Analysis of the genetic components of life history parameters using laboratory reared Simocephalus (Cladocera)

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Title:
Analysis of the genetic components of life history parameters using laboratory reared Simocephalus (Cladocera)
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xi, 125 leaves : ill. ; 28 cm.
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English
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White, Charles Pomeroy, 1951-
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Cladocera   ( lcsh )
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theses   ( marcgt )
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Thesis:
Thesis (Ph. D.)--University of Florida, 1981.
Bibliography:
Includes bibliographical references (leaves 122-124).
Statement of Responsibility:
by Charles Pomeroy White.
General Note:
Typescript.
General Note:
Vita.

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University of Florida
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ANALYSIS OF THE GENETIC COMPONENTS OF
LIFE HISTORY PARAMETERS USING LABORATORY
REARED SIMOCEPHALUS (CLADOCERA)













BY
CHARLES POMEROY WHITE


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


1981















ACKNOWLEDGEMENTS


I thank Carmine Lanciani for the ideas and encouragement he

has provided on countless occasions. I also thank F. G. Nordlie,

J.T. Giesel, J.S. Davis, D. Valentine, and R.A. Alford for their

help. I give special recognition to the support of Belvidere

and Shrub Hill.
















TABLE OF CONTENTS



SECTION PAGE



ACKNOWLEDGEMENTS ......................................... ii

LIST OF TABLES ........................................... iv

LIST OF FIGURES .......................................... ix

ABSTRACT ................................................... x

INTRODUCTION ............................................... 1

METHODS .................................................. 5

COLLECTION SITES ......................................... 11

RESULTS .................................................. 17

DISCUSSION ............................................... 26

LITERATURE CITED ......................................... 122

BIOGRAPHICAL SKETCH ..................................... 125















LIST OF TABLES


TABLE PAGE

1 Survival rate of 3 species of Simocephalus 46
cladocerans to age 14 days.
2 Intrinsic rate of natural increase (rm) for 47
3 species of Simocephalus.
3A Comparison of size-specific fecundity of field 48
collected and laboratory-reared S. serrulatus
from the River Styx Pond.
3B Comparison of size-specific fecundity of field- 49
collected and laboratory-reared S. serrulatus
from Stock Pond.
3C Comparison of size-specific fecundity of field- 50
collected and laboratory-reared S. serrulatus
from River Styx Bridge.
3D Comparison of size-specific fecundity of field- 51
collected and laboratory-reared S. vetulus
from Pine Pond.
3E Comparison of size-specific fecundity of field- 52
collected and laboratory-reared S. vetulus
from Lake Alice.
3F Comparison of size-specific fecundity of field- 53
collected and laboratory-reared S. vetulus
from Psychology Pond.
3G Comparison of size-specific fecundity of field- 54
collected and laboratory-reared S. exspinosus
from Archer.
3H Comparison of size-specific fecundity of field- 55
collected and laboratory-reared S. exspinosus
from Pine Pond.
31 Comparison of size-specific fecundity of field- 56
collected and laboratory-reared S. exspinosus
from Puddle.
4 Body length at age 14 days and rm values for 57
January and April cohorts of the same clones
of Simocephalus.








TABLE PAGE

5 rm values and analysis of variance of cloned 58
Archer hearings. Number of generations.
6 Size at first reproduction of cloned Archer 59
hearings.

7 Age at first reproduction of cloned Archer 60
hearings.
8 Size of newborn of cloned Archer hearings. 61

9 Death rates (number of dead/number of days 62
lived) of cloned Archer hearings through day
14.
10 Growth rates of cloned Archer hearings. 63
11A m(x) of cloned Archer hearings; means. 64
11B m(x) of cloned Archer hearings; analysis of 65
variance.

12A Age-specific size of cloned Archer hearings; 66
means in mm.
12B Age-specific size of cloned Archer hearings; 67
analysis of variance.
13 Size of eggs as a function of age of parents. 68

14A Size of young born to parents of various ages 69
in S. exspinosus collected from Mt. Vernon Pond.
14B Size of young born to parents of various ages 70
in S. vetulus collected from Austin Carey Pond.
14C Size of young born to parents of various ages 71
in S. vetulus collected from Biven's Arm.
14D Size of young born to parents of various ages 72
in S. serrulatus collected from Biven's Arm.
14E Size of young born to parents of various ages 73
in S. serrutatus collected from River Styx
Pond.
15 Relationship between food level and r of 3 74
different lines of S. exspinosus.
A. r values of the S. exspinosus food
hearings.
B. Characteristics of plots of r-logl0
food level.
C. Analysis of covariance of lines in "B".









PAGE


16A Size-specific fecundity of 3 lines of S. exspi- 76
nosus at a food level of 1,000,000 cells/ml.
16B Size-specific fecundity of 3 lines of S. exspi- 77
nosus at a food level of 500,000 cells/ml.
16C Size-specific fecundity of 3 lines of S. exspi- 78
nosus at a food level of 250,000 cells/ml.
16D Size-specific fecundity of 3 lines of S. exspi- 79
nosus at a food level of 50,000 cells/ml.
16E Size-specific fecundity of 3 lines of S. exspi- 80
nosus at a food level of 5,000 cells/ml.
16F Size-specific fecundity of 3 lines of S. exspi- 81
nosus at a food level of 0 cells/ml.
17A Age-specific fecundity of 3 lines of S. exspi- 82
nosus at a food level of 1,000,000 cells/ml.
17B Age-specific fecundity of 3 lines of S. exspi- 83
nosus at a food level of 500,000 cells/ml.
17C Age-specific fecundity of 3 lines of S. exspi- 84
nosus at a food level of 250,000 cells/ml.
17D Age-specific fecundity of 3 lines of S. exspi- 85
nosus at a food level of 50,000 cells/ml.
17E Age-specific fecundity of 3 lines of S. exspi- 86
nosus at a food level of 5,000 cells/ml.
17F Age-specific fecundity of 3 lines of S. exspi- 87
nosus at a food level of 0 cells/ml.
18A Age-specific size of 3 lines of S. exspinosus 88
at a food level of 1,000,000 cells/ml.
18B Age-specific size of 3 lines of S. exspinosus 89
at a food level of 500,000 cells/ml.
18C Age-specific size of 3 lines of S. exspinosus 90
at a food level of 250,000 cells/ml.
18D Age-specific size of 3 lines of S. exspinosus 91
at a food level of 50,000 cells/ml.
18E Age-specific size of 3 lines of S. exspinosus 92
at a food level of 5,000 cells/ml.
18F Age-specific size of 3 lines of S. exspinosus 93
at a food level of 0 cells/ml.


