotus or .E.._ manlculatus males (see Tables 22 and 23). Comparisons of the preferences of females In different stages of estrus did, however, yield some significant differences. Although .E.... pol lonotus females exhibited no significant differences In preferences based on stage of estrus, .E.... maniculatus females did display significantly greater preference for nonslbl Ing males, by the measures of total and average durations of visits, when in a non-diestrous condition over a diestrous condition (see Tables 24 and 25). The possibil lty of I ltter effects on preference scores was also evaluated by conducting a one-way analysis of variance on the "difference scores" between preference scores for sibl lngs and nonslbl lngs. Significant I ltter effects were found for the average duration of visits by .E.... pol lonotus males to females (F(ll,12)=3.77, ~<.05). and for the total duration of visits by .E..._ pol lonotus females to males (F(ll,12)=3.08, ~<.05). Discussion While Peromyscus polionotus males generally displayed higher scores on preference measures for slbl lngs than for nonslbl lngs, these comparisons were not significant .E.._ pol lonotus females, however, did display significant preferences for slbl ings over nonslbl lngs. The results of this study, therefore, may offer some support for proposals of high levels of Inbreeding In E.... pol ionotus (Smith, 1966). The

PAGE 98

91 observation that scores for preference by .E...... manlculatus males and females were generally In the opposite direction from those for .E...... pol ionotus Is of Interest. This difference may Indicate a greater preference for slbl lngs by .E...... pol lonotus than by _f. maniculatus. It is also of interest that non-dlestrous .E...... manlculatus females di splayed a greater preference than diestrous females for nonslbl Ing males, since females In a non-dlestrous condition would be more I lkely to be receptive. These results are consistent with previous studies demonstrating suppression of reproduction In slbl Ing matings of .E..... manlculatus (Dewsbury, 1982a; HII I, 1974), and the lmpl felt concluslon from these studies that Inbreeding should be avoided by members of this species.

PAGE 99

SECTION IV GENERAL DI Sa.JSS I ON In the general discussion the observations of the present study are examined in I ight of previous research, and interpretations are suggested for these observations that are consistent with the ecology and mating systems of .E.... manjculatus and .E.... pol ionotus. The general discussion section is divided into six subsections. The first of these subsections examines aggressive ability as a factor in preference. This subsection begins with a fairly extensive overview of the ecology of .E..... maniculatus and .E.... pol ionotus, and also presents evidence for the role of aggression in the ecology of these two species. The ecological information presented in this subsection serves as a background for discussions which fol low in al I subsequent subsections. The discussion of the ecology of these species is fol lowed by a discussion of factors that may provide an adaptive basis for selection of aggressive mates in these species. The second subsection deals with fami I iarity as a factor in preference and with the effect of prior breeding experience on preference for familiar individuals, and includes a discussion of the opportunities that may be avai I able for .E.... manjculatus and .E.... pol jonotus to uti I ize fami I larity as a basis for mate selection. This subsection is fol lowed by a subsection on the related topic of kinship as a factor in preference. The subsection on kinship discusses 92

PAGE 100

93 evidence for and against Inbreeding In .E...... manlculatus and .E..... pol Jonotus, and the ecological and social factors that may affect preference for slbl lngs as mates In these species. This subsection is fol lowed by a subsection on the evolution of monogamy In .E...... pol Ionotus, and the summary for this study. Aggressive Ab! I ity as a Factor In Preference Many of the observations In the present study were consistent with the general hypothesis that aggressive abil tty may be Important In the social behavior and mate selection of monogamous and polygamous species. They were also consistent with the specific predictions that aggression should be an important component of the social behavior of .E..... pol jonotus, and that E_. pol lonotus and .E...... manlculatus of both sexes should prefer mates with high aggressive abl I tty. In the seminatural experiments aggression was routinely displayed by both male and female .E..... pol [onotus, and both males and females of this species nested more frequently with the more aggressive of the two opposite-sexed Individuals. Female .E..... pol [onotus also displayed preference for the more assertive of two males In famll larlty preference tests; and preference for more assertive Individuals was displayed by .E..... maniculatus males and high-Interaction P. manlculatus females In aggression preference tests. The preferences exhibited by these species may be mediated through advantages In reproduction gained by Individuals that choose mates with good aggressive abi I tty over those that choose mates with poor aggressive ab! I lty. Some of the possible advantages accrued by Individuals that choose mates with high aggressive abil lty have been

PAGE 101

--------94 briefly discussed In previous sections. The present discussion will focus on the advantages that might be gained through such choice by lndivlduals of the two species of interest In this study, .E.... pol Jonotus and .E.... manJculatus, In the context of the ecology and mating system of these two species. Ecology, Mating System, and Aggressive Abi I tty Many ecological variables wl I I play a role In determining to what extent aggression may be adaptive for individuals of any particular species, and thus also the Importance of aggressive abi I ity as a qual lty in mates. The ecology of a species may often be as major a fac~or as Its mating system In determining the Importance of aggressive abil lty to reproductive success in that species. Among the more general ecological problems with which lndivlduals of a species must cope with in order to reproduce successfully and one that also affects the mating system of a species, ls the avallabi I lty and defenslbi I lty of resources necessary to reproduction (Brown, J. L., 1975; Clutton-Brock & Harvey, 1978; Emlen & Orlng, 1977; Hal I !day, 1978; Ori ans, 1969). Aggressive abi I lty may play an Important role In the acquisition and defense of these resources In monogamous and non-monogamous species. Individuals that choose mates high In aggressive abi I lty may be Insuring that adequate resources wit I be available for themselves and their offspring; choosing such mates should therefore be more adaptive than choosing mates with low aggressive abil lty.

PAGE 102

95 Peromyscus manlculatus Peromyscus manlculatus occurs In a wide variety of habitats over most of the North American continent (Baker, 1968; Hamilton, 1943; Hooper, 1968). This species wil I accept a wide variety of food items (Cogshal I, 1928; Martel I & Macaulay, 1981; WII I lams 0., 1955) and nest sites (Blair, 1940; Ham! I ton W. J., 1943; Howard, 1949), and the distribution of the various subspecies in the environment may be governed more by different behavioral responses to different habitat types than by any absolute differences In nesting requirements or food preference (Dice, 1922; Harris, 1952; Wecker, 1963). The subspecies of .E... manjcufatus may for the most part be divided Into two general types, those adapted for and occupying openlands such as fields, and those adapted for and occupying woodlands and brushlands (Baker, 1968). Peromyscus maniculatus balrdl, the subspecies observed In the present study, Is generally found In "open fields, sand beaches, and arable land of the prairie states (Ham! I ton W. J., 1943, p. 270). Peromyscus manlculatus bairdl generally I Ive In overlapping home ranges (Blair, 1940). As Is typical of other Peromyscus (Stickel, 1968), each home range contains several nests and refuge holes, and mice may change nests frequently (Blair, 1940; Howard, 1949). In addition to utll lzlng several types of naturally occurring nest sites (Blair, 1940; Howard, 1949) individuals of this subspecies are capable of constructing their own burrows (Houtcooper, 1972). Peromyscus manicufatus bairdl Is therefore more I ikely to be restricted to particular locations within its preferred habitat by considerations such as the aval labi I lty of sufficient food than by avallabi I lty of

PAGE 103

96 nest sites. This Interpretation receives support from observations by Howard (1949) which indicate that Increasing the number of nests available In an area does not increase the number of resident breeding mice In that area; and by observations which Indicate that~ m.... bajrdi cache food for winter use (Ham! lton W. J., 1943; Howard, 1949), and that the aval labi I lty of food may I lmit the number of resident breeding adults In other subspecies of~ manlculatus (Fordham, 1972; Gashwiler, 1979; Taitt, 1981). The habit of caching food and the large winter aggregations observed in this subspecies (Howard, 1949, 1951) are probably adaptations for winter survival. Energy requirements for these mice In the winter months are high (Howard, 1951) and populations In some local !ties may suffer severe winter mortal lty (Blair, 1940; Howard, 1949). These mice do exhibit an abi I lty to become torpid at low temperatures. In severely cold weather, however, Individual mice may not be able to become torpid without freezing. Uti I ization of cached food al lows individuals to maintain high metabol le rates (and therefore a high body temperature), and huddl Ing In winter aggregations both reduces body heat loss and al lows Individuals to become torpid (Howard, 1951). Winter aggregations generally appear to consist of a breeding pair and at least one prevlous I ltter, additional conspeclfic adults of both sexes, and sometimes Individuals of other species (Howard, 1949). Peromyscus manlculatus balrdl have generally not been observed to breed In the winter (Blair, 1940; Howard, 1949), although a few Individuals may sometimes be capable of breeding through the winter In favorable mlcrohabltats (e.g., Cornshocks: Linduska, 1942).

PAGE 104

97 If food aval labi I lty Is the primary factor determining the sultabi I lty of a particular area (within the preferred habitat type) for breeding in .E..... lih. balrdl, one might expect that It would also affect the social organization and mating system of this species. Because .E..... m.... balrdl appears to utll lze a wide variety of different food Items, the Importance of which may vary seasonally (Houtcooper, 1978), it Is I ikely that defense of the food supply per se Is not economically feasible. Peromyscus maniculatus balrdl appear to have opted Instead for a strategy of I lmitlng the number of breeding Individuals In or near their home ranges. This Is accompl !shed In part by adults aggressively limiting juvenl le settlement In their home range (Ayer & Whitsett, 1980; Enders, 1978; Whitsett, Gray, & Bedi2, 1979). In some subspecies of .E..... manlculatus juvenl le settlement appears to be restricted largely as a result of male aggression toward juvenl les (Fairbairn, 1977; Healey, 1967; Metzgar, 1979, 1980; Mihok, 1979; Sadle l r, 1965); while for other subspecies (Including .E..... m.... baJrdJ) female aggression might be as important as or even more Important than, male aggression In I lmltlng juvenile settlement (Ayer & Whitsett, 1980; Enders, 1978; Fordham, 1971; Taitt, 1981; Whitsett et al., 1979). As In other subspecies of E... manlcu!atus (Fairbairn, 1978; Healey, 1967; Llewellyn, 1980), male aggression In E.... ID.a. baJrdl appears to be under hormonal control (Whitsett et al., 1979). The level of aggression In male .E.... m.... baled[ may therefore fol low a seasonal pattern of changes as described for other subspecies of E... manlculatus (Healey, 1967; Llewellyn, 1980; Metzgar, 1979; Sadlelr, 1965).

PAGE 105

98 The general seasonal pattern of changes In the level of aggression for male .E..... manjcu!atus, as described by Healey (1967), consists of a spring increase In male aggression (which is correlated with an increase In testicular size) to a peak through the major breeding season, fol lowed by a drop In the level of aggression to neg I lg!ble levels at the time fal I aggregations occur. This seasonal pattern of changes In the level of male aggression ls reflected in seasonal changes In social organization. At least some subspecies of .E..... manjculatus have been observed to form large non-aggressive non breeding winter aggregations (Dice & Howard, 1951; Howard, 1949, 1951; Metzgar, 1979). Although sufficient cbservations are not avai I able to permit evaluation of the generaf lty of the tendency of .E..... manlcu!atus to form large winter aggregations, most subspecies of .E..... manlcu!atus do appear to exhibit a spring dispersal period prior to the major breeding season. The shift in behavior and social organization that occurs at this time have probably been best described by Healey (1967) for .E..... m.... austerus. According to Healey a greater number of mice survive the winter than are compatible on the breeding territories. Animals which were resident In the overwintering areas, and their offspring, are most I lkely to be dominant in and therefore most I lkely to settle in these areas, while subordinate animals disperse. Establ !shed residents aggressively exclude new settlers, while aggressive Interactions between neighboring residents are reduced. In .E..... m.... austerus mutual avoidance between same-sexed resident adults may lead to mutal ly exclusive home ranges within sexes, but overlapping

PAGE 106

99 home ranges between sexes (Healey, 1967; Sadleir, 1965). Other authors (e.g., Metzgar, 1979), however, have observed a pattern in this subspecies that is exhibited by several other subspecies of .E.... maniculatus including .E.... fil.a. bairdi -same-sexed home ranges may overlap, but appear to overlap much less extensively than home ranges for opposite-sexed Individuals (Blair, 1940, 1942, 1943; Howard, 1949; Morris, 1955). The general pattern observed In these studies consists of large resident-male home ranges that overlap each other sl lghtly, while each also extensively overlaps several smaller resident-female home ranges. In at least some subspecies residents may also tolerate same-sexed non-breeding subordinates within their heme range (Metzgar, 1979, 1980). The breeding system of .E.... maniculatus appears to be somewhat labile. Although males generally appear to form breeding relationships with a few adult females within their home range (Blair, 1958; Howard, 1949; Mihok, 1979; Terman, 1961), adults have been observed In combinations that Included more than one breeding individual of either sex (Blair, 1958; Howard, 1949), and members of this species have also been observed to form long lasting and apparently exclusive breeding pairs under some conditions (Blair, 1958; Howard, 1949). Metzgar (1979) has proposed a general system to explain the labi I ity apparent in Peromyscus breeding systems. In the proposed system, the home ranges of breeding males overlap those of adult females broadly and the two classes occur together far more frequently than by chance alone. Within a sex, breeding adults are evenly dispersed but considerable home range overlap may occur depending on density and home range size. The large home range of a breeding male usually includes al I or parts of several adult female home ranges. Female ranges may be overlapped by ranges of several breeding