TABLE








TABLE PAGE

19 Relationship between food level and size at first 94
reproduction of 3 lines of S. exspinosus.
20 Relationship between food level and age of first 95
reproduction of 3 lines of S. exspinosus.
21 A. Relationship between food level and growth 96
rates of 3 lines of S. exspinosus.
B. Growth rates of cloned Archer hearings of
S. exspinosus.
C. Growth rates of 3 species of Simocephalus.
D. Growth rates of S. exspinosus from Archer and
Pine Pond sites.
22 Relationship between food level and death rate 97
(number dead/number of days lived) of 3 lines of
S. exspinosus.
23 Comparison of life history features of Pine Pond 98
and Archer S. exspinosus populations.
24 Age-specific size of Archer and Pine S. exspinosus 99
populations. P < .05 at all ages.
25 Size-specific fecundity of Pine and Archer S. exspi- 100
nosus populations. P > .05 at all sizes.
26 Age-specific fecundity of Pine and Archer S. exspi- 101
nosus populations.
27 A. Mean pigmentation ranks for 3 species of Simo- 102
'ephalus from 8 collection sites.
B. Analysis of variance and Kruskal-Wallis k-sample
tests of pigmentation rank means.
28 Relationship between eyespot size and body length 103
of S. exspinosus not exposed to visually-oriented
predation (Archer) and exposed to visually-oriented
predation (Pine, Puddle, and Mt. Vernon Ponds).
29 Age-specific size of all species. 104
30 Size-specific fecundity of all species. 106
31 Age-specific fecundity of all species. 108
32 rm values of all species. 110
33 Age at first reproduction of all species. 111
34 Size at first reproduction of all species. 112
35 Death rates (number of dead/number of days lived) 113
of Simocephalus reared to age 14 days.


vii








TABLE PAGE

36A Age-specific size of S. exspinosus from 6 sites. 114
36B Age-specific size of S. exspinosus from 6 sites; 115
analysis of variance.
37A Age-specific fecundity of S. exspinosus from 6 116
sites.
37B Age-specific fecundity of S. exspinosus from 6 117
sites; analysis of variance.

38 Size at first reproduction of S. exspinosus from 118
6 sites.

39 Age at first reproduction of S. exspinosus from 119
6 sites.

40A Size-specific fecundity of S. exspinosus from 6 120
sites.
40B Size-specific fecundity of S. exspinosus from 6 121
sites; analysis of variance.


viii
















LIST OF FIGURES


Relationship between food level
and r of 3 different lines of
S. exspinosus............................ ...... Page

Age-specific size of all species............... Page

Size-specific fecundity of all
species......................................... Page

Age-specific fecundity of all
species....................................... Page


Figure 1.


Figure

Figure


Figure 4.


75

105


107


109














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




ANALYSIS OF THE GENETIC COMPONENT OF LIFE
HISTORY PARAMETERS USING LABORATORY-REARED
SIMOCEPHALUS (CLADOCERA)

By

Charles Pomeroy White

March 1981


Chairman: Carmine A. Lanciani
Major Department: Zoology

Laboratory hearings of field-collected, cloned Simocephalus

exspinosus provided data that do not support the r- and K-selection

model. A shift from r-selected to K-selected characters was not

observed in a temporary pond population initially subjected primar-

ily to density-independent mortality factors and later, as the pond

decreased in size, to increasingly greater density-dependent

mortality factors. The life history features of animals sampled

throughout this period remained nearly constant. These results are

consistent with data from laboratory hearings that indicated that

some clones were of superior fitness over all food concentrations

tested.

Simocephalus exspinosus, S. vetulus, and S. serrulatus populations

appear to respond to nonvisually-oriented predation by increased








age-specific size, increased age-specific fecundity, and increased

intrinsic rates of natural increase (rm) and respond to visually-

oriented predation by decreased size at first reproduction, de-

creased age-specific size, decreased rm values, greater body pigmen-

tation, and smaller eyespot-body size ratios.

Interspecific differences in life history parameters and habitat

preferences were observed among the three species by means of field

collections and laboratory hearings. SimocephaZus exspinosus, which

inhabits primarily temporary ponds, has the greatest age-specific

size, smallest size-specific fecundity, and largest size at first

reproduction. Simocephalus vetulus, which inhabits both temporary

and permanent ponds, has the smallest age-specific size, largest

size-specific fecundity, and smallest size at first reproduction.

Simocephalus serrulatus, which inhabits primarily permanent lakes,

has the lowest age at first reproduction and showed no evidence of

males and ephippial females, which were occasionally seen in the

other species.

















INTRODUCTION



Simocephalus are large (less than 3.5mm) cladocerans of the

family Daphnidae that are abundant in many bodies of water in

north central Florida during the winter and early spring. Three

species, S. exspinosus Koch, S. vetulus O.F.M. and S. serrulatus

Koch, can be found in a wide variety of habitats ranging from small

bathtub-size puddles to the large natural lakes of the area. Unlike

most of the Daphnidae commonly studied, they are benthic, i.e. they

are associated with substrates such as vegetation and sediment

surfaces. These cladocerans are quite useful in ecological studies

for several reasons. Simocephalus are easy to collect in large

numbers with a minimum of equipment. The variety of habitats they

inhabit allows researchers to collect from allopatric populations

of the same species that have been subjected to different selective

pressures. Each species can be collected in sites containing only

one species as well as sites containing two species, thus allowing

both interspecific and intraspecific comparisons. Simocephalus

are large enough to be seen with the unaided eye, greatly simpli-

fying their handling, but are small enough to be reared in large

quantities in a small space. Reproducing primarily by mitotic

parthenogenesis, they can be cloned in the laboratory, allowing









the maintenance of lines for long periods and the accurate measure-

ment of the phenotypic variability of a genotype.

Simocephalus were used to examine several ecological questions.

Some assumptions of the r- and K-selection model (MacArthur and

Wilson 1967) were tested using S. exspinosus from several different

habitats. The model predicts that populations subjected to predom-

inantly density-independent (D.I.) mortality factors would have differ-

ent life history tactics than those subjected to predominantly density-

dependent (D.D.) mortality factors. Individuals in populations under

D.I. control should be r-selected, producing a maximum number of off-

spring without regard to competitive ability. Populations under D.D.

control would contain K-selected individuals that would produce more

competitive but fewer young. A continuum exists between extreme r-

selection and extreme K-selection with numerous correlates associated

with each end (Pianka 1970). As the importance of D.D. factors in-

crease relative to D.I. factors, K-selected characters should be-

come more favored by natural selection than r-selected characters.

A tradeoff should occur between the two ends of the continuum for

the effects of r-and K-selection are opposite (Gadgil and Bossert

1970). An organism adapted to r-selection should show reduced fit-

ness under K-selected conditions and vice versa.

Evidence for this predicted tradeoff was sought in two ways.

Simocephalus exspinosus from one temporary pond were cloned and

reared under controlled conditions. Individuals collected soon

after the pond filled would most likely have been under D.I.

control and thus should show r-selected characteristics: high rm









values, small age-specific size, high age-specific fecundity,

high size-specific fecundity, small age at first reproduction,

small size at first reproduction, and high relative growth rates.

As the pond dried and the population increased toward the carrying

capacity, D.D. factors would most likely have become more important,

favoring the individuals that possessed relatively K-selected

characteristics: low rm values, large age-specific size, small

age-specific fecundity, low size-specific fecundity, large age

at first reproduction, large size at first reproduction, and low

relative growth rates. Measurements of these parameters were

taken from animals collected on six dates from January 15 until

March 27, enough time for approximately 10 generations of S.

exspinosus (Table 5), to see if the expected tradeoff occurred.

The relationships between age of parents and size of their eggs

and young were examined to determine whether the manipulation of

egg and young size could be used for regulating reproduction at

various ages.

For further evidence, a food experiment was conducted to deter-

mine whether clones with high rates of increase (r) at high food

levels had lower r values at low food levels than clones with low r

values at high food levels. Three clones were reared under six

different food concentrations to see whether this tradeoff would

occur. Since food supply per individual in natural populations

would most likely be inversely proportional to population density,

varying food levels should allow indirect examination of the

effects of population density on r values.









Another subject of ecological concern is the reaction of prey

species to visual and nonvisual predation. Numerous investigators

have reported increased predator avoidance by the evolution of

changes in size, body shape, and pigmentation by cladocerans and

other members of the plankton (Confer and Blades 1975; Dodson 1970,

1972, 1974a,b; Hairston 1979a,b; Hutchinson 1967; Kerfoot 1974,

1975, 1977a,b, 1978; Kerfoot and Peterson 1980; Mellors 1975;

O'Brien and Vinyard 1978; O'Brien etal. 1979; Sprules 1972; Werner

and Hall 1974; Zaret 1972a,b; Zaret and Kerfoot 1975). The tactics

used by the more benthic cladocerans, such as Simocephalus, have not

received the same attention. Intraspecific comparisons of life

history traits, morphology, and pigmentation of two populations of

S. exspinosus, one subjected to very little predation of any kind

and the other subjected to heavy fish predation, are made from

both laboratory-reared and field-collected animals. Laboratory

observations confirm that two species of fish, Gambusia affinis

and Heterandria formosa, commonly found in the same sites as

Simocephalus, readily ingest Simocephalus. In addition, comparisons

of laboratory hearings and field collections of animals from a variety

of habitats provide insight into the interspecific and intraspecific

trends induced by various types of predation.

The third major part of this investigation is a comparison of

some of the ecological characteristics of the three species. The key

identifying characters, the habitat preferences, and differences in

growth rates and life history strategies are examined. Life history

traits were determined through laboratory hearings while the key

characters were examined using field-collected specimens.
















METHODS


A consistent rearing method that can be duplicated over long

periods and that allows uniform growth, survival, and reproduction

is needed to study the life history features of cladocerans. Such

a method used while examining the life history tactics of Simocephalus

populations at different times in the same temporary pond has five

major components (White 1981).

Food--Unialgal cultures, of the unicellular green alga Stichococcus

bacillaris Nag obtained from a contaminated flask of culture medium

provided a consistent and easily quantifiable source of food that

met the nutritional requirements of the cladocerans. Algal cultures

were grown under cool white fluorescent lights in 2 1 flasks

containing Bold's Basal "3N" growth medium (Bold 1967). The flasks

were plugged with cotton through which glass tubes extending into

the liquid were inserted. Filtered air was pumped through these

tubes to aerate and agitate the cultures.

Simocephalus were provided with algal cells at a concentration

of 500,000 cells/ml, which apparently provided a superabundant food

supply. Hutchinson (1967) reported that S. vetuZus reaches a

plateau of feeding efficiency at food concentrations between

250,000 and 500,000 cells/ml. Food was prepared each day by count-

ing the individual cells in a known volume of algal stock with a

hemocytometer and diluting this stock to the proper concentration.









Water--Water was conditioned by passage through two 110 1

aquaria. Tap water was introduced into the first tank, which con-

tained numerous small fish, a large population of snails, and a

dense growth of Vallisneria. A fluorescent light in the hood was

kept on continuously, and the 568 1/hr motor driven filter was

cleaned every week. Water was siphoned from this tank to another

unilluminated one that contained a few fish and snails but no

plants. This aquarium had both an undergravel filter and a 568

1/hr motor driven filter. Water from the second aquarium was placed

in 2 flasks and autoclaved for 15 min at 1210 C under 1,520 mmHg.

Taub and Dollar (1968) reported that autoclaved culture water

boosted survival and reproduction in Daphnia pulex. After cooling

overnight, the water was mixed with the algal stock and used.

Temperature--Experimental cultures were reared at 270 C. Other

cultures raised at 200 C and 300 C indicate that this setting is

within the tolerance range of Simocephalus.

Light--An illumination schedule of 12 hr light and 12 hr dark

was maintained. Animals reared under 24 hr of light did well, while

those raised in complete darkness usually died, indicating that

some light is important.

Rearing tests--Collections were made in the field with a white

pan and an eye dropper. The pan was dipped into the water among

vegetation or slightly above the bottom and then placed on a level

surface. Simocephalus were removed from the pan individually with

an expanded eye dropper and placed into a vial for transport to

the laboratory. Each field-collected animal was isolated and sub-

jected to the rearing conditions. These individuals were allowed to









reproduce at least three times in the laboratory, after which

young were isolated and the field-collected individuals discarded.

These young were allowed to reproduce at least three times,

after which young were again isolated and the parents discarded.

These young were used in the experiments. Each individual was

kept in its own container, a 220 ml capacity plastic cup containing

60 ml of the diluted algal culture. These cups were kept on white

trays in an environmental chamber. Each day the contents of the

cup were poured into an illuminated 76 mm glass culture dish,

the cladoceran was transferred with an expanded eye dropper to a

duplicate cup containing fresh food, and the newborn were collected

by pouring them into a 74 micron sieve. Offspring from clones of

10 siblings were collected on the sieve, washed into a plastic pill

vial, killed with 10% formalin, and counted at 12 power with a

dissecting microscope. Body lengths were measured at 24 power

using a dissecting microscope with a measuring eyepeice. Algal

build-up was removed from the sides and bottom of the culture cups

each week.