PAGE 107

100 males, especially when male-male overlap is extensive. However, even with extensive overlap, each breeding male might spend most of his time with a particular female (Garson, 1975). Furthermore, under some conditions ( low densities and smal I home ranges), this generally loose male-female association might be expressed as enduring male-female pairs. (p. 142) The particular breeding relationships exhibited by a given population of .E..... manjcu!atus may be largely determined by food availabi I ity, as food availability appears to influence population density and home range overlap in this species, and may also result in an alteration in the sex ratio of the breeding population. A more abundant food supply in an area may result in an Increased density of adult mice in that area (Fordham, 1972; Gashwi ler, 1979; Taitt, 1981 ), and a contraction of home range for breeding individuals of both sexes (Taitt, 1981). Although Taitt (1981) noted an increase in the number of both sexes in an area supplied with additional food; Fordham (1972) observed an increase in the number of females and the proportion of females breeding, but no increase in the number of males. A reasonable explanation for this difference was proposed by Taitt (1981) who noted that while she had provided additional food to a winter population, Fordham (1972) had provided additional food during the breeding season. The aggressive resident males in Fordham's study may have prevented recruitment of additional males, but not females. Abundant food in the breeding season may, therefore, result in a female biased breeding population. A skewed sex ratio may In turn have an effect on the breeding associations exhibited by .E..... filL balrdl. Howard (1949) has noted that "in areas where the sex ratio was not equal, as many as three females I ived in the same nest box with one

PAGE 108

101 male, and as many as three males I ived In one nest box with one female" (p. 14). As noted earlier, although .E..... manjculatus do not appear to defend feeding areas per se, resident animals may prevent over-uti I ization of food supplies within their home ranges by aggressively I lmlting the settlement of potential breeders in these areas. The presence of an adequate food supply within a home range may increase the probability of winter survival for residents and their offspring. The observations reviewed in the preceedlng discussions Indicate that the avallabl I ity and distribution of food Items may have major consequences not only on the distribution and survival of these mice, but on the social behavior and breeding relationships exhibited by them as we I I Peromyscus pol ionotus In I ight of several aspects of the ecology of .P... pol jonotus, choosing mates with high aggressive abil lty may be adaptive for members of this species. One e~ological factor of primary importance to this species is the availabi I ity of suitable nest sites. Because they construct their own burrows (Hayne, 1936; Smith, 1966; Smith & Criss, 1967) .E...... pol jonotus are not restricted by the avallabi I lty of naturally occuring nests per se. This species does, however, require a fairly narrow range of soil conditions for nest construction, and In habitat undisturbed by man is probably restricted to areas in early successional stages (Got ley, Gentry, Caldwel I, & Davenport, 1965), and sandy beach areas. According to Smith (1966) abundance of .E...... polionotus "is correlated with soil type, amount of soi I drainage

PAGE 109

102 (Table 2), type and amount of vegetation. Al I of the habitats occupied by this species are characterized by sparse vegetation and relatively well-drained or recently plowed soils (p. 11). Well-drained fine sand soi Is were preferred for burrowing, and mice "never constructed burrows In hard soi Is where digging was difficult, nor in areas where the hardpan was close to the surface of the ground'' (p. 13). Few mice were observed in heavily forested areas, or In areas with dense vegetation (Rand & Host, 1942; Smith, 1966; Personal observations), and the number of mice nesting In a given area appeared to be negatively correlated with the density of vegetation (Rand & Host, 1942; Smith, 1966). Individual mice construct several burrows In close proximity (Rand & Host, 1942; Smith, 1966) within a fairly wel I defined home range (Blair, 1951; Davenport, 1964) and defend these burrows against intruders (Blair, 1951 ). It is I ikely that in addition to defending burrows within their home range, individuals also aggressively exclude other potential settlers from suitable nest areas near their burrows. This suggestion is supported by the observation that often the burrows within a given area .ail appeared to have been constructed by a single Individual, or pair of individuals (Rand & Host, 1942; Smith, 1966), and by observations In the present study that animals attacked and chased one another in al I areas of the semi natural apparatus, and not just in the area that actually contained their burrow. Although .E.... pol jonotus defend burrows within their home range (Blair, 1951), they do not appear to defend their entire home range (Davenport, 1964). The apparent lack of defense of home range by

PAGE 110

103 .E..._ P-OI lonotus may be a reflection of the fact that this species utilizes a wide variety of food items (Gentry & Smith, 1968; Smith, 1966) that are probably not economically defendable. Although multiple burrows may simply serve a survival function as refuges from predators, the maintenance of several burrows Is more I ikely to act in some manner to maximize reproductive success in .E..._ pol fonotus. Blair (1951) and Rand and Host (1942) observed that .E...... pol jonotus change nests frequently; this frequent change of nest site could be a strategy to reduce the level of parasitic Infestation of offspring .E..._ pol lonotus have also been observed to utll ize unoccupied burrows as food caches (Blair, 1951; Rand & Host, 1942; Smith, 1966). Some evidence exists that populations of this species may at times be food I imited (Smith, 1971; Smith & Blessing, 1969); cached food might provide a food reserve that would al low parents and offspring to survive and/or reproduce during such periods. Alternatively cached food could contain nutrients that, although not critical for survival, might be critical for reproduction. Food caches may therefore al low breeding In seasons during which it would not otherwise be adaptive. Evidence supportive of these hypotheses are Smith's (1966) observations that food-deprived Individuals of this species become torpid at very cool temperatures whl le non-food-deprived individuals do not, and observations of Improved reproductive performance in pairs fed acorns (a frequently cached food item) parasitized by beetle larvae. Abundant cached food may al low Individuals to maintain a level of activity compatible with breeding, even In cooler temperatures, and high-qual lty food caches (e. g.

PAGE 111

104 acorns containing beetle larvae) may provide nutrients that would otherwise not be available in winter months. An additional benefit that may derive from the maintenance of multiple burrows has been discussed by Foltz (1979). Upon the birth of a new I itter older offspring may move into a nearby burrow with their father. The behavior of moving to nearby burrows may al low offspring to extend the period during which they may take advantage of parental resources and care. Offspring that receive extended care may be better able to compete for food and to establish burrows when they disperse than offspring that do not receive such care. This may be of particular importance in .E... pol jonotus because dispersing individuals appear to suffer very hi g h morta1 lty (Smith, 1966, 1968). The maintenance of multiple burrows by .E... pol lonotus appears, as a result of the factors discussed, to be a highly adaptive strategy for members of this species. The facts that E..,_ pol ionotus are restricted to very specific types of habitat, and that individual mice maintain several burrows in an area, probably act as major factors that I lmit the size of the breeding populations in this species. If nest sites are a I imited and critical resource for .E.... pol ionotus, one would expect individuals of this species to compete for them, and to defend them from conspeclfics. According to consensus polygyny should be generally be advantageous to males (Brown J. L., 1975; Daly & Wilson, 1978; Dawkins, 1976; Ori ans, 1969; Verner, 1964), and males should therefore attempt to control I imited resources In a manner that allows them to acquire additional mates. Because nest sites appear to be a

PAGE 112

105 I imited and defendable resource for .E..a. pol ionotus, males of this species might be capable of gaining multiple mates by control I Ing areas suitable for nesting (see Verner & WII Ison, 1966, p. 145). This species has, however, consistently been found to exhibit a monogamous mating system (Blair, 1951; Foltz, 1979, 1981; Rand & Host, 1942; Smith, 1966). According to Emlen and Oring (1977) the two preconditions for a species to exhibit a polygamous mating system are that (1) Individuals must be potentially capable of economically defending multiple mates, or resources critical to gaining multiple mates, and (2) individuals must be able to uti I ize that potential. Several factors may prevent .E.... pol!onotus males from fulfi I I ing these two preconditions for polygamy. Among the more Important of these factors are the distribution of nest sites and food Items, and It Is I lkely that monogamy in .E.... pol jonotus rests upon considerations related to both of these factors. Availability of nes..:ts..... As discL1,5sed previously the number of suitable nest sites for .E..a. pol lonotus in any given area may be very I i mi ted. It is poss i b I e that nest sites for this species may be so I imited as to impose monogamy because two adults are required for their defense (See Wilson, 1975, p. 330). Alternatively a male may be capable of defending a sufficient number of burrows to maintain a single female and her I itter, but nest sites may be too dispersed for a male to defend a sufficient number of burrows to maintain two females. Although the maintenance of multiple burrows appears to be important in terms of the ecology of .E.... pol lonotus, in I ight of the available data

PAGE 113

106 it is difficult to evaluate how many burrows a pair might actually require to maximize its reproductive success. While the avai labi I ity or distribution of nest sites alone might explain monogamy in .E..... pol jonotus, it is most I ikely to be of importance in conjunction with other factors. One might expect for example that if food Items were abundant year-round, burrows would not be used as food caches, and males might be more capable of acquiring additional females. Avaj labj I ity of food items, If suitable habitat for burrowing was abundant a male might be capable of defending enough burrows to maintain several females. However, even if burrows were abundant, females themselves may be too widely dispersed to defend if food items are sparse (Glutton-Brock & Harvey, 1977, 1978; Eisenberg, 1977), or if food items are so widely dispersed around nest areas as to make It highly uni ikely that a female could raise a I ltter without assistance. Under these conditions females may require males to display some evidence of commitment (Maynard Smith, 1977) prior to mating with them, or may Impose monogamy 0n males by aggressively preventing other females access to their mate (Wittenberger, 1979, 1981; Wittenberger & TI I son, 1 980) Aggression and Mate Selection lotraspecific aggression Peromyscus manjculatus, As discussed in preceedlng sections aggression is an important component of the social behavior of Peromyscus maniculatus, and an individual's aggressive ability probably plays a major role in determining if that individual wi I I be capable of establishing and maintaining itself as a breeding member of the

PAGE 114

107 population. In laboratory studies dominant males of this species have been found to be more successful than subordinate males in nesting with females (Blair & Howard, 1944; Eisenberg, 1962), copulating with females
PAGE 115

108 abll ity may be Important in the social behavior and mate preferences exhibited by this species. In the seminatural experiments lndlvlduals of both sexes displayed aggressive behavior, the majority of which was directed against same-sexed individuals. This is consistent with the type of behavior Kielman (1977) has proposed as indicative of monogamy. In addition members of both sexes nested more frequently with the more aggressive of two opposite-sexed individuals, and members of both sexes displayed significant preference for more assertive individuals of the opposite sex in preference tests. loterspecitic aggression Because individuals of most species appear to compete with members of other species for at least some resources, aggressive abi I ity could function In interspecific as wel I as intraspecific Interactions. Peromyscus manjculatus appears to compete with other species In many parts of its range (Drickamer, 1978; Holbrook, 1978; Kritzman, 1974; Redfield, Krebs, & Taitt, 1977), and E..... pol jonotus often appears to compete with M.u.s musculus for food (Briese & Smith, 1973; Caldwel I & Gentry, 1966a). Aggressive competition for resources is also common In Microtus; for example: M.... agrestes appears to compete with M.... arval is for resources (Dienske, 1979), while both of these species may at times be in competition with Clethrionomys gfareolus (DeJonge, 1979); M..... Iongjcaudus appears to be excluded from Its preferred habitat by~montanus in some localities
PAGE 116

109 resources, and individuals with high aggressive ability would be expected to fare better in this competition than individuals of low aggressive abi I ity, and thus to be preferred as mates. lnterspecitic competition could, therefore, function to maintain choice for aggressive mates in many species--including those that may not exhibit high levels of intraspecific aggression. Early breeding Earlier breed ins (Darwin, 1874) is probably not a consideration in the preference displayed for aggressive mates by .E...... pol jonotus, but may be of some importance to .E...... maniculatus. It is uni ikely that early breeding is an important factor to .E...... pol jonotus. Although .E...... pol ionotus display breeding peaks and decl Ines they do not appear to be seasonal breeders (Davenport, 1964; Smith, 1966). Therefore, although some seasons may be better for breeding than others (Smith & McGinnis, 1968), an individual can not really get an "earlier start" in breeding than others in the population. Peromyscus maniculatus on the other hand do appear to be seasonal breeders, and also form large winter aggregations that may contain unrelated adults (Howard, 1949). ibre-aggressive individuals might be capable of initiating breeding earlier than less-aggressive individuals after dispersal from winter aggregations when competition for resources is I ikely to be intense (Healey, 1967; Taitt, 1981). Bruce effect Exposure of females to unfamiliar males may result in pregnancy blockage
PAGE 117

110 effect", and several explanations have been offered for it. Many of these hypotheses have been reviewed by Schwagmeyer (1979), who has proposed that "females are, in effect, selecting one mate In preference to another when pregnancy blockage occurs. One would therefore predict that the Bruce effect would be I imited to circumstances In which the benefits from mating with the new male outweigh any cost of the delay In parturition or physiological effects involved" (p. 934). This argument has recently been extended by Huck, Soltis, and Coopersmith (1982). These investigators observed that dominant male house mice (MJ.i.s. muscu!us) significantly reduced the survival of strange pups, whereas subordinate males did not, and that dominant males would copulate with a female after kil I ing her I ltter. Previous Investigators (Hrdy, 1979; Labov, 1980; Mallory & Brooks, 1980) had suggested that, in species in which males committed Infanticide, It would be less costly for females to block pregnancy and mate with a strange male than to lose the I itter later through infanticide. Fol lowing these suggestions, their own observations, and the observation by Huck (1982) that dominant males are more effective in initiating pregnancy blockage; Huck et al.(1982) proposed that it ls most advantageous for females to display pregnancy blocks when confronted with dominant rather than subordinate males because they face the greatest risk of Infanticide by these males. As stated by Schwagmeyer (1979), by displaying pregnancy blocks females are In effect displaying a preference to mate with aggressive males; and the Bruce effect would be adaptive in this context as long as the costs of postponing the current I itter were outweighed by the benefits derived

PAGE 118

111 from mating with a male of high aggressive abi I ity. The Bruce effect, I ike the inciting behavior of female elephant seals (Cox, 1981; Cox & LeBeout, 1977), may be a means by which a female ensures that she mates with males with high aggressive abi I lty. Heritable aggressive ability The benefits of selecting mates with high aggressive abi I ity that have been discussed to this point are not dependent upon any component of an animal's aggressive behavior being heritable. The expression of many of the components of aggressive behavior has, however, been demonstrated to be at least partially under genetic control (Scott, 1966; Scott & Frederickson, 1951; Simon, 1979). The components of aggression may be divided into two major categories: components related to the tendency tor an animal to display aggression, or its "aggressiveness" and components related to the abi I ity of an animal to effectively perform aggressive behaviors. The validity of this division is supported by research reviewed and discussed by Scott (1966), and by Scott anrj Frederickson (1951). As stated by Scott (1966) "Heredity produces important differences in fighting behavior between mouse strains, some being more east ly excited to fight than others and some strains being more capable of winning than others" (p. 691). Although an animal's tendency toward aggression and Its abi I lty to perform aggressive behavior effectively may be separable, they would be expected to be highly positively correlated. One would expect that it would not be adaptive tor an animal to be highly prone to engage In aggressive encounters If it stood I lttle chance of winning those

PAGE 119

112 encounters; nor on the other hand would it be expected to be adaptive for an animal to be completely unprovokable if it had high aggressive abi I ity. Because fights involve potential costs as wel I as potential benefits (Maynard Smith, 1976; Maynard Smith & Price, 1973), individuals should assess opponents carefully, and fight only when they have a reasonable expectation of winning (Clutton-Brock & Albon, 1979; Clutton-Brock, Albon, Gibson & Guinness, 1979). Individuals that most frequently display aggressive behavior, therefore, should normally also be those individuals that have the highest aggressive abi I ity. If the display of aggression is an indication of an individual 1 s aggressive abil lty, then these displays may be used to evaluate that individual's potential as a mate (Cox, 1981; Cox & LeBeouf, 1977). While, as previously noted, many of the benefits that may accrue to individuals that chose mates with high aggressive abi I ity do not depend on that abi I lty being heritable, choosing aggressive mates should be even more adaptive if any of the components of aggressive abi I ity are heritable. individuals selecting aggressive mates would gain not only immediate benefits, such as better territory or defense of nest site, but "good genes" (Maynard Smith, 1956; Trivers, 1972) as wel I. (However see, Krebs & Davies, 1981; Maynard Smith, 1978, p. 170, 171; Parker, 1979, p. 146; for I imits on the use of heritable factors as a basis for choice). Selection of mates with high aggressive abi I ity may be adaptive even when such individuals do not hold the best available resources, if these Individuals are more attractive as mates, and aggressive abi I ity is heritable. This combination of conditions has

PAGE 120

113 been suggested to act to lower the polygny threshold in species (the "sexy son" hypothesis: Heisler, 1981; Weatherhead & Robertson, 1979). Some observations of Peromyscus manjcu!atus bairdl and. pol ionotus suggest that the display of aggression, or displays related to aggressive abi I ity, may provide a basis for mate selection in these species. Dewsbury's (1981b) observation that .E.i. manicu!atus females approach and solicit dominant males more frequently than subordinates in two-male copulatory tests, although open to other lntrepretations, is also consistent with this suggestion. In the present study high-aggression .E.i. pol jonotus males displayed aggressive digging more frequently than low-aggression males, and may act to prevent the display of this behavior by low-aggression males. The areas around nest sites of this species often exhibit evidence of frequent digging behavior. Although members of this species do not appear to exhibit territorial behavior (Davenport, 1964) they do defend nest burrows (Blair, 1951), and most I ikely also some of the area around burrows. The "incipient burrows" and other evidence of digging near nest burrows may provide an indication to individuals that an area Is occupied; and aggressive digging may be a means of displaying an abi I lty to construct and defend burrows. Fami I iarity as a Factor in Preference The results of the present study were not consistent with the hypothesis that members of monogamous species should display greater preference for familiar than unfaml I iar individuals, nor with the hypothesis that the effects of faml I iarity on the choice of members of polygamous species should be neg( lgible. In famll iarlty preference

PAGE 121

114 tests Individuals of both sexes of the polygamous species Eeromyscus manjculatus displayed preference for fami I tar Individuals of the opposite sex, while individuals of the monogamous species Peromyscus pol jonotus did not display preference. In addition, E..... pol jonotus did not display preference for nesting with faml I lar Individuals of the opposite sex in the seminatural experiments. Two types of factors may have influenced the behavior of P. maniculatus and~ pol lonotus in familiarity preference tests; these are 1) factors related to the prior history of the animals tested and 2) factors related to the ecology and social system of these particular species. Prior History The ability to recognize differences in the fami I iarlty of individual odors has been demonstrated in a wide variety of mammal Ian (Brown, R.E., 1979; Halpin, 1980) and non-mammal Ian (Halpin, 1980) species; and evidence exists that individuals of many rodent species may exhibit preferences based on this abi I ity (Brown, R.E., 1979). Of particular relevance to the present discussion are observations suggesting that an Individual 1 s preference for fami I iar or unfamll lar conspeciflcs may be determined in part by whether that individual previously received monogamous or polygamous mating experience. While monogamously mated female rats appear to prefer the odor of a famll iar over a novel male, polygamously mated females display no preference, polygamously mated males prefer novel females, and monogamously mated males may either display no preference or preference for novel females depending on test conditions (Carr, Krames, & Costanzo, 1970; Carr et al., 1979; Carr et al., 1980; Krames et al., 1967). The general

PAGE 122

115 tendency in these studies appears to be greater preference for faml I iar Individuals after monogamous mating experience and greater preference for novel Individuals after polygamous mating experience. Dewsbury (1979) has also observed a higher probabi I ity of mating In .E.._ .m.... bajrdj In tests in which Individuals were faml I iar (had previous monogamous mating experience) than in tests in which mates were u n f am i I i ar. Prior to famll iarity preference tests animals In the present study were h oused with a single opposite-sexed conspecific and therefore, outside the poss lb ii ity of having mated with siblings, would have had only monogamous mating opportunities prior to these tests. While pretest housing conditions may in part explain the preference for faml I iar individuals displayed by .E.._ manjculatus, they can not explain the lack of preference displayed by .E..._ pol jonotus. The lack of preference displayed by .E.... pol jonotus in the familiarity preference tests, although consistent with observations of the nesting behavior of this species in the seminatural study, Is inconsistent with predictions based on the mating system of this species. These differences In the preference off. maniculatus and .E..._ pol jonotus may be explained by differences In the ecology and social organization of these two species. Ecology and Social System Peromyscus maniculatus As noted previously breeding .E.... .m.... balrdl appear to maintain overlapping home ranges (Blair, 1940). Although breeding adults appear to aggressively limit settlement of strange juveniles in their home

PAGE 123

116 range (Ayer & Whittsett, 1980; Enders, 1978, Whitsett et al., 1979) I ittle overt aggression appears to occur between members of establ I shed populations (HII I, 1977; Terman, 1961, 1974). Lack of aggression between establ I shed residents In a population is not uncommon, and may be a result of the "dear enemy" phenomenon as described by Wilson (1975): "A territorial neighbor is not ordlnari ly a threat. It should pay to recognize him as an individual, to agree mutually upon the joint boundary, and to waste as I ittle energy as possible In host! le exchanges thereafter" (p. 273). This effect appears to occur in at least some (Healey, 1967), but not al I (Vestal & Hel lack, 1978) subspecies of .E..... manjculatus. The dear enemy phenomenon may be a factor in juvenile dispersal and settlement in .E..... maniculatus. Blair (1958) observed that the majority of juveniles in a population of .E..... manjculatus In Texas dispersed either very short distances from the natal site or not at al I; and 38 percent of the females and 28 percent of the males in a population of .E..... mi bajrdj in Michigan did not disperse from their natal home range to breed (Dice & Howard, 1951). Healey (1967) has suggested that for .E..... manjculatus "an animal's chances of breeding are severely I imlted when it moves any distance from Its birth place" (p. 388). These observations suggest that a juvenl le has the greatest probability of breeding successfully if it remains on or near the parenta I home range. In I i ght of the aggress I on directed toward unfami I iar juveniles by adults (Ayer & Whitsett, 1980; Enders, 1978; Healey, 1967; Sadleir, 1965) one of the more successful strategies for

PAGE 124

117 juvenile .E.... rnanlculatus may be to breed with its neighbors rather than to attempt to disperse and breed with unfami I iar conspecifics. Early breeding may be an additional factor acting to increase the adaptive value of selecting fami I Jar mates in this species. As Is typical of other Peromyscus (Terman, 1968), .E.... manjculatus tends to remain In a particular area once it has establ !shed Itself as a breeding resident of that area. The apparent sedentary nature of residents, and the overlapping home ranges they exhibit (Blair, 1940; Howard, 1949; Mihok, 1979; Morris, 1955), probably result in each resident breeding within a fairly wel I defined group of faml I lar conspecifics. Individuals within an area aggregate In the winter and disperse from these aggregations to breed in the spring (Howard, 1949; Metzgar, 1979). Individuals that have become famil lar In overwintering aggregations or through prior breeding may be able to pair more quickly, and establish themselves as breeders earlier in the spring than unfami I iar Individuals. Perornyscus pol ionotus Perornyscus pol jonotus are sedentary once they become resident in an area (Blair, 1951; Smith, 1966, 1968), are not seasonal breeders (Davenport, 1964; Smith, 1966; Smith & McGinnis, 1968), and exhibit a monogamous mating system In which they form long-term reproductive pairs (Blair, 1951; Foltz, 1979, 1981). In addition, members of this species are generally fairly short I ived CDapson, 1972). As a result of these factors the opportunities for members of this species to uti I ize fami I larity as a factor in mate selection during Its I ifetlme may be somewhat I lmlted. Two situations that could occur in which

PAGE 125

118 faml I larlty may be a factor In mate selection in this species would be in the initial selection of a mate upon attaining reproductive maturity, or in the selection of a new mate upon the death or incapacitation of the current mate. These possibi I ities wil I be examined in the fol lowing discussion. As in .E.... manjculatus, E.._ pol jonotus exhibit overlapping home ranges that do not appear to be defended against breeding adult conspecifics (Davenport, 1965). It Is I ikely that the majority of aggressive interactions in E.._ pol lonotus, other than possibly aggression incidental to foraging, are centered around the defense of nest sites (Blair, 1951 ). In I ight of the specific nesting requirements of this species, nest site defense would probably effectively limit juvenile recruitment into the resident breeding population since it is uni ikely that a juvenile could obtain nest sites in competition with adult conspecifics. A juvenl le could breed near the natal home range if it were able to attract a neighboring resident animal as a mate. Opportunities for a juvenile to enter a breeding relationship with a familiar resident are, however, I ikely to be very I imited. Established residents may be exposed to the choice of juvenile mates only In the event of the reproductive failure or death of their existing mates. Juveniles, however, would generally be expected to perform more poorly in competition with residents than would an adult mate. In addition a juvenile's reproductive performance is unproven, and at least for females generally below that of adults (Caldwel I & Gentry, 1965b; Smith, 1966; Wit I lams, Got fey, & Carmon, 1965). The best choice for a resident adult after the loss of a mate,

PAGE 126

119 therefore, would probably be to mate with a neighboring resident rather than a juvenile; or barring the avai labi I ity of a neighboring resident to mate with a transient adult. Although smal I groups of young sexually immature .E..... pol jonotus have been observed In the winter (Smith, 1966), it is uni lkely that familiarity from relationships in these groups has a general effect on mate selection in this species. These groups comprised less than three percent of the social groups observed by Smith (1966), and such groups were never observed by Rand and Host (1942). Smith (1968) has suggested that these groups are composed of I !tter mates that are overwintering in parental burrows. Several observations lend support to this suggestion. First, adult defense of burrows (Blair, 1951) makes it uni ikely that unrelated individuals would be tolerated In burrows. In addition, evidence reviewed by Foltz (1979) suggests that parental males may move with I itters to burrows near the natal burrow. Finally, the largest of these groups observed by Smith (1966) was composed of six individuals, which is within the range of I itter sizes reported for .E..... pol jonotus (Laffoday, 1957; Smith, 1966; Wil Iiams, Gol ley & Carmon, 1965). Kinship as a Factor 1n Preference Although inbreeding may be advantageous under certain conditions (Bengtsson, 1978; Cowan, 1979; Maynard Smith, 1978), the generally detrimental effects of inbreeding, such as inbreeding depression, have I ikely led to the evolution of mechanisms to avoid inbreeding in most species (Bixler, 1981). Evidence available for the two species of interest in the present study, .E..... manjculatus and .E..... pol ionotus,

PAGE 127

120 suggests both high and low levels of inbreeding for these species. In the fol lowing discussion evidence for and against inbreeding In these two species, and the relevant observations from the present study, wil I be discussed In the context of the ecology and social behavior of these species. inbreeding Io Peromyscus Manicuiatus Evidence tor and against Inbreeding Howard (1949) noted that in the population of .E..... m.... bairdi he he studied "There seemed to be no bar to the mating of close relatives, and parent-offspring matings and pairing between sibs occurred when conditions were such that these related mice happened to be together at the time when they became sexually active'' (p. 15). Howard (1949) estimated that up to 10 percent of the matings in the population he observed were inbred. Rasmussen (1964) has also suggested a high level of inbreeding for .E..... m.... graci I is based on the observation of a shortage of heterozygotes in the population he observed. Foltz (1979, 1981b) has, however, criticized both the Howard (1949) and Rasmussen (1964) studies on the basis of methodological flaws. This criticism seems wel I founded on the basis of evidence cited by Foltz (1979), and by observations that reproductive performance in sibl Ing matings in this species Is below that for nonsibl Ing matings (Dewsbury, 1982; Hi I I, 1974). Although differences in the preference of .E..... manjcuiatus for slbl ings and nonsibl ings In the present study were statistically non-significant, scores in the majority of comparisons were higher for nonslbl ings than for siblings; and .E..... manjcuiatus females that were not In diestrus displayed significantly greater preference for