Evaluation of Method-- Three questions must be considered

before confidence can be placed in the technique. Does it allow

high rates of survival and reproduction? The survival rates to

age 14 days of clones of S. exspinosus, S. vetulus, and S. serrul-

atus are in Table 1, and the mean intrinsic rate of natural in-

crease, rm, for the same clones are in Table 2. These tables

indicate that the method allows high rates of survival and repro-

duction. In addition, comparisons between field-collected and

laboratory-reared specimens show that size-specific fecundity was









consistently greater in the laboratory-reared animals (Table 3A-I).

Does the method allow consistency over a long period of time?

In Table 4, body lengths at age 14 days and rm values of specimens

from January and April cohorts of the same clones indicate that

consistency is maintained. Does it allow consistency between parents

and offspring? For 10 parent-offspring pairs, a paired comparison

"t" test showed no difference between the total number of young

produced by age 14 days (0.4 >p >0.2) or between the body length

at age 14 days (0.9>p>0.5).

The food experiment used the same method with some modifications.

Food concentrations of 1,000,000, 500,000, 250,000, 50,000, 5,000,

and 0 cells/ml were used. The 1,000,000 cells/ml concentration was

made first each day by the use of the hemocytometer. Other food

levels were achieved by dilution of the concentration. The auto-

claved aquarium water was filtered through a 0.47 micron millipore

filter to assure that the algal cells, added later, were the main

source of food. Three clones were used for the study, each chosen

for its rm value from a previous rearing. Eight members of each

clone were reared at each food level. All individuals were measured

each day, and the young from each animal were counted as they were

removed from the illuminated culture dish with an eye dropper.

The hearings used in the comparison of the three species also

employed the same techniques with slight alterations. Each field-

collected specimen was represented by only one animal in the lab-

oratory hearings. This provided for a measure of variability in

the population but not in the individual genotype. All animals









were measured each day, and the young were counted as they were removed

from the culture dish with an eye dropper.

To determine the relationship between the size of the young and the

age of the parent, newborn from adults of known ages were measured under

a 24 power dissecting microscope. All the young of the first brood were

measured, and 5 young were measured at random from later broods. If

shed skins were evident, indicating that the young had molted, animals

of that brood were not measured. For this determination, several indiv-

iduals were reared for as long as 33 days instead of the usual 14 days.

To see if the size of the eggs changed with the age of the parent,

specimens from 4 clones were reared using the standard method for as

long as 25 days. Individuals from the clones were killed and stripped

of eggs when the eggs were seen to be at the correct stage of develop-

ment. All eggs unbroken during removal were measured along the long

axis under a 100 power dissecting microscope.

To determine growth rates of each species of Simocephalus, knowledge

of the relationship between body length and weight was required. Labor-

atory-reared animals were measured under a 24 power dissecting micro-

scope, dried in a 600 C drying oven for 2 days, and weighed on a Cahn G-2

electric balance to yield equations that would predict the dry weight

from body length of the living animals. Four equations were used: (S.

vetulu.)logl0X= 2.90 logl0Y 6.08; (S. serrulatus)log10X= 3.07 logl0Y -

6.35; (Pine Pond S.exspinosus) logl0X= 3.60 logl0Y 7.18; and (other S.

exspinosus) logl0X= 4.65 logl0Y 9.04; where X is the dry weight in

milligrams, and Y is the length in measuring eyepiece units (0.0378 mm).

Some data were obtained from field-collected organisms. These

animals were transported live to the laboratory where they were killed








in dilute alcohol and immediately examined under a microscope. The length,

the number of eggs, presence of spinules on the vertex, shape of the

ocellus, size of the eyespot along the longest axis, and the pattern of

spination on the postabdominal claw were recorded for most individuals.

Some animals were measured only for length, number of eggs, and degree

of pigmentation on the shell. Pigmentation was measured using a rating

system of from 1-5.

1= no pigmentation in the shell

2= shell with a few scattered patches

3= shell with a distinct pattern of pigmentation

4= pigmentation over most of the shell

5= pigmentation over the entire shell

The red tinge common in S. exspinosus from highly stained water was not

considered to be pigmentation in the shell.

The bulk of the data was analyzed using programs of the Statistical

Analysis System (S.A.S. 1979) and the Northeast Regional Data Center

computer in Gainesville, Florida. Analyses of variance were performed

using the general linear model procedure. The Duncan Multiple Range

test was used to determine the location of significant differences among

3 or more means. Labels of means not significantly different from each

other at the .05 level are joined by an underline in the tables. For

the food experiment, differences among the slopes and y intercepts of the

3 lines formed by plotting r against log10 food concentration were exam-

ined using analysis of covariance. Pigmentation rankings were subjected

to the nonparametric one-way analysis procedure that included parametric

one-way analysis of variance and Kruskel-Wallis K-sample tests.

A paired-observation t-test contained on a Monroe 344 calculator

was used to analyze eyespot size data.









Growth data fit the logistics growth model (Ricklefs 1967),

allowing relative growth rates to be calculated using the methods

of Crossner (1977).

Values of r and rm were calculated on aTektronix 31 programmable

calculator using the equation 1= E e-rm x x mx.

Collection Sites--The Archer site is found at the southeast

corner of Old Archer Road and S.W. 23rd Street in Gainesville, Florida.

It is an unshaded, unstained drainage ditch no greater than 1.5m wide

and no greater than 0.5m deep. The ditch floods to a length of about

100m during a heavy rain but holds water for only about 15m of its

length for any extended period. One end of the ditch accepts water

runoff from a University of Florida livestock rearing complex, and

the other end empties into a drainage culvert. The ditch experiences

unidirectional flow during and for a short time after a heavy rain.

The bottom of the culvert is above the bottom of the ditch, allowing

a puddle of standing water to remain. The size and depth of this

puddle remain fairly constant during the winter months due to the

maximum size limit imposed by overflow into the culvert and to

frequent fillings from rain during this wet time of the year.

Being in a flow-through system, the flora and fauna in the ditch

are subjected to frequent washouts. In 1978, 1979, and 1980 the

site first filled in early January and contained water until the

first week in April. Washouts were frequent in January and February

but became rare in March. The site occasionally filled during other

seasons but did not hold water for extended periods. No attempt was









made to identify all the fauna in the ditch, but observations made

while collecting showed that the site contained copepods, ostracods,

amphipods, small Cladocera, Ephemeroptera nymphs, Odonata nymphs,

Diptera larvae, Coleoptera larvae and adults, Hemiptera, Rana tad-

poles, Bufo tadpoles, Hyla tadpoles, but no fish. Ostracods,

Simocephalus, and small cladocerans were observed in very large

numbers during the wet winter months, but the populations dwindled

somewhat as the pond began to dry. The bottom of the pond was

covered with submerged vegetation and some emergent vegetation.