PAGE 128

121 nonsibl Ing males than did females in dlestrus. These observations are consistent with the hypothesis that .E..,_ maniculatus should prefer nonsibl ings as mates over sibl lngs. Ecological and social factors Because .E..._ m..... baled! may exhibit inbreeding depression (Dewsbury, 1982a; HII I, 1974) individuals of this species would be expected to display stronger preference for nonsibl ings than was exhibited in the present study. The smal I differences in preference exhibited in the present study might be explained if .E..,_ m..... bairdj, although attracted to nonsibl ings as mates, are also attracted to siblings on other bases. It might be adaptive for slbl ings to be attracted to one another if by remaining together they were able to increase direct benefits to themselves (e. g., through increased survival), or if such behavior resulted in an increase in their inclusive fitness (Hamilton, W. D., 1964, a, b). At least two factors in the behavior of .E..._ m..... bajrdj make it probable that they wil I maintain extensive contact with relatives, including siblings, and thereby provide opportunities for kin selected behavior in this species. First, .E..._ m..... baled! tend to disperse short distances from their birthplace before establishing a home range (Dice & Howard, 1951; Howard, 1949). It is I ikely therefore that many of the residents in a population wi I I have settled near relatives. In addition, because winter aggregations may include nearby residents (Howard, 1949), it is I ikely that at least some of these relatives are I ikely to overwinter together. Participation in winter aggregations may greatly increase an individual's probabi I ity of surviving unti I the spring breeding season

PAGE 129

122 (Howard, 1951). The abi I lty to remain in aggregations through the winter appears to depend largely on the avai labi I ity of adequate food to maintain the aggregated mice (Howard, 1951). Although mice could venture out of aggregations to forage, this behavior would be somewhat self-defeating. Food items wll I I lkely be scarce in winter months and difficult to find, and increased exposure to cold during foraging wil I result in increased heat loss, making it necessary to forage even more intensely to gather sufficient food to maintain body temperature at an adequate level. The amount of food cached near an aggregation of .E..,_ m.... bajrdj may therefore determine how successfully members of that aggregation survive the winter. Although information is not available as to what factors determine where aggregations are formed, the nucleus of these aggregations is generally a parental pair and one of their I itters (Howard, 1949). It Is I ikely that parents cache food near the time of the birth of their last fal I I itter, and that the combination of this smal I aggregation and food cache may often attract additional neighboring individuals. Because many of these individuals may be related to the family group, inclusive fitness may be increased by al lowing them to join the aggregation and uti I lze the food cache. Two additional factors, however, may be of importance In this context. First, at least up to a point, Increasing the size of an aggregation may benefit al I of its members because a larger group can more easily maintain a higher temperature. This may in part explain the observation that individuals of other species are sometimes al lowed in aggregations (Howard, 1949). Second, laboratory observations (Rice, 1972; Terman, 1974) suggest

PAGE 130

123 that an existing food cache may act as a stimulus for hoarding behavior in .E..... m.... bajrdj. If individuals joining an aggregation also add to the food cache they may in effect "pay their own way" as members of the aggregation. The behaviors exhibited by at least some of the individuals in aggregations, therefore, may be mutual istic. Whether the behavior of an ind iv i dua I in an aggregation is viewed as mutual istic, or kin selected (or both), wll I depend on the costs of that behavior to the individual, and upon who receives the benefits of that behavior. The behavior of Individuals of other species in aggregations of .E..... manjculatus, for example, may be mutual istic. The costs and benefits to the resident parental pair, however, are much more complex. Costs Incurred by these animals In caching food include expenditure of time and energy, and possibly increased exposure to predators. An additional possible cost of aggregation is related to the fact that abundant food in the spring may al low pairs to breed early (Gashwiler, 1979; Taitt, 1981). If food caches are severely depleted during winter aggregation, spring breeding may be delayed for the parental pair. In return for these costs the parental pair provide benefits to themselves, their offspring, and possibly neighboring slbl ings. Kin sel e ction may therefore act as one of the factors that maintain winter aggregations in .E..... m.... bairdi, and may therefore be one of the factors that act to maintain attraction to slbl ings outside of a breeding context. Although this hypothesis is untested, the relatedness of individuals within aggregations could be assessed through electrophoretlc and trap-retrap studies.

PAGE 131

124 The tendency toward philopatry in .E...... manicu!atus may also lead to opportunities to increase inclusive fitness through cooperative breeding. C-ommunal I itters, and apparently cooperative care of these I itters, have been observed in populations of .E.... manicu!atus in Texas (Blair, 1958), Colorado (Hansen, 1957), and Michigan CG .m.... bajrdj; Howard, 1949). Many of the hypotheses on the effects of ecological and kinship factors on cooperative breedins have recently been reviewed (Koenig & Pitelka, 1981) 2nd wi I I not be discussed in detail here. The generally accepted hypothesis is "that habitat saturation provides the primary impetus for philopatry, and through it for evolution of group territoriality and cooperative breeding (Emlen, 1982, p.32). As described by Emlen (1982) "As population numbers increase, suitable habitat becomes ti I led or 'saturated'. Unoccupied territorities are rare, and territory turnovers are few. As the intensity of competition for space increases, fewer and fewer individuals are able to establish themselves on quality territories. The option of breeding independently becomes increasingly I imited" (p. 32). An additional factor that mcy mediate the occurrence of cooperative breeding in .E.... manicu!atus is the sex ratic. Howard (1949) has noted that breeding combinations with more than one individual of either sex occur in areas where the sex ratio is not equ2l. The relatedness of the individuals in these breeding groups is unknown. A reasonable hypothesis, in I ight of the social organization 2nd behavior of this species, is that under conditions of high population density and unequal sex ration, same-sexed siblings of the "surplus" sex may find it more adaptive to establish

PAGE 132

125 themselves in breeding groups with a member of the opposite sex than to attempt to gain resident breeding status on their own. Inbreeding in Peromyscus Pol ionotus Evidence for and against inbreeding Smith (1966) and Smith, Carmon, and Gentry (1972) have presented evidence that .P.... pol ionotus may be highly inbred. This finding appears to be at odds with evidence that reproductive performance in .P.... pol ionotus is positively correlated with genie heterozygosity (Smith et al., 1975). Smith et al. (1975) have suggested that the level of inbreeding in this species is I inked in an adaptive manner to population density, level of aggression, and dispersal. These investigators suggest that at low and increasing population densities levels of aggression and dispersion wil I also be low, while levels of inbreeding wil I be high. When population density rises individuals wi I I begin to outbreed more, and produce more-aggressive heterozygous offspring that are better suited to competition in the population or during dispersal. Smith (1968) has also suggested that opposite-sexed siblings display a tendency to disperse together, and has observed that the females in these sibling pairs may often be pregnant. Foltz (1979, 1981) has suggested alternative interpretations for many of the observations presented by these investigators as evidence of inbreeding In .P.... pol ionotus. These Interpretations are however only presented as alternatives, and Foltz (1979, 1981) was not able to exclude the possibi I ity of high levels of inbreeding in this species. In I ight of Smith's (1966) observation of a preference by .P.... pol ionotus females for sibling males over nonsibl ing males Foltz (1981)

PAGE 133

126 suggested a need for additional research on the mating preferences of .E....... pol ionotus. The present study indicates that females .E....... pol ionotus, as suggested by Smith (1966), display a preference for siblings. Males of this species also tend to display higher sibl Ing than nonsibl ing scores on preference measures, although their comparisons were nonsignificant. Ecological and social factors The apparent tendency toward inbreeding in .E....... polionotus (Smith, 1966, 1968; Smith, Carmon & Gentry, 1972) may be mediated by the very specific habitat requirements of this species, and the probabi I ity that Individuals must disperse long distances to find new patches of favorable environment. Shields (1982) has suggested that "if conditions existed that favored relatively faithful transmission of parental genomes, then inbreeding could be favored over both asexuality and outbreeding (p. 264) Owing to its flexibi I ity and capacity to transmit successful parantal genomes with maximum fidelity, Inbreeding is expected to be common in organisms produced by stable I ineage-environment associations" (p. 274). The very specific habitat requirements of .E....... pol ionotus may result in such a stable I ineage-environment association in this species. Because habitat requirements for this species are so specific (Rand & Host, 1942; Smith, 1966, 1968), offspring are I lkely to be most successful If they breed in areas in which conditions vary I ittle from those of their birth place.

PAGE 134

-----------------127 The patchiness of suitable envircnment for E..... pol ionotus may also predispose this species to inbreeding through selective pressures similar to those that hae been proposed to operate on Microtus pennsylvanicus (Batz Ii et al., 1977; Getz, 1978). In reference to the breeding habits of~ pennsylvanjcus Batz Ii et al. (1977) note that "Microtus pennsylvanjcus occupies smaller patches of moist meadow or marsh. Under these circumstances, strange mates may not always be avai I able, and it would be disadvantageous if siblings could not breed with one another. If Ha. pennsylvanicus must continually locate and repopulate isolated patches, the offspring of the founder(s) must mate in order to assure success." (p. 590) Similarly, for E..... pol ionotus, Smith (1968) noted that these mice are found characteristically in habitats of early stages of primary or secondary succession (Gol fey et al., 1965). For this reason it is I ikely that large distances between suitable habitat exist, and with time succession makes the habitat unsuitable for the mice. The pine forest habitats which they are associated with on the mainland are fire subcl imaxes (Laessle 1958a, 1958b; Smith, 1966) and utilization of available habitat might require c0.rtain individuals to disperse long distances to find recently burned areas. (p. 49) Smith (1968), as noted previously in this discussion, has also observed a tendency for opposite-sexed sibling pairs of E..... pol ionotus in breeding condition to disperse together. Bateson (1978, 1979) has suggested that animals learn characteristics of parents and siblings, and then use this information to choose individuals that are only slightly different from kin as mates. Gi Ider and Slater (1978) have observed behavior in mice that appears to conform to this rule, and asimilar rule of thumb may provide a basis for the apparently cyclic preference for siblings

PAGE 135

128 observed by Smith et al. (1972). The cycl le changes in slbl ing preference that may occur In this species could be generated by the rule "choose sibl lngs as mates if they are not fQ.Q similar". For .E.... pol jonotus this may mean "prefer siblings as mates as long as your parents were not the product of a sibl Ing mating". Garten (1976) has observed a positive correlation between aggression and genie heterozygosity in .E.... pol jonotus, and (Garten, 1977) between genie heterozygosity and exploratory behavior. As offspring from nonsibl ing matings are more heterozygous than offspring from sibling matings, offspring from nonsibl ing matings should be more I ikely to disperse. In I ight of the previous discussion on the patchiness of the environment for this species, It may be adaptive for them to disperse to new breeding habitat as slbl ing pairs (as observed by Smith, 1966) and for offspring of these pairs to breed with slbl ings. Smith et al. (1975) have observed low levels of heterozygosity In .E.... pol jonotus populations at low and early stages of increase In populati~n density, which may indicate that Individuals at this stage of population growth may In fact be inbreedfng. The offspring of the second generation in the new habitat, however, being the offspring of Inbred parents, would be expected to choose nonslbl ings as mates. As the population density peaked many of the offspring from these outbred matrngs would be expected to dfsperse with siblings and renew the cycle. At the stages of late population rise and early decline then, the leve l of heterozygosity In the population would be expected to be relatively high, as observed by Smith et al. ( 1975)

PAGE 136

129 Evolutlon of Monogamy In Peromyscus Pol lonotus Peromyscus pol lonotus ls morphologically more slmi lar to the "prairie forms" of .P..... manjculatus (e.g. E.i. m.a. balrdl or f .!!! pa I I escens) than to the "forest forms" of this species (Hooper, 1968), and most I ikely originated from one of the prairie forms of .P..... manlculatus during the Pleistocene interglacial stages (Blair, 1950). As discussed previously, although .P..... pol jonotus and f. manlculatus are closely related, and display similarities in a number of aspects ranging from habitat preference and morphology to behavior, they exhibit large differences in social organization and mating system. The evolutionary divergence in the social behavior and mating systems of .E.... pol jonotus and the prairie forms of .E.... manlculatus, such as ..!!). bairdi, may be explained through examination of the differences In the amount of and distribution of suitable habitat for these taxa, and differences In climate In the present day distribution of these taxa. Blair (1950) and Smith (1966) have described the factors that apparently have led to the existing distribution of .P..... pol jonotus, and Its separation from the parental species .E... manjculatus. The present geographic relationships of these two species can be explained if we assume continuous distribution of manlculatus across the coastal plain In Pleistocene time. This distribution possibly, but not necessarlty, might have been only in a narrow strip along the Gulf beaches. With encroachment of the Gulf on the land during Pleistocene Inter-glacial stages, there was the opportunity for a part of this population to be isolated In Florida, for parts of Florida projected as Islands during these periods (see Cooke, 1939). The postulated coastal-plain population of manfculatus disappeared eastward of Texas, effectively Isolating the Florida populatlon. (Blair, 1950, p. 266)

PAGE 137

130 Certain soi I characteristics appeared to be Important n I imlting the distribution of mice. In relatively undisturbed habitats, the mice occurred primarily on tine sand Deposits of sorted sands have been laid down In several ways in Florida (Laessle, 1958b). Wind was an important agent along the beach dunes. The action of water was Important along the flood plains of large rivers, the shoreI Ines of lakes and Islands, and submerged offshore bars. Al I areas above the current water level were at one time part of the Florida shoreline. As the water level fel I during glacial periods, numerous deposits of fine textured sand were gradually exposed. Their continuity was later destroyed by erosion (Alt and Brooks, 1965). These deposits and their associated vegetation are frequently widely spaced with the intervening habitat unsuitable for the old field mouse. These interrupted sand deposits are ecological islands for this species (Smith, 1966, p. 13-15) The climate In Florida would have been much cooler during the Pleistocene glaciations than at present, and may have been at least somewhat similar to conditions under which .E.i. m.... bajrdl exists presently. Assuming that the Pleistocene prairie forms of .E.i. manjcuiatus would share many characteristics with present day prairie forms of .E.i. manjculatus, one may hypothesize that many of the characteristics of the species ancestral to .E.... poijonotus may presently be exhibited by .E.i. m.... balrdj. Among these characteristics would be the abi I ity to construct shallow burrows (Houtcooper, 1972), tendency to form winter aggregations (Howard, 1949) and to cache food for winter use (Hamilton, W. J., 1943; Howard, 1949), and possibly a predisposition under some conditions to form exclusive reproductive pairs (Howard, 1949). Food caches and winter aggregations may have been as adaptive for the ancestral stock .E..... poi ionotus was derived from as they appear to be for .E.i. m.... bajrdj today (Howard, 1951). As the glaciers

PAGE 138

131 retreated and the cl !mate warmed, however, the function of these habits may have changed. The loose sand soils available may have al lowed the ancestral .E.... pol jonotus to construct deeper burrows than Its predecessors. This factor, and a warmer cl !mate, would have al lowed the ancestral species to maintain a favorable temperature in nest burrows year-round, and would probably have resulted In lower mortality. The advent of more constant nest conditions would have in turn reduced the necessity for large winter aggregations as it would be more I ikely that a family unit (parents and offspring) could maintain an adequate nest temperature alone. More constant nest burrow conditions and warmer cl !mate would also act to reduce the need for large food caches for winter survival. Food caches may, however, also serve another function. Peromyscus manjculatus, although normally a seasonal breeder, Is capable of breeding through the winter If adequate food Is available (Linduska, 1942; Taitt, 1981). Conditions of more moderate and stable temperature, along with an Increased probabi I ity of an adequate winter food supply, are I lkely to have increased the possibi I ity for successful year-round breeding In .E.... pol jonotus. The capacity of winter breeding would further act to I lmit winter aggregations to immediate faml ly, because It would be more adaptive to use food caches to produce additional offspring, than to use these resources to increase Inclusive fitness through supporting more distant relatives. The possibll ity of breeding continuously, In conjunction with ecological factors, may have provided a basis for the establ lshment of monogamy as the predominant mating behavior in .E.... pol fonotus. The

PAGE 139

132 major ecological factors of importance to monogamy in this species, as discussed previously, appear to be the availabi I ity and distribution of nest sites and food items. Constructing deep nest burrows I imits choice of breeding areas; and caching of food suggests that food may be only seasonally abundant, with more food available than necessary for survival and breeding in warmer months, and a reduced food supply in winter months. Distribution and availabi I lty of nest sites and food Items may act, as discussed earl !er, to I lmit possibilities for polygamous matings by males. Constructing deep nest burrows and provisioning food caches, however, provide a stable breeding environment for .E... pol jonotus. A longer breeding season would al low females to produce more offspring. Through investment in burrows and food caches, males may have been able to increase the number of offspring they produced by pairing with a single female, to above that they would have expected by mating polygamously. Although this shift in the behavior of ancestral .E..... pol jonotus males could be interpreted as "investment in offspring'' in a very broad sense, these behaviors do not really go beyond those presently practiced by polygamous .E..... m.... bairdi males, who also maintain nests and cache food that may be used by mates and offspring. The major shift that occurred in Individuals of the ancestral species may rather be Interpreted as a shift in emphasis from behavior resulting in increased inclusive fitness through benefits to distant relatives, to a I Imitation of these same benefits to offspring and to Increased productivity by male-female pairs. This, of course, does not preclude the possibl I ity that improved male care of offspring could have been a factor that added to the adaptive value of

PAGE 140

133 exclusive breeding relationships in .E_._ pol ionotus, but suggests that such behavior may not have been necessary for the evolution of monogamy In this species. Summary The present study is consistent with the hypothesis that aggressive abl I tty may serve as a basis in mate selection for both sexes In monogamous as wel I as non-monogamous species. In a seminatural setting aggressive Interactions occurred frequently between members of both sexes of the monogamous species .E_._ pol jonotus, and individuals within groups appeared to form stable aggressive relationships. Males of this species exhibited a behavior, aggressive digging, that may function to signal their aggressive status to females. Individuals of this species of both sexes nested more frequently with opposite-sexed Individuals that exhibited high rather than low aggressive abl I tty. Male and female .E_._ pol jonotus, and male and female .E_._ manlculatus, also exhibited evidence of preference for more assertive opposite-sexed Individuals (high rather than low tendency to interact) when tested in a preference apparatus. Preference for individuals of high aggressive abi I ity appears to be adaptive in terms of the ecology and social system of these two species. In .E_._ pol ionotus high aggressive abil tty may insure that an individual Is able to obtain I lmlted nest sites and food and defend them against conspeciflcs. Female aggression could also be a factor acting to maintain monogamy In this species (see: Kleiman, 1977; Whittenberger, 1979, 1981; Whlttenberger & Tilson, 1980). Females of this species, however, do not appear to be dominant over males (see

PAGE 141

134 Smith, 1966). Peromyscus manjculatus of both sexes appear to utilize aggressive abi I ity to I imit settlement of juveniles on their home range (Ayer & Whitsett, 1980; Enders, 1978; Fordham, 1971; Taitt, 1981; Whitsett et al., 1979). Aggressive abi I ity is also Important in male-male competition in .E.... manjculatus (Blair & Howard, 1944; Dewsbury, 1981c). Although in order for it to be adaptive to choose mates with high aggressive abi I ity it ls not necessary for aggressive abi I ity to be heritable, the adaptiveness of such choice would be expected to increase if components of this abi I ity were heritable. In preference tests fami I iarity appeared to be an important factor to individuals of both sexes of the polygamous species .E.... manjcu!atus, but of I ittle consequence to individuals of either sex of the monogamous .E.... pol jonotus. The lack of significant preference for fami I lar individuals by .E.... pol lonotus In preference tests was consistent with observations of the nesting behavior of this species in the seminatural apparatus. Although the preferences displayed by .P.... manjculatus could be a result of housing conditions prior to fami I iarity tests (Carr, Krames & Costanzo, 1970; Carr et al., 1979; Carr et al., 1980; Krames et al., 1967), these conditions do not appear to provide an explanation for the lack of preference displayed by .P.... pol jonotus. Differences in the responses of P. manlculatus and .E.... pol jonotus to famll iar individuals In preference tests may be based on differences in the opportunities Individuals of these two species have to make use of this factor in mate selection. As a result of factors of ecology, social behavior, and breeding system, these opportunities may be much more I lmited for .E.... pol jonotus than for .P....

PAGE 142

135 manjculat.u.s_. Fami I larity may, however, aid in maintaining pair bonds in .E.... pol jonotus through reducing aggression, as famll iarity did appear to reduce aggression between fami I iar opposite-sexed individuals In semlnatural experiments. Although only .E.... pol jonotus females demonstrated a significant preference for slbl ings over nonsibl ings, males of this species also tended to display higher sibl Ing than nonsibl ing scores in preference tests. This finding is consistent with the observation by Smith (1966) that female .E.... pol jonotus appear to prefer siblings as mates over nonslbl ings. Peromyscus manjculatus of both sexes displayed only nonsignificantly higher scores for nonsibl ings than for slbl ings in preference tests. Inbreeding In .E.... polionotus may be an adaptive strategy that permits individuals of this species to found populations in Isolated patches of favorable habitat. A similar strategy has previously been proposed for Microtus pennsylvanjcus (Batz I I et al., 1977; Getz, 1978). The lack of significant preference for nonsibl ings demonstrated by .E.... manjculatus, a polygamous species, may be due to competing preference responses In this species. Although .E.... manjculatus appear to avoid breeding with sibl lngs (Hi 11, 1974; Dewsbury, 1982a), Individuals may also be attracted to relatives through a preference for mating on or near their natal home range, and through opportunities to increase their inclusive fitness through interactions with relatives. The shift from polygamy to monogamy In ancestral .E.... pol jonotus may have occurred as a result of a shift from an emphasis on aggressively limiting settlement on home ranges to defense of the nest site, concomitant with a shift away from Increasing Inclusive

PAGE 143

136 fitness through aid to distant relatives to Increasing personal fitness through I imlting aid to a single mate.

PAGE 144

REFERENCES Adler, N. T. On the mechanisms of sexual behavior and their evolutionary constraints. In J. B. Hutchison (Ed.) Biological determinants Qf sexual behavior. New York: Wiley, 1978. 0 Agren, G. Social and territorial behaviour in the mongol ian gerbil conditions. Biology 0
PAGE 145

138 Baker, R. H. Habitats and distribution. In J. A. King (Ed.) Biology Q.f. Peromyscus (Rodentja). Lawrence, Kansas: American Society of ~ammalogists, 1968. Barnett, S. A., Evans, C. S., & Stoddart, R. C. Influence of females on conflict among wi Id rats. Journal Qf Zoology, 1968, ill., 391-396. Bateman, A. J. Intra-sexual selection in Drosophl I ia. Heredity. 1948, 2., 349-368. Bateson, P. Sexual imprinting and optimal outbreeding. Nature, 1978, 273, 659-660. Bateson, P. How do sensitive periods arise and what are they for? Ani m al Behaviour, 1979, 27, 470-486. Bateson, P. Optimal outbreeding and the development of sexual preferences in Japanese quai I. Zejtschrift .t..Y.r. Tierpsychology, 1980, 22., 231-244. Batz Ii, G. 0., Getz, L. L., & Hurley, S. S. Suppression of growth and reproduction of microtine rodents by social factors. Journal Qf M amma I ogy. 1977, 28. 583-591 B ediz, G. M ., & \ hitsett, J. M Social inhibition of sexual maturation in male prairie deer mice. Journal Qf Comparative .a.!ld. Physiological Psychology, 1979, 21, 493-500. Bengtsson, B. 0. Avoid inbreeding: At what cost? Journal of Theoretical Biology, 1978, D..., 439-444. Bertram, B. C. R. Social factors influencing reproduction in wi Id I ions. Journal Qf Zoology. 1975, 111., 463-482. Bertram, B. C. R. Kin selection in I ions and in evolution. In P. P. G. Bateson & R. A. Hinde (Eds.) Growing points l.n ethology. Cambridge: Cambridge University Press, 1976. Birdsal I, D. A., & Nash, D. Occurrence of successful multiple insemination of females in natural populations of deer mice CPeromyscus manjculatus). Evolution, 1973, 21., 106-110.

PAGE 146

139 Bixler, R. H. The incest controversy. Psychological Reports, 1981, .4.2., 267-283. Blair, W. F. Michigan. A study of pra1r1e deer-mouse populations In southern American Midland Naturalist, 1940, ZA., 273-305. Blair, W. F. Size of home range and notes on the I ife history of the woodland deer-mouse and eastern chipmunk in northern Michigan. Journal Qf Mammalogy, 1942, Zi, 27-36. Blair, W. F. Populations of the deer-mouse and associated smal I mammals in the mesquite association of southern New Mexico. Contributions from the Laboratory of Vertebrate Biology, University of Michigan, Ann Arbor, 1943, 21., 1-40. Blair, W. F. Ecological factors in the speciation of Peromyscus. Evolution, 1950, ~, 253-275. Blair, W. F. Population structure, social behavior, and environmental relations in a natural population of the beach mouse (Peromyscus pol ionotus leucocepbalus). Contributions from the Laboratory of Vertebrate Biology. University of Michigan, Ann Arbor, 1951, .48., 1-47. Blair, W. F. Effects of x-irradiation on a natural population of the deer mouse (Peromyscus maniculatus). Ecology, 1958, N, 113-118. Blair, W. F., & Howard, W. E. Experimental evidence of sexual isolation between three forms of the cenospecies Peromyscus maniculatus. Contributions from the Laboratory of Vertebrate Biology, University of Mi chi gan, Ann Arbor, MI 1 944, 2-Q, 1 -1 9. Boice, R. Burrows of wild and albino rats: Effects of domestication, outdoor raising, age, experience and maternal state. Journal of Comparative and Physiological Psychology, 1977, 91, 649-661. Boice, R., & Adams, N. Outdoor enclosures for feral izing rats and mice. Behavior Research Methods & Instrumentation, 1980, 12., 577-582. Borgia, G. Sexual selection and the evolution of mating systems. In M. S. Blum & N. A. Blum (Eds.) Sexual selection and reproductive competition~ insects. New York: Academic Press Inc., 1979.