Simocephalus exspinosus was the only Simocephalus collected at this

site. Archer was selected for an examination of the r- and K-selection

model for it is an exposed, unstained, fishless, temporary pond

that would have S. exspinosus subjected to heavy D.I. selection due

to the frequent washouts and to intense D.D. selection later as the

pond dried and the washouts no longer occurred.

The Pine site is found on the east side of S.W. 6th Street

between South Main and Waldo Road in Gainesville. It is a shaded

pond about 50m long and 30m wide that receives overflow from a

creek flowing into Payne's Prairie. It experiences no unidirectional

flow during rains, and its depth, 1.5m at most, varies with the

weather. The pond holds water for most of the year but does dry

occasionally. The water is darkly stained, and the bottom is covered

with dead leaves, allowing few submerged plants to grow, although

there are a few emergents present. Invertebrates are scarce, but

small fish are abundant and could easily invade from the nearby

branch. Both S. exspinosus and S. vetuZus were found at this site










although neither was ever very abundant. This site was chosen

for the predation studies as an example of a small, semipermanent,

shaded, darkwater pond with heavy fish predation.

Mount Vernon Pond is located north of Archer Road about 100m

northeast of the Archer site. It is a shaded, darkwater, temporary

pond with dead leaves covering the collection location. Part of

the pond has submerged and emergent vegetation, but the sample area

has neither. The pond is 20m in diameter and less than 0.5m deep.

Invertebrates are very common, and fish have been seen in parts of

the pond, but never in the collection area. The pond does dry

regularly, and fish (Gambusia affinis) are probably introduced on

an irregular basis. Simocephalus exspinosus was the only species

collected at this site.

Tennis Court Pond is a small, shaded, darkwater, temporary

pond located in the McPherson Center in southeast Gainesville.

This pond is one of the most ephemeral of those sampled. It has

a bottom covered with leaves and very little emergent vegetation.

Since it is an undrained depression, its size fluctuates with the

amount of rain. Normally it is about 5m by 10m and 0.5m deep,

although it can flood to a size of 15m by 30m. Invertebrates are

plentiful, but no fish are present. Simocephalus exspinosus was

collected at this site.

Santa Fe Pond is located on Santa Fe Community College campus

in northwest Gainesville. It is a manmade pond 50m in diameter

and 5m deep that receives runoff from the campus. It is unshaded

over most of its area, and the water is not stained. A small fringe









of submerged vegetation exists around the edges, but the bottom

lacks vegetation in deeper water. Invertebrates are common,

but fish are absent. The pond holds water for most of the year

but does dry occasionally. Simocephalus exspinosus was collected

at this site.

The smallest collection site is called the Puddle. It is

located in the Lochloosa Wildlife Management area 5m from the

northwest corner of the Still Hunt Pond site. It is a shallow

depression around an old stump and is Im by 2m and 0.25m deep.

Water from a nearby drainage ditch may seep into it during a heavy

rain, but it is quickly isolated from the ditch once the rain

stops. The bottom is covered with submerged vegetation, and some

emergents grow around the stump. The area is unshaded, and the

water in the Puddle is not stained. Invertebrates are common,

and Bufo, Hyla, and Rana tadpoles are often present. No fish are

present, but Ambystoma, a known visual predator on cladocerans

(Anderson 1968; Brophy 1980; Dodson 1970, 1974a; Hairston 1979a;

Sprules 1972), have been collected in Still Hunt Pond a few meters

away. Although Puddle and Still Hunt are close to each other,

separated by a slight rise, they are not connected during heavy

rains, and Puddle contains S. exspinosus while Still Hunt contains

S. serrulatus.

Still Hunt Pond is located just north of S.R. 346, 3km east

of the River Styx Bridge. It is a permanent lake 200m by 150m

with a depth of less than 2m. The surface is covered with

emergent and submerged vegetation. Although invertebrates are










abundant and amphibians are quite common, no fish have ever been

observed. Simocephalus serrulatus was collected at this site.

River Styx Pond is a small permanent pond located on the north

side of Alachua County Road 234 500m east of the bridge across

Camp Canal (River Styx). The pond, 20m by 50m and less than 2m

deep, is filled with submerged and emergent vegetation and is

heavily stained. Invertebrates are common, and fish are present.

The site is unshaded over most of its surface. SimocephaZus

serruZatus was collected from this site.

The River Styx Bridge site is located at the northeast corner

of the S.R. 346 bridge over the River Styx, a flowing darkwater

stream connecting Newnan's Lake and Orange Lake. This section is

usually choked with submerged, emergent, and floating vegetation.

Invertebrates are present, and fish are abundant. Simocephalus

serrulatus was collected there.

Stock Pond is located in Lochloosa Wildlife Management Area 200m

north of S.R. 346 about 1km east of the River Styx Bridge site. It

is a semipermanent pond 100m by 50m and less than lm deep. Sub-

merged and emergent vegetation cover the bottom, the site is unshaded,

and the water is not highly stained. Invertebrates are quite

abundant, amphibians are common, but fish are absent. Simocephalus

serrutatus was collected in Stock Pond.

Biven's Arm is a pair of eutrophic lakes in south Gainesville

that drain into Payne's Prairie. The two lakes are separated by

U.S. 441 although a culvert under the road connects them. The









collection site is in the downstream lake near the culvert leading

from the upper lake. The lower lake is usually covered with

emergent and floating vegetation, although spraying of herbicides

in the winter of 1980 reduced the vegetation. No Simocephalus

were collected after the spraying. Before the spraying, however,

both S. serrulatus and S. vetulus were abundant, as were other

invertebrates. Fish were always present.

Lake Alice is located on the University of Florida campus and

receives the effluent from the University sewage treatment plant. Most

of the lake is choked with vegetation, but an area 300m by 150m is

open. Samples were taken near emergent vegetation bordering the

open area. Invertebrates are quite common among the vegetation, but

fish are also present.Simocephalus vetulus was collected at this site.

Psychology Pond is a small, temporary, shaded, unstained, manmade

depression near the Psychology building on the University of Florida

campus. It is 10m by 15m and no more than 1.5m deep. The surface

is generally choked with emergent and submerged vegetation. Both

S. vetulus and S. exspinosus have been collected at this pond at

the same time, although S. vetulus may have been recently introduced

from Lake Alice by ecology classes.

Austin Carey Pond is located in the Austin Carey Memorial Forest

northeast of Gainesville. It is a small pond, 15m by 30m and 1.5m

deep, constructed for research on the white amur. Its water level

is manipulated by the researchers as is its crop of submerged veg-

etation. Invertebrates are present, and fish, in addition to the

white amur, are common.Simocephalus vetulus was found in this pond.















RESULTS


The mean rm values for the 6 cloned laboratory hearings from

the Archer site and the results of the analysis of variance of the

means (Table 5) show that the trend towards a lower rm with the

increased importance of D.D. mortality factors did not occur. No

significant difference was seen among the hearings. Other life history

parameters also showed no trends. Size at first reproduction (Table

6), age at first reproduction (Table 7), and size of newborn (Table 8)

showed no significant differences among the hearings. The differences

in death rates (Table 9) and growth rates (Table 10) did not follow

any pattern. The significant differences seen in the m(x) values

(Tables 11A and B) showed a lack of predictable trends, with the

last rearing having the consistently highest age-specific fecundity,

contrary to the prediction of the model. Age-specific size (Tables

12A and B) showed similar results. The last rearing consistently

had the largest individuals, frequently followed by individuals

from the earliest cultures.

The relationship between the age of parent and egg size (Table 13)

indicates that egg size remains constant as parents grow older.

The comparison of the size of the young from parents of different

ages (Tables 14A-E) indicates that newborn young are smaller from

early reproductions but their size stabilized quickly as the

parent matures.









The results of the food experiment did not conform to the predic-

tions of the model. The r values for the Archer clone, the Pine

clone, and the Puddle clone, hereafter known as A, B, and C, used in

the food hearings did, however, reveal a trend (Table 15). A and B

showed higher rates of increase at both high and low food levels than

did C. C did not reproduce at all at the lowest level while A and B

were able to reproduce in water passed through a 0.47 micron filter.

As food level increased, C continued to have inferior reproductive

success, never reaching the high rates of increase attained by the other

clones. Plots of r against logl0 food concentration (Table 15, Figure

1) show that the lines for A and B are not significantly different from

each other. The line for C, however, is significantly different from

B's line with regard to y intercept. Although the slope is greater

and the y intercept smaller for C's line than for the others', the

lines never cross due to C's lower r values at high food levels.

This indicates that C is more sensitive to food levels and is unable

to tolerate low levels or exploit fully high concentrations. A and

B, on the other hand, are more flexible and can maintain a relatively

high fitness over all tested food concentrations. This flexibility

can be seen by examining several life history parameters. Each

clone is examined relative to each other clone with regard to

size-specific fecundity (Table 16A-F), age-specific fecundity

(Tables 17A-F), age-specific size (Tables 18A-F), size at first

reproduction (Table 19), and age at first reproduction (Table 20).

Growth rates and death rates are found in Tables 21 and 22.









A-B: Size-specific fecundity--B was consistently greater than

A. This was probably due to the smaller size of young in B.

Age-specific fecundity--A tended to have greater fecundity

at food levels 50,000 cells/ml and above while B produced more at

lower concentrations. At levels of 1,000,000 to 50,000 cells/ml A

produced more young 26 times (9 significant) while B produced more

12 times (5 significant). A had greater fecundity only once at

the 5,000 cells/ml concentration while B was more productive 4 times

(1 significant). B always produced more young at the lowest food

level.

Age-specific size--A was consistently larger. Differences

were significant through the 500,000 cells/ml food level but

increasingly less significant as food decreased.

Size at first reproduction--A always started reproduction

at a larger size than B.

Age at first reproduction--B reproduced at a significantly

older age than A at the highest food level. The opposite was true

at the two lowest levels. Differences were not significant at

other concentrations.

A-C: Size-specific fecundity--A and C were not significantly

different at high food levels, but as food decreased A produced

significantly more young than C.

Age-specific fecundity--The trend was for A to have more

young per day than C. A's fecundity was greater 37 times (8

significant) while C's was greater 7 times (3 significant).








Age-specific size--At low food levels the two clones were not

significantly different, but as food increased A was able to increase

growth more than C, becoming significantly larger than C at the

highest food level.

Size at first reproduction--The size did not decrease for

C as food increased. A's size did, being larger than C's at the two

highest food levels and decreasing below C's at the lower concentra-

tions.

Age at first reproduction--A always produced earlier than C.

B-C: Size-specific fecundity--B was always more productive than C.

Age-specific fecundity--The trend was for B to be more

productive, being more fecund 25 times (3 significant), while C

was more fecund 11 times (2 significant).

Age-specific size--C was constantly larger than B.

Size at first reproduction--C always started reproducing at

a larger size than B.

Age at first reproduction--C was always older than B.

Summarizing, one sees that B always had the greatest size-specific

fecundity. A and C were about the same at high food levels but C

showed a much greater reduction as food levels dropped. Age-specific

fecundity was lowest at all levels for C. A outproduced B at high

food concentrations and vice versa at low levels. B had the smallest

age-specific size. A was significantly larger than C at high food

levels but became similar in size at low concentrations, sacrificing








growth for reproduction. C always had the greatest age at first

reproduction. A produced before B at high food levels and after

B at low levels. B always started reproduction at the smallest

size. A first produced young at a larger size than C at high

food and at a smaller size than C at low concentrations.

The effects of visual versus nonvisual predation were examined

by comparing S. exspinosus from a site with fish, Pine, to con-

specifics from a site without fish, Archer. Pine individuals had

a lower rm, started reproduction at an insignificantly smaller

size, reproduced at an insignificantly older age, and had larger relative

growth rates than Archer individuals (Table 23). Pine individuals

were significantly smaller at all ages (Table 24). Size-specific

fecundity was not significantly different between the two populations

(Table 25). Pine animals tended to have lower age-specific fecundity,

being less fecund 9 times (1 significant), while Archer was less

fecund 3 times (1 significant) (Table 26). Pine specimens were more

heavily pigmented than Archer specimens (Table 27). The results

from pigmentation measurements of other species and populations are

included in Table 27.

The relationship between eyespot size and body length of S.

exspinosus was examined in one habitat with no visually-oriented

predation, Archer, and in 3 habitats with such predation, Mt. Vernon,

Puddle, and Pine Ponds. Visually-oriented predation is slight and

very sporadic in Puddle and Mt. Vernon Ponds but is heavy in Pine

Pond. Identically-sized individuals collected from Archer and each

of the other sites were randomly matched, and differences in eyespot









sizes for several arbitrary body size classes of all field collected

specimens are listed in Table 28. The subsamples utilized in the

t-test clearly established that specimens of S. exspinosus from

Archer had larger eyespots than those of identical sizes from Pine

Pond (29 pairs, p < 0.05), Mt. Vernon Pond (39 pairs, p < 0.0005),

and Puddle (36 pairs, p < 0.025). In addition, no significant

differences were noted in paired observation t-tests involving all

possible combinationsof Mt. Vernon, Puddle, and Pine Ponds.