PAGE 147

140 Bowen, D. W., & Brooks, R. J. Social organization of confined male collared lemmings CDicrostonyx groenlandicus Trai I I). Animal Behaviour, 1978, ZQ., 1126-1135. Brain, P. F., Benton, D., & Bolton, J. C. Comparison of agonistic behavior in individually housed male mice with those cohabiting with females. Aggressive Behavior, 1978, !, 201-206. Briese, L. A., & Smith, M. H. Competition between MJJ.S. musculus .and. Peromyscus pol ionotus. Journal .Qi Mammalogy, 1973, 24., 968-969. Brown, J. L. The evolution of diversity in avian territorial systems. I'/ i I son Bu I I et in, 1 964, Th, 161-169. Brown, J. L. Im! evolution Q.f behavior. New York: W. W. Norton & Company, Inc. 1975. Brown, R. E. Mammalian social odors: A critical review. In Advances l.n study .Q.f behavior (Vol. 10). New York: Academic Press, 1979. Bruce, H. M. An exteroceptive block to pregnancy in the mouse. Nature, 1959, 1M, 105. Bruce, H. M. A block to pregnancy in the mouse caused by the proximity of strange males. Journal Qf Reproduction .an..d. Ferti I ity. 1960, 1, 96-103. Bulmer, M. G. Inbreeding In the great tit. Heredity. 1973, lQ., 313-325. Burley, N. Parental investment, mate choice, and mate qual lty. Proceedings the Nati ona I Academy Science, 1977, 7 4, 3476-3479. Burley, N. Mate choice by multiple criteria in a monogamous species. American Naturalist, 1981, ill, 515-528. Caldwel I, L. D., & Gentry, J.B. in a one-acre field enclosure. Interactions of Peromyscus and M.u..s. Ecology, 1965, 4Q., 189-192. Ca)

PAGE 148

141 Caldwel I, L. D., & Gentry, J. B. Natality in Peromyscus pol ionotus populations. American Midland Naturalist, 1965, :zA., 168-175. Cb) Carmichael, M. S. Sexual discrimination by golden hamsters (Mesocricetus auratus). Behavioral and Neural Biology, 1980, 2.2., 73-90. Carr, W. J., Demesquita-Wander, M., Sachs, S. R., & Maconi, P. Responses of female rats to odors from fami I iar vs. novel males. Bui letin .oi .1b..e. Psychonomic Society. 1979, 1.A., 118-1120. Carr, W. J., Hirsch, J. T., & Balazs, J. M. Responses of male rats to odors from fami I iar vs. novel females. Behavioral .aru1 Neural Biology. 1980, 22., 331-337. Carr, W. J., Krames, L., & Costanzo, D. J. Previous sexual experience and olfactory preference for novel versus original sex partners in rats. Journal of Comparative and Physiological Psychology, 1970, 1.1, 216-222. Carr, W. J., Martorano, R. D., & Krames, L. Responses of mice to odors associated with stress. Journal 2f_ Comparative and Physiological Psychology, 1970, 1.1, 223-228. Carr, W. J., Wylie, N. R., & Loeb, L. S. Responses of adult and immature rats to sex odors. Journal of Comparative and Physiological Psychology_, 1970, 12., 51-59. Clutton-Brock, T. H., & Harvey, P. H. Primate ecology and social organization. Journal .oi Zoology, 1977, ill, 1-39. Glutton-Brock, T. H., & Harvey, P. H. Mammals, resources and reproductive strategies. Nature, 1978, 21.2, 191-195. Glutton-Brock, T. H., & Albon, S. D. The roaring of red deer and the evolution of honest advertisement. Behaviour, 1979, 6.2, 145-170. Glutton-Brock, T. H., Albon, S. D., Gibson, R. M., & Guinness, F. E. The logical stag: Adaptive aspects of fighting In red deer CCervus elaphus .LJ. Animal Behaviour, 1979, ll, 211-225.

PAGE 149

142 Cogshal I, A. S. Food habits of deer mice of the genus Peromyscus in captivity. Journal .Qi Mammalogy, 1928, 2, 217-221. Colvin, D. V. Agonistic behavior in males of five species of voles Microtus. Animal Behavior, 1973, 21, 471-480. Cooke, C. W. Scenery of Florida interpreted by a geologist. Florida Geological Bulletin, 1939, 11., 1-118. Costanzo, D. J., & Renfrew, J. Preference of female rats for odors of dominant versus subordinate males. Paper presented at the meetings of the Psychonomic Society, \vashington, D.C. 1977. Coulson, J. C. The influence of the pair-bond and age on the breeding biology of the kittiwake gul I R.Ls..a trjdactyla. Journal of Animal Ecology, 1966, 12., 269-279. Cowan, D. P. Sib I ing mating in a hunting wasp: Adaptive inbreeding? Science, 1979, 2Q2., 1403-1405. Cox, C. R. Agonistlc encounters among male elephant seals: Frequency, context, and the role of female preference. American Zoologist, 1981, 21, 197-209. Cox, C. R., & LeBoeuf, B. J. Female incitation of male competition: A mechanism in sexual selection. American Naturalist, 1977, 11.1_, 317-335. Crook, J. H. On the integration of gender strategies In mammalian social systems. In J. S. Rosenblatt & B. R. Komisaruk (Eds.) Reproductive behavior and evolution. New York: Plenum Press, 1977. Crowcroft, P., & Rowe, F. P. Social organization and territorial behavior in the wild house mouse
PAGE 150

143 Darwin, C. origin Qf species. London: John Murray, 1859. Darwin, C. The descent Q.f_ man; And selection ln relation 1Q Second ed., London: John Murray, 1874. Davenport, L. B., Jr. Structure of two Peromyscus pol jonotus populations in old-field ecosystems at the AEC Savannah River Plant. Journal Q.f_ Mammalogy, 1964, 42., 95-113. Davis, J. W. F., & O 1 Donald, P. Territory size, breeding time, and mating preference in the Arctic skua. Nature, 1976, 2.QQ., 774-775. Dawkins, R. The selfish gene. Oxford: Oxford University Press, 1976. de Catanzaro, D. Facilitation of intermale aggression in mice through exposure to receptive females. Journal Q.f_ Comparative and Physiological Psychology, 1981, 92., 638-645. DeJon g e, G. Response to con and heterospecific male odors by the voles M icrotus agrestis, M.... arvalis and Clethrionomys glareolus with respect to competition for space. Behaviour, 1980, ll, 277-303. Dewsbury, D. A. The use of muroid rodents in the psychology laboratory. Behavior Research M ethods~ Instrumentation, 1974, g_, 301-308. Dewsbury, D. A. The comparative method in studies of reproductive behavior. In T. E. I J cG i 11, D. A. Dewsbury, & B. D. Sachs (Eds.) .9.Il.d_ Behavior. New Yori<: Plenum Publishing Corporation, 1978. Dewsbury, D. A. Copulctory behavior of deer mice (Peromyscus maniculatus): 11. A study of some factors regulating the fine structure of behavior. Journal Qf Comparative .Qlli!_ Physjologjcal Psychology. 1979, 22., 161-177. Dewsbury, D. A. An exercise in the prediction of monogamy in the field from laboratory data on 42 species of muroid rodents. Biologist, 1981, hl, 138-162. Ca> Dewsbury, D. A. Effects of novelty on copulatory behavior: The Coolidge effect and related phenanena. Psychological Bui letin, 1981, 8..2_, 464-482. Cb)

PAGE 151

144 Dewsbury, D. A. Social dominance, copulatory behavior, and differential reproduction in deer mice (Peromyscus maniculatus>. Journal Qf Comparative@ Physiological Psychology, 1981, 22., 880-895. Cc) Dewsbury, D. A. Avoidance of incestuous breeding between siblings in two species of Peromyscus mice. Biology of Behavior, 1982, I, 1 57 -169. (a) Dewsbury, D. A. reproduction. Dominance rank, copulatory behavior, and differential Quarterly Review Qf Biology, 1982, 21., 135-159. Cb) Dewsbury, D. A. Ejaculate cost and male choice. American Naturalist, 1982, ll.2., 601-610. Cc) Dewsbury, D. A., & Baumgardner, D. J. Studies of sperm competition in two species of muroid rodents. Behavioral Ecology and Sociobiology, 1981, 2, 121-133. Dewsbury, D. A., & Reth I ingshafer, D. A. Comparative psychology: A modern survey. New York: M cGraw-Hi I I, 1973. Dice, L. R. Some factors affecting the distribution of the pra1r1e vole, forest deer mouse, and prairie deer mouse. Ecology. 1922, 1, 29-47. Dice, L. R., & Howard, E. Distance of dispersal by prairie deermice from birthplaces to breeding sites. Contributions from~ Laboratory Qf Vertebrate Biology, University of ~ ichigan, Ann Arbor, MI, 1 951 2.Q_, 1-15. Dienske, H. The importance of social interactions and habitat in cooipetition between Microtus a grestis and & arval is. Behaviour, 197 9, ZL 1-126. Drickamer, L. C. Annual reproduction patterns in populations of two sympatric species of Peromyscus. Behavioral Biology. 1978, 22, 405-408. Drickamer, L. C. Acceleration and delay of first estrus in wild~ musculus. Journal Qf Mammalogy, 1979, 6..Q., 215-216.

PAGE 152

145 Eisenberg, J. F. Studies on the behavior of Peromyscus maniculatus gambel i I and Peromyscus cal ifornlcus parasitlcus. Behaviour, 1962, 12., 177-207. Eisenberg, J. F. The evolution of the reproductive unit In the class mammal ia. In J. S. Rosenblatt & B. R. Komlsaruk (Eds.) Reproductive behavior .aru1 evolution. New York: Plenum Pub I ishing Corporation, 1977. Emlen, S. T. The evolution of helping. I. An ecological constraints model. American Naturalist, 1982, 11.2., 29-53. Emlen, S. T., & Oring, L. W. Ecology, sexual selection, and the evolution of mating systems. Science, 1977, ill, 215-223. Enders, J. E. Social Interactions between confined juvenile and adult Peromyscus maniculatus bairdli: Effects of social factors on juvenile settlement and growth. (Doctoral dissertation, Michigan State University, 1977). Dissertation Abstracts International, 1978, 28_, 46808-46818. (University Microfilms No. 780341) Epple, G. The role of pheromones in the social communication of marmoset monkeys. Journal _Qf Reproduction and Fertl I ity Supplement, 1973, 12., 447-454. Epple, G. Olfactory communication in South American primates. Annals N....Y... Academy .O.f. Science, 1974, m, 261-278. Erickson, C. J., & Zenone, P. G. doves: Avoidance of cuckoldry? Courtship differences in male ring Science, 1976, 122., 1353-1354. Fairbairn, D. J. Why breed early? A study of reproductive tactics in Peromyscus. Canadian Journal -21 Zoology, 1977, 52., 862-871. Fairbairn, D. J. manlculatus). Behavior of dispersing deer mice
PAGE 153

146 Fass, B., Guterman, P. E., & Stevens, D. A. Evidence that rats discriminate between famll iar and unfaml I iar putative urinary oderants of adult male conspeclflcs. Aggressive Behavior, 1978, 4., 231-236. Fisher, R. A. The genetical theory of natural selection. New York: Dover, 1958. Flannel ly, K., & Lore, R. The influence of females upon aggression in domesticated male rats (Rattus norveglcus). Animal Behaviour, 1977, .2..2., 651-659. Foltz, D. W. Genetics and mating system of the oldfleld mouse (Peromyscus pol lonotus). (Doctoral dissertation, University of Michigan, 1979). Dissertation Abstracts International, 1980, .4.Q, 46928-46938. (University Microfilms No. 8007739) Foltz, D. W. Genetic evidence for long-term monogamy in a smal I rodent, Peromyscus pol lonotus. American Naturalist. 1981. ill, 665-675. (a) Foltz, D. W. Genetic measures of inbreeding in Peromyscus. Journal Qf Mammalogy. 1981, 62.., 470-476. (b) Fordham, R. A. Field populations of deermlce with supplemental food. Ecology. 1972, 22., 138-146. Garson, P. J. Social interactions of woodmice (Apodemus sylvatjcus) studied by direct observation in the wild. Journal Qf Zoology, 1975, ill, 496-500. Garten, C. T., Jr. Relationships between aggressive behavior and genie heterozygoslty in the oldfield mouse Peromyscus pol jonotus. Evolution, 1976, N, 59-72. Garten, C. T., Jr. Relationships between exploratory behaviour and genie heterozygosity in the oldfield mouse. Animal Behaviour, 1977, .2..2., 328-332. Gashw I I er, J. S. tree seed crop. Deer mouse reproduction and its relationship to the American Midland Natural 1st, 1979, .1..Q2., 95-104.

PAGE 154

147 Gentry, J. B. Invasion of a one-year abandoned field by Peromyscus pol lonotus and Mus musculus. Journal of Mammalogy, 1966, .41, 431-439. Gentry, J. B., & Smith, M. H. Food habits and burrow associates of Peromyscus pol lonotus. Journal~ Mammalogy, 1968, .4.2., 562-565. Getz. L. L. Speculation on social structure and population cycles of microtine rodents. Biologist, 1978, fill, 134-147. Getz, L. L., & Carter, C. S. Social organization in Mjcrotus ochrogaster populations. Biologist, 1980, QZ, 56-69. Getz, L. L., Carter, C. S., & Gavish, L. The mating system of the prairie vole, Mjcrotus ochrogaster: Field and laboratory evidence for pair-bonding. Behavioral Ecology and Sociobiology, 1981, 8., 189-194. Gi Ider, P. M., & Slater, P. J. B. Interest of mice in conspecific male odors is influenced by degree of kinship. Nature, 1978, ill, 364-365. Gipps, J. H., & Jewel I, P. A. Maintaining populations of bank voles, Clethrionomys glareolus, in large outdoor enclosures, and measuring the response of population variables to the castration of males. Journal Qf Animal Ecology, 1979, 46., 535-555. Goforth, W., & Baskett, T. Social organization of penned Mourning doves. fillk, 1971, 8..8., 528-542. Golley, F. B., Gentry, J.B., Caldwell, L. D., & Davenport, L.B., Jr. Number and variety of smal I mammals on the AEC Savannah River Plant. Journal Qf Mammalogy, 1965, 46, 1-18. Grafen, A., & Sibly, R. A model of mate desertion. Animal Behaviour, 1978, 2..6.., 645-652. Grau, H. J. leucopus). Kin recognition in white footed deer-mice (Peromyscus Animal Behavior, 1982, N, 497-505. Hal I iday, T. R. Sexual selection and mate choice. In J. R. Krebs & N. B. Davies (Eds.) Behavioral ecology: An evolutionary approach. Oxford: Blackwel I Scientific Pub I ications, 1978.