A correlation analysis (Sokal and Rohlf 1969) between the logl0

of eyespot size and the log10 of body length yielded correlation

coefficients of 0.80-Archer, 0.85-Pine Pond, 0.93-Mt. Vernon Pond,

and 0.85-Puddle. The slopes of the principal axes were 0.79-Archer,

0.76-Pine Pond, 0.70-Mt. Vernon Pond, and 0.66-Puddle. A slope of

less than1.00 indicates that the logl0 of eyespot size changes at

a lower rate than does the logl0 of body length. For values less

than 1.00, the lower the slope, the greater is the difference be-

tween the rates of change of eyespot and body sizes. Zaret and

Kerfoot (1975) suggest that the value of the slope may be inversely

related to the degree of eyespot size-selective predation. These

results appear to confirm this suggestion since the dimensions of

Archer specimens produced a higher slope than did those of the other

3 ponds' specimens.

Comparisons between field collected and laboratory-reared animals

are found in Tables 3A-I. These tables must be used carefully for

the growth rates in the field are probably not the same as in the








laboratory. The ages of field-collected animals cannot be determined

with the present data. Also, the field collections do not represent

the population in a random fashion. The tables do imply that

individuals in sites without abundant visual predators could and did

grow to a larger size, presumably due to the lack of heavy size-

selective visual predation.

Ecological differences among the three Simocephalus species can

be seen by examining life history parameters. Age-specific size

was significantly different among the species (Table 29, Figure 2),

S. exspinosus being the largest and S. vetulus the smallest. Relative

growth rates (Table 21) were highest for S. vetulus and lowest for S.

exspinosus. Size-specific fecundity was significantly different

for most sizes (Table 30, Figure 3), with S. vetulus having the

greatest values and S. exspinosus the smallest. Age-specific

fecundity values were rarely different among the species (Table 31,

Figure 4). Simocephalus serrulatus tended to be more fecund, having

the highest values 9 times (1 significant). Simocephalus exspinosus

values were greatest 3 times (1 significant) while S. vetulus were

never the most fecund. No significant differences were found among the

rm values (Table 32). Age at first reproduction was significantly

smaller for S. serrulatus than for the others (Table 33). Size at

first reproduction was significantly different among the species

(Table 34) with S. exspinosus reproducing at the largest size and

S. vetulus at the smallest. Death rates (Table 35) were somewhat

higher for S. exspinosus than for the other species. An overview









reveals that the 3 species attain similar rates of increase

through different tactics. The temporary pond species, S. exspin-

osus, grows quite large, produces the fewest but largest young

at any given body size, and begins reproduction at the largest

size. The permanent lake species, S. serruZatus, is slightly

smaller, produces more but smaller young at a given body size, and

starts reproduction at the earliest age. Simcephalus vetulus,

found in both types of habitats, is the smallest species, produces

the most but smallest young at a given body size, and starts re-

production at the smallest size.

Intraspecific interhabitat comparisons of life history parameters

are found in Tables 36A-40B. Differences seen among habitats

for S. exspinosus seem to be due to distinct differences in predation

pressures. Three habitats tend to be most highly affected by non-

visual predation, Tennis Court Pond, Santa Fe Pond, and Mt. Vernon

Pond. Two populations, Puddle and Pine, show the influence of heavier

visual predation. The Archer population has practically no predation

of either kind. Visually-oriented predation causes a shift towards

individuals with smaller age-specific size (p <.0001 after day 2,

Tables 36A and B), smaller age-specific fecundity (Table 37A and B),

and smaller size at first reproduction (p < .0001, Table 38). The

trends are reversed for populations subjected to nonvisually-oriented

predation, and the values for Archer are generally between the two

extremes. No consistent trends are evident for age at first

reproduction (Table 39), or size-specific fecundity (Table 40A and B).









The situation for S. vetulus and S. serrutatus is not as clear.

The relationship between visual and nonvisual predation is not

obvious since both types of predators are present in most habitats.

Since traits often respond in different ways to different types of

predation, only those traits, such as pigmentation, that. are

affected by only one type of predation should be compared among

sites where the relative importance of opposing selective pressures

is not obvious.

The pigmentation results for S. vetulus and S. serrulatus are

similar to those of S. exspinosus (Table 27). A significant

difference was seen between S. serrutatus from River Styx Bridge,

a site with abundant fish, and those from Stock Pond, a site with

few visual predators and abundant invertebrates. In S. vetulus,

Psychology Pond had the lightest specimens. This site has no fish

or abundant invertebrate predators. The darkest specimens came

from Pine Pond, a site with abundant fish and few invertebrates.

Specimens from Lake Alice, a lake with an abundance of both types

of predators, were intermediate with regard to pigmentation.
















DISCUSSION


The r- and K-selection model (MacArthur and Wilson 1967) is

often used to predict trends in the evolution of life history para-

meters. Its basis is found in the realization that an individual

may be placed in a habitat with abundant resources and no intra-

specific competition. The reproductive tactics that would best

insure maximum attainable fitness, the production of the maximum

number of reproductively successful offspring, for that individual

should be different from those of an individual inadescendant pop-

ulation existing at the carrying capacity of the habitat for that

species. This research tests the model by examining the reproductive

tactics of clones taken from the same continuous natural population

subjected to both extremes at different times. A continuum exists

between the two extremes, and numerous correlates are associated

with each end (Pianka 1970). Genotypes that are most fit at the r

(D.I.) end would be least fit at the K (D.D.) end of the continuum

and vice versa. As assumption central to the model is that a genet-

ically controlled tradeoff of traits should occur in the population

as D.I. selection was replaced by D.D. selection. Numerous invest-

igators have tested the validity of the model with a variety of

organisms. Stearns (1976, 1977) reviewed much of the data and

critiqued the model, reminding researchers ". .that the interpret-








ation of data is ambiguous because the theory is incomplete." (Stearns,

1977, p. 146) Good empirical data, however, must be available if

theorists are to form a realistic life history theory.

Stearns (1977) used six criteria to examine the reliability of

life history data.

A. "Did the author rear the organisms under constant conditions

to isolate the genetic component of the variability observed in the

field?" All Simocephalus for the examination of the r- and K-

model were obtained from animals reared under constant laboratory

conditions.