PAGE 155

Halpin, Z. T. commentary. 148 Individual odors and individual recognition: Biology Qf Behaviour, 1980, 2, 233-248. Review and Halpin, Z. T., & Hoffman, M. Kin recognition and preference in the white-footed mouse (Peromyscus leucopus): Green beard or early socialization? Paper presented at meetings of the Animal Behavior Society, Knoxvi I le, Tennessee, 1981. Hamilton, W. D. The genetical theory of social behavior. I. Journal Qf Theoretical Blology, 1964, 2, 1-16. Ca) Hamilton, W. D. The genetlcal theory of social behavior. I I. Journal Qf Theoretical Biology. 1964, 2, 17-52. Cb) Hamilton, W. D., & Zuk, M. Heritable true fitness and bright birds: A role for parasites? Science, 1982, 2..18., 384-386. Ham i I ton, vi. J. The mamma Is Qf_ eastern United States. New York: Comstock Pub I ishing Co., 1943. Hansen, R. M. Communal I itters of Peromyscus maniculatus. Journal Qf_ Mamma I ogy, 1 957, :.lli, 523. Harris, V. T. An experimental study of habitat selection by prairie and forest races of the deermouse, Peromyscus maniculatus. Contributions from the Laboratory Qf_ Yertebrate Biology, University of Michigan, Ann Arbor, 1952, 2.Q., 1-53. Hayne, D. vi. Burrowing habits of Peromyscus pol jonotus. Journal _o_f Mammalogy, 1936, 11., 420-421. Healey, M. C. Aggression and self-regulation of populatlon size in deermice. Ecology. 1967, .4..8., 377-392. Heisler, I. L. Offspring quality and the polygyny threshold: A new model for the "sexy son" hypothesis. American Naturalist, 1981, ill, 316-327. Hil I, J. L. Peromyscus: Effect of early pairing on reproduction. Science, 1974, l..8.Q., 1042-1044.

PAGE 156

149 Hi I I, J. L. Space uti I ization of Peromyscus: Social and spatial factors. Animal Behaviour, 1977, 2..2., 373-389. Hinde, R. A. Psychology. Animal behavior: A. synthesis Qf ethology and comparative 2nd ed. New York: McGraw Hi I I, 1966. Hogan-Warburg, A. J. Social behavior of the ruff, Phi lomachus pugnax CL.). ~, 1966, 2, 109-225. Holbrook, S. J. Habitat relationships and coexistence of four sympatric species of peromyscus in northwestern New Mexico. Journal .Qf Mammalogy. 1978, .5.2., 18-26. Hoogland, J. L. Prairie dogs avoid extreme inbreeding. Science, 1982, ill, 1639-1641. Hooper, E. T. Classif i cation. In J. A. King (Ed.) Biology Q.f Peromyscus (Rodentia). Lawrence, Kansas: American Society of Mammalogists, 1968. Houtcooper, W. C. Rodent seed supply and burrows of Peromyscus in cultivated fields. Proceedings cl 1h.e. Indiana Academy Qf_ Science, 1972, fil, 384-389. Houtcooper, W. C. Food habits of rodents In a cultivated ecosystem. Journal Q.f Mammalogy, 1978, .5.2., 427-430. Howard, W. E. Dispersal, amount of inbreeding, and longevity in a local population of prairie deermice on the George Reserve, Southern Michigan. Contributions from the Laboratory of Vertebrate Biology, University of Michigan, Ann Arbor, 1949, .42, 1-52. Howard, W. E. Relation between low temperature and avai I able food to survival of smal I rodents. Journal Qf Mammalogy. 1951, 22., 300-312. Hrdy, S. Infanticide among animals: a review, classification, and examination of the imp I !cations for the reproductive strategies of females. Ethology .aru1 Sociobiology, 1979, l, 13-40. Huck, U. W. Pregnancy block in laboratory mice as a function of male social status. Journal of Reproduction .aru1. Ferti I ity. 1982, QQ., 181184.

PAGE 157

150 Huck, U. W., & Banks, E. M. Behavioral components of individual recognition In the collared lemming (Dlcrostonyx groenlandicus). Behavioral Ecology .a.rut Sociobiology, 1979, ~, 85-90. Huck, U. W., & Banks, E. M. The effects of cross-fostering on the behaviour of two species of North American lemmings, Dicrostonyx groenlandjcus and Lemmus trlmucronatus: I. olfactory preferences. Animal Behaviour, 1980, 2.8., 1046-1052. Huck, U. W., & Banks, E. M. Male dominance status, female choice and mating success in the brown lemming, Lemmus trimucronatus. Animal Behaviour, 1982, iQ, 665-675. Huck, U. W., Banks, E. M., & Wang, S. social status In the brown lemming. 1981, ll, 364-371. Olfactory discrimination of Behavioral and Neural Biology, Huck, U. W., Soltis, R. L., & Coopersmith, C. B. Infanticide in male laboratory mice: Effects of social status, prior sexual ~xperience, and basis for discrimination between related and unrelated young. Animal Behaviour, 1982, 1Q., 1158-1165. Jannett, F. J., Jr. Social dynamics of the montane vole, Microtus ochrogaster, as a paradigm. I.he Biologist, 1980, 62., 3-19. Jones, R. B., & Nowel I, N. W. Aversive and aggression promoting properties of urine from dominant and subordiante male mice. Animal Learning .a.rut Behavior, 1973, 1, 207-210. King, J. A. Ecological Psychology: An approach to motivation. Nebraska Symposium Motivation, 1970, 1.8., 1-33. Kleiman, D. G. Monogamy in mammals. Quarterly Review .of BioloQy, 1977, 22., 36-69. Kleiman, D. G., & Malcolm, J. R. The evolution of male parental investment in mammals. In D. J. Gubernlck & P. H. Klopfer (Eds.) Parental m ln mammals. New York: Plenum Pub I ishlng Corporation, 1981.

PAGE 158

151 Koenig, W. D., & Pitelka, F. A. Ecological factors and kin selection In the evolution of cooperative breeding in birds. In R. D. Alexander & D. W. Tinkle (Eds.) Natural selection and social behavior. New York: Chiron Press, 1981. Krames, L., Carr, W. J., & Bergman, B. A pheromone associated with social dominance among male rats. Psychonomjc Science, 1969, 16., 11-12. Krames, L., Costanzo, D. J., & Carr, W. J. Response of rats to odors from novel versus original sex partners. Proceedings of the 75th Annual Convention~ the American Psychological Association, 1967, 2., 117-118. Krebs, J. R., & Davies, N. B. An introduction to behavioural ecology. Sunderland, Massachusetts: Sinauer Associates, Inc., 1981. Kritzman, E. B. Ecological relationships of Peromyscus manjculatus and Perognathus parvus in eastern Washington. Journal of Mammalogy, 1974, 22., 172-188. Labov, J. B. Factors influencing infanticidal behavior in wi Id male house mice
PAGE 159

152 Landauer, M. R., Seidenberg, B. C., & Santos, A. V. Hormonal control of sexual preferences in male and female hamsters. Paper presented at the meeting of the Anlmal Behavior Society, Seattle, Washington, 1978. Lande, R. The maintenance of genetic variabi I ity by mutation in a polygenic character wi~h I inked loci. Genetics Research, 1976, 2.Q, 221-235. Lanier, D. L., Estep, D. 0., & Dewsbury, D. A. Role of prolonged copulatory behavior in faci I itating success in a competitive mating situation in laboratory rats. Journal .Qf Comparative .aru1 Physiological Psychology, 1979, 22, 781-792. Lawton, A. D., & Whitsett, J. M. Inhibition of sexual maturation by a urinary pheromone in male prarie deer mice. Hormones and Behavior, 1979, ll, 128-138. LeBoeuf, B. J. Male-male competition and reproductive success in Elephant Seals. American Zoologist, 1974, .1.A., 163-176. LeBoeuf, B. J., & Peterson, R. S. Social status and mating activity in Elephant Seals. Science, 1969, ill, 91-93. Lidicker, W. Z., Jr. The social biology of the California vole. Ib.e Biologist, 1980, Q.2., 46-55. Linduska, J. P. Winter rodent populations in field-shocked corn. Journal .of Wildlife Management, 1942, ~, 353-363. LI ewe I I yn, J. B. Season a I changes in the aggressive behavior of Peromyscus maniculatus inhabiting pinyon-junlper woodlands in western Nevada. Journal Qf Mamma!ogy, 1980, .fil., 341-345. Lombardi, J. R., & Whitsett, J. M. Effects of urine from conspecifics on sexual maturation in female prairie deer mice, Peromyscus maniculatus bajrdjj. Journal tl Mammafogy, 1980, fil, 766-768.

PAGE 160

153 Malnardi, D., Marsan, M., & Pasquali, A. Causation of sexual preferences of the house mouse. The behavior of mice reared by parents whose odor was artificially altered. Estratto dagl I Atti del la Societa Ital iana _gj_ Scienze Natural i .dtl Museo Civlco d!Storia Naturale Q_l_ Mi lane, 1965, l.QA., 325-338. Mallory, F. F., & Brooks, R. J. Infanticide and other reproductive strategies in the collared lemming, Dicrostonx groenlaodicus. Nature, 1978, ill, 144-146. Martel I, A. M., & Macaulay, A. L. Food habits of deer mice (Peromyscus maoiculatus) In Northern Ontario. Canadian Field-Naturalist. 1981, 22, 319-324. Martin, R. E. Species preferences of al lopatric and sympatric populations of silky pocket mice, genus Perognathus (Rodentia: Heteromyidae). American Midland Natural Jst, 1977, 2.8., 124-136. Maynard Smith, J. Ferti I ity, mating behavior, and sexual selection in Drosophila subobscura. Journal Qf_Genetics, 1956, 2A., 261-279. Maynard Smith, J. Evolution and the theory of games. American Scientist, 1976, QA, 41-45. Maynard Smith, J. Parental investment: A prospective analysis. Animal Behaviour, 1977, 22., 1-9. Maynard Smith, J. I.he evolution .of .s..ex... Cambridge: Cambridge University Press, 1978. Maynard Smith, J., & Price, G. R. The logic of animal confl let. Nature, 1973, 2..4.6., 15-18. Mayr, E. Populations, species, and evolution. Cambridge, MA: Harvard University Press, 1970. McDonald, D. L., & Forslund, L. G. The development of social preferences in the voles Mlcrotus montanus and Microtus canicaudus: effects of cross-fostering. Behavforal Biology. 1978, 22., 497-508. McGuire, M. R., & Getz, L. L. Incest taboo between sibling Microtus ochrogaster. Journal .of Mammalogy. 1981, 62., 213-215.

PAGE 161

fv'errett, R. B., & vlu, B. J. promyscus Maniculatus?) 154 On the quantification of promiscuity (or Evolution, 1975, 2.2., 575-578. ~~tzgar, L. H. Dispersion patterns in a Peromyscus population. Journal of Mammalogy. 1979, 60, 129-145. ~~tzgar, L. H. Dispersion and numbers in Peromyscus populations. American Midland Naturalist, 1980, .l.Ql, 26-31. Mihok, S. Behavioral structure and demogrephy of subarctic Clethrionomys gapperi and Peromyscus maniculatus. Canadian Journal of Zoology, 1979, 21., 1520-1535. Mi Iler, W. C. Ecological and ethological isolating mechanisms between Microtus pennsylvanicus and Microtus ochrogaster at Terre Haute, lndicna. American M idland Naturalist, 1969, .8..2., 140-148. lv'. i I Is, J. A. The inf I uence of age and pair-bond on the breeding biology of the red-bi I led gul I Larus novaehol landiae scapul inus. Journal of Animal Ecology. 1973, 42, 147-163. ~ brris, R. F. Population studies on some smal I forest manrnals in eastern Canada. Journal of Mammalogy, 1955, :iQ., 21-35. Murphy, M R. lntraspecific sexual preferences of female hamsters. Journal of Comparative .filLd. Physiological Psychology, 1977, 21, 1337-1346. / J' urphy, M R. Sexual preferences of male hamsters: Importance of preweaning and adult experience, vaginal secretion, and olfactory or vomeronasal sensation. Behavioral and Neural Biology. 1980, N, 323-340. Nakatsuru, K., & Kramer, D. L. Is sperm cheap? Limited male ferti I ity and female choice in the lemon tetra (Pices, ch~racidea). Science, 1982, 2.ln_, 753-754. Ni sbet, I C. T. common terns. Courtship-feeding, egg-size and breeding success in Nature, 1973, 241, 141-142. O'Donald, P. Possibi I ity of assertive mating in the Arctic skua. Nature, 1959, lfil, 1210-1211.

PAGE 162

155 O'Donnel I, Y., Blanchard, R. J., & Blanchard, D. C. Mouse aggression Increases after 24 hours of isolation or housing with females. Behavioral .aru1 Neural Blology, 1981, :iZ, 89-103. Orians, G. H. On the evolution of mating systems in birds and mammals. American Naturalist, 1969, ill, 589-603. Packer, C. anubus. Inter-troop transfer and inbreeding avoidance in~ Animal Behaviour, 1979, 21.., 1-36. Parker, G. A. Sexual selection and sexual conflict. In M. S. Blum & N. A. Blum (Eds.) Sexual selection E._'lQ_ reproductive competition In insects. New York: Academic Press, 1979. Partridge, L. Mate choice increases a component of offspring fitness in fruit flies. Nature, 1980, za}, 290-291. Poole, T. B., & Morgan, H. D. R. Social and territorial behaviour of laboratory mice (Mus musculus L.) in smal I complex areas. Animal Behaviour, 1976, 2..4_, 476-480. Pusey, A. E. Inbreeding avoidance in chimpanzees. Animal Behaviour, 1980, 2.8., 543-552. Rat Is, K. Mammals In which females are larger than males. Quarterly Review Qf Biology. 1976, 21, 245-276. Ral Is, K., Brugger, K., & Ballou, J. in smal I populations of ungulates. Inbreeding and juvenile mortality Science, 1979, 206, 1101-1103. Rand, A. L., & Host, P. Results of the Archbold expeditions. No. 45. Mammal notes from Highlands County, Florida. Bui letin of the American Museum of Natural History, 1942, all., 1-21. Randal I, J. A. Behavioral mechanisms of habitat segregation between sympatric species of Microtus: Habitat preference and interspecific dominance. Behavioral Ecology and Sociobiology, 1978, ~. 187-202. Rasmussen, D. I. Blood group polymorphism and inbreeding in natural populations of the deer mouse Peromyscus m.aniculatus. Evolution, 1964, 1.8., 219-229.

PAGE 163

156 Rasmussen, D. I. Biochemical polymorphisms and genetic structure in populations of Peromyscus. Symposium of the Zoological Society of London, 1970, 2.6., 335-349. Rathbun, G. 8. The social structure and ecology of elephant-shrews. Zeitschrift fur Tlerpsychology, Advances l!l ethology supplement, 1979, 2.Q., 1-80. Redfield, J. A., Krebs, C. J., & Taitt, M. J. Competition between Peromyscus maniculatus and Microtus townsendil in grasslands of coastal British Columbia. Journal Qf Animal Ecology, 1977, 46., 607-616. Reimar, J. D., & Petras, M. L. Breeding structure of the house mouse, M..u..s. musculus, in a population cage. Journal Qf Mammalogy. 1967, .46_, 88-99. Rice, L. Z. A study of food hoarding in freely growing laboratory populations of prairie deermice. Unpubl ishea masters thesis, College of Wil I lam and Mary, 1972. Ruddy, L. L. Discrimination among colony mates' anogenital odors by guinea pigs(~ porcel lus). Journal of Comparative and Physiological Psychology, 1980, 24_, 767-774. Sadleir, R. M. F. S. The relationship between agonlstlc behavior and population changes in the deermouse Peromyscus manlcu!atus (Wagner). Journal .Qf Animal Ecology, 1965, ll, 331-352. Schwagmeyer, P. L. The Bruce effect: An evaluation of male/female advantages. American Natural 1st, 1979, ll..4., 932-938. Scott, J. P. Agonlstic behavior of mice and rats: A review. American Zoologist, 1966, ~, 683-701. Scott, J. P., & Frederickson, E. The causes of fighting in mice and rats. Physiological Zoology, 1951, 2A., 273-309. Selander, R. K. Behavior and genetic variation in natural populations. American Zoologist, 1970, l.Q., 53-66.

PAGE 164

157 Selander, R. K., Smith, M. H., Suh, Y. Y., Johnson, W. E. & Gentry, J. B. IV. Biochemical Polymorphism and systematics in the genus Peromyscus. I. Variation in the old-field mouse. Studies in genetics VI. University of Texas Pub I ication 7103, 1971. Seligman, M. E. P. On the generality of the laws of learning. Psychological Review. 1970, ll, 406-418. Shields, W. M. Inbreeding and the paradox of sex: A resolution? Evolutionary Theory. 1982, 2, 245-279. Siegel, S. Nonparametric statistics for the behavioral sciences. New York: McGraw-Hi I I Book Company, Inc., 1956. Simon, N. G. The genetics of intermale aggressive behavior in mice: Recent research and alternate strategies. Neuroscience~ Biobehavioral Reviews, 1979, ~. 97-106. Smith, M. H. The evolutionary significance 2f. certain behavioral, physiological, and morphological adaptations of the old-field mouse. Peromyscus pol ionotus (Doctoral dissertation, University of Florida, 1966). Dissertation Abstracts, 1967, 21_, 4692B-4693B. (University Microfilms No. 67-372) Smith, M. H. Mating behavior of Peromyscus pol ionotus. Quarterly Journal Qf_ the Florida Academy of_ Sciences, 1967, iQ., 230-240. Smith, M. H. Dispersal of the old-field mouse, Peromyscus pol lonotus. Bui letin Qi_ the Georgia Academy Qf_ Science. 1968, 2.6., 45-51. Smith, M. H. Food as a I imiting factor in the population ecology of Peromyscus polionotus. Annales Zoologlci Fennici, 1971, a, 109-112. Smith, M. H., & Blessing, R. W. Trap response and food avai labi I ity. Journal Qf Mammalogy, 1969, 2.Q., 368-369. Smith, M. H., Carmon, J. L., & Gentry, J. B. Pelage color polymorphism In Peromyscus pol ionotus. Journaf_Qf Mammafogy, 1972, 22, 824-833.

PAGE 165

158 Smith, M. H., & Criss, W. E. Effects of social behavior, sex and ambient temperature on the endogenous diet body temperature cycle of the old-field mouse, Peromyscus pol ionotus. Physiological Zoology, 1 967, Q..Q., 31-39. Smith, M H., Garten, C. T., Jr., & Ramsey, P. R. Genie heterozygosity and population dynamics in smal I marrrnals. In C. L. M arkert (Ed.) lsozymes .l..'l.;_ Genetics Qilll Evolution. New York: Academic Press, 1975. Smith, M. H., & ~tGinnis, J. T. Relationships of latitude, altitude, and body size to I itter size and mean annual production of offspring in Peromyscus. Researches QO. Population Ecology, 1968, lQ., 11 5-126. Stacey, P. B. Female promiscuity and male reproductive success in social birds and marrmals. American Natural jst, 1982, 12.Q., 51-64. Stickel, L. F. Home range and travels. In J. A. King (Ed.) Biology of Peromyscus (Rodentia). Lawrence, Kansas: American Society of Mammalogists, 1968. Sugiyama, Y. On the social change of Hanuman langurs (Presbytis entel !us) in their natural conditions. Primates, 1965, ~, 381-418. Taitt, M J. The effect of extra food on smal I rodent populations: I. deermice (P e romyscus manicu!atus). Journal Qf Animal Ecology, 1981, .2.Q., 111-1 24. Terman, C. R. Some dynamics of spatial distribution within semi-natural populations of prairie deermice. Ecology. 1961, 12., 288-302. Terman, C. R. Population dynamics. In J. A. King (Ed.) Biology Qf Peromyscus
PAGE 166

159 Thiessen, D. D., & Maxwel I, K. 0. A glass rodent enclosure: Gerbi I city. Behavior Research Methods & Instrumentation, 1979, ll, 535-537. Thomas, J. A., & Birney, E. C. Parental care and mating system of the prarie vole, Mlcrotus ochrogaster. Behavioral Ecology and Sociobiology, 1979, ~, 171-186. Thorpe, W. H. BJ..o;1 London: Cambridge University Press, 1961. Tinbergen, N. K. study .Q.f Instinct. Oxford: Oxford University Press, 1951. Trivers, R. L. Parental investment and sexual selection. In B. Campbel I (Ed.) Sexual selection and the descent of man, 1871-1971. Chicago: Al dine, 1972. -----Trivers, R. L. Sexual selection a 1d resource-accruing abi I ities In Aoolis garmani. Evolution, 1976, N, 253-269. Vaughan, T. A. Mammalogy, Philadelphia: W. B. Saunders Company, 1978. Verner, J. Evolution of polygamy In the long-bl I led marsh wren. Evolution, 1964, 18., 252-261. Verner, J., & Wll Ison, M. F. The influence of habitats on mating systems of North American passerine birds. Ecology, 1966, ll, 143-147. Vestal, B. M., & Hel lack, J. J. Comparison of neighbor recognition In two species of deer mice (Peromyscus). Journal of Mammalog~, 1978, ~, 339-346. Wade, M. J. Sexual selection and variance In reproductive success. American Naturalist, 1979, ill, 742-746. Ward, S. E., Baumgardner, D. J., & Dewsbury, D. A. Experimental determinants of female mating preference In Mlcrotus ochrogaster and M... montanus. Paper presented at meetings of the Animal Behavior Society, Knoxvi I le, Tennessee, June, 1981.

PAGE 167

160 Weatherhead, P. J., & Robertson, R. J. Offspring qua I ity and the po I ygyny th res ho Id: "the sexy son hypothesis!' American Natura Ii st, 1979, ill, 201-208. Webster, D. G., Sawrey, D. K., Williams, D. C., & Dewsbury, D. A. Apparatus for assessment of rodent social preference. Paper presented at the meetings of the Animal Behavior Society, Duluth, Minnesota, 1982. Webster, D. G., Wil Iiams, M. H., & Dewsbury, D. A. Female regulation and choice in the copulatory behavior of Montane voles
PAGE 168

161 \Vi 11 iams, R. G., Gol ley, F. B., & Carmon, J. L. Reproductive performance of a laboratory colony of!:..... pol ionotus. American M idland Naturalist, 1965, 73, 101-110. \ Ji Ison, E. 0. Sociobiology: The H.fili Synthesis. Cambridge: Harvard University Press, 1975. \ 1 Hlson, J. R., K uehn, R. E., & Beach, F. A. r : odification in the sexuel behavior of male rats produced by changing the stimulus female. Journal of Comparative _gllij Physiological Psychology, 1963, 2.Q., 636-644. Wittenberger, J. F. The evolution of mating systems in birds and maITTTials. In P. f 1 arier & J. Vandenberg (Eds.) Handbook Qi behavioral neurobiology. Vol. 3. Social behavior and communication, New York: Plenum, 1979. W ittenber g er, J. F. Animal social behavior. Boston: Duxbury Press, 1981 vlittenber g er, J. F., & Ti Ison, R. L. The evolution of monogamy: Hypotheses and evid e nce. Annual Review of Ecology QQ.d. Systemics, 1980, U, 197-232. Zahavi, A. M ate selection--A selection for a handicap. Journal Qf Theoretical B iology, 1975, 22, 205-214. Zucker, I., & \ J ade, G. Sexua I preferences of ma I e rats. Journa I Qf Comparative and Physiological Psycholooy. 1968, QQ, 816-819.

PAGE 169

BIOGRAPHICAL SKETQ-l was a member of the "baby boom," born to George E. and M ary L. \ Jeb ster on May 5, 1 948. I started my I if e in Oshkosh, Wisconsin. Three moves later the family was settled in my parents present home in Rothschild, ~/isconsin. I completed high school in neighboring Schofield a7 D. C. Everest (hane of the "Evergreens") in 1966, and continued my education for another two years at the Marathon Campus of the University of Wisconsin, in ~/ausau, \'/isconsin. Toward the end of 1 968 I met Caro I e and f o I I owed her south to New Orleans, where we were married in July of 1969. In August of 1969 became a member of the U. S. Air Force and served four years as an oral surgery technician at Keesler A.F.B., Biloxi, ~ississippi. Our daughter, Daniel le, was born in 1972 just prior to our leaving the service and rejoining the student population. I completed the requirements for my B.S. at the University of Wisconsin in Madison, \ lisconsin, in 1976, and we headed back south to the University of Florida where I completed the requirements for the ~1.S. in 1979. 162

PAGE 170

I certify that I have read this study and that In my opinion It conforms to acceptable standards of scholarly presentation and is fully adequate, In scope and qua I lty, as a dissertation for the de~ree of Doctor of Philosophy. Dr. Donald A. Dewsbury, Chai Professor of Psychology I certify that I have read this study and that In my opinion It conforms to acceptable standards of scholarly presentation and is fully adequate, In scope and qua I lty, as a dissertation for the degree of Doctor of Philosophy. Dr. Merle E. Meyer Professor of Psychology I certify that I have read this study and that In my opinion It conforms to acceptable standards of scholarly presentation and is fully adequate, In scope and qua I ity, as a dissertation for the degree of Doctor of Philosophy. L-A I ~ \. ; . ( / ./ / 1 1/ ,, )1 '-. J 7 L / / Dr. Wilse B. W~bb Graduate Research Professor of Psychology

PAGE 171

I certify that I have read this study and that In my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and qua I lty, as a dissertation for the degree of Doctor of Philosophy. Dr. Carol Van Hartesveldt Associate Professor of Psychology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, ~s a dissertation for the degree of Doctor of Philosophy. Dr. H. Jane Brockmann Associate Professor of Zoology This dissertation was submitted to the Graduate Faculty of the Department of Psychology in the College of Liberal Arts and Sciences and to the Graduate Counci I, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. Apr 11 1983 Dean for Graduate Studies and Research

PAGE 172

UNIVERSITY O F FLORIDA II I II IIIIII Ill Ill lllll lllll II IIIIII III I II IIIIII Ill lllll llll Ill I I 3 1262 08553 5945