B. "Did the author attempt to measure the environmental factors

later invoked to explain differences in reproductive traits?" For

clones reared to observe changes in rm, no numerical values were

placed on competition, crowding, or other selective factors in

the natural habitat, but relative differences were described. Pop-

ulation estimates were not made for they would be of little use in

determining competition levels unless food concentrations were known.

Food availability would be difficult to determine accurately because

the complete diet of S. exspinosus is not known. Counts of algal

cells and bacteria would give poor estimates of food supplies because

some large or filamentous algal cells would be unusable by the clado-

ceran, and the lower size range of usable particles is quite small.

Simocephalus exspinosus have grown and reproduced in autoclaved

aquarium water passed through a 0.47 micron filter. For this study

the obvious long-term trends provided a more reliable description

of the environmental factors than a series of necessarily inaccurate

estimates. Numeric values would be essential if comparing different









populations in different habitats but would not be vital when

dealing with one habitat in which observable changes did occur.

Numeric values were placed on the factors examined in the food

experiment.

C. "Did the author attempt to measure the degree of density-

dependent or density-independent regulation?" As seen in "B,"

relative measures were used.

D. "Did the author attempt to measure year-to-year variabiltiy

in the mortality schedule?" The laboratory cloned hearings had

accurate measurements of mortality schedules, and the hearings of

several genotypes provided a measure of variability in the population.

The year-to-year variability is not important in this study that

examines variability in a population on a smaller time scale.

Variability within a clone was measured in the food experiment by

replicate rearing of members of the same clone.

E. "Were the statistics convincing? For intraspecific comparisons

were analyses of variance or covariance done?" Analysis of variance

was the statistic used most often on the data.

F. "Was an attempt made to measure reproductive effort?" Repro-

ductive effort was measured as number of young age-specifically

and size-specifically. Relative differences between hearings with

regard to the comparison of number of young versus amount of growth

would give reliable information concerning the proportion of the

total intake that went to reproduction as opposed to growth. The

number of young is a reliable index of reproductive effort over most

of the parents' lifespan for the size of the young remains quite

constant after the very earliest of reproductions.









Perhaps the most crucial of the six criteria is "A." Unless

differences in life history tactics that determine the fitness of

an organisms are genetically controlled, natural selection cannot

affect future populations. If the different test organisms are not

reared under identical conditions to insure that the only variable

is genetic, one does not know whether differences between organisms

in the field are but reflections of phenotypic plasticity. Most

workers have not examined this aspect (Stearns 1977), assuming

that variability was genetically based. Several workers have

rigorously tested, with varying results, for the genetic component

of the variability found in different populations of the same

species. Gadgil and Solbrig (1972) and Solbrig and Simpson (1977)

lent support to the model by rearing dandelions (Taraxacum) in

greenhouses and in garden plots. Genetic differences in competitive

and reproductive ability were seen that suggested the predicted

tradeoff in adaption to r- and K-selection. No tradeoff was seen,

however, in a study of Escherichia coti by Luckinbill (1978).

Instead, one genotype was seen to be superior to another during

both D.I. and D.D. control.

This study of S. exspinosus examined the genetic component of

variability among temporally separated populations by rearing the

organisms under identical conditions. The cloned hearings of

S. exspinosus from the Archer site during the winter of 1979 did

not show the tradeoff predicted by the r- and K-selection model.

The model predicts that the populations present during times of







heavy D.I. mortality would have high rm values. Heavy D.I.

mortality occurred from the time of the pond's filling in early

January until the pond no longer experienced regular washouts in

early March. As the pond began to dry, D.D. factors became in-

creasingly important, and rm values should have dropped. Contrary

to the predictions of the model, the rm values for hearings at

six dates between January 15 and March 27 showed no significant

difference. The highest rm values were actually obtained on March

27, two days before the pond dried.

Other life history parameters also indicate that the expected

tradeoffs did not occur. Among the six dates there was no significant

difference for size at first reproduction, age at first reproduction,

or size of newborn. Neither growth rates nor death rates showed

any trend. The m(x) values showed no significant differences for

most days, but when they did, March 27 clones always had the highest

values, contrary to the model's predictions. Age-specific size

measurements showed that, as expected, March 27 individuals grew

to the largest size, but the January specimens were generally the

next largest, contrary to what would be expected.

Is the shift from D.I. to D.D. selection realistic in this site?

Several things must be considered when dealing with this question.

The morphometry of the pond is such that washouts are common during

the rainy seasons. Water flows through the ditch into a culvert,

removing flora and fauna from the ditch. Runoff from the hog

farm would be high in nutrients. As a result, the population of

S. exspinosus would be reduced, and fresh water rich in nutrients









would be introduced at frequent intervals, keeping the cladoceran

population below carrying capacity and stimulating the growth of

algae and bacteria. Predation, a problem that could cloud the

results, does not seem to have a great effect on any size of S.

exspinosus in Archer Pond. Predation by fish is nonexistent, and

invertebrate predation seems to be of relatively minor importance

in controlling the population. While predatory invertebrates are

present, they are never very abundant relative to the prey species.

Vast numbers of small cladocerans, ostracods, and S. exspinosus

are present during the rainy season, suggesting that the herbivores

can reproduce themselves beyond the control of the predators. The

persistence of the Simocephalus population to a few individuals in

the last wet depressions in the ditch as it dries suggests that

predation has little effect, even when numbers are low. If one

compares the size of the field-collected individuals from Archer

to the size of the laboratory-reared animals at day 14 and to the

size of field-collected animals from the population subjected to

heavy fish predation in Pine Pond, one sees that the Archer pop-

ulation contains quite large individuals in greater numbers than

would be expected if predation were important. This information must

be used with caution but does indicate that Archer individuals

can and do escape predation long enough to grow to a large size on a

regular basis while large individuals in the Pine populations are rare.

As the frequency of washouts decreases and finally stops, the

population could reach carrying capacity, and the pond would no

longer be supplied with new water rich in nutrients. Nutrients









would be depleted or put into the standing crop of plants unusable

by Simocephalus, and competition for food would increase. As the pond

is reduced in volume, crowding would become a more important D.D.

mortality factor.

The data indicate that the Archer population did not show the

expected changes in the population parameters commonly examined.

One might expect that only one clone was present throughout the

season, and that individuals should, therefore, not reflect any

changes when reared under similar conditions at different times.

Sexual activity, however, was observed through much of the season

by the collection of males and sexual females. Evidence suggests

that Simocephalus females are capable of fertilizing their own

sexual eggs (Hebert 1980). Self-fertilization would further decrease

the probability of the population being comprised of a single clone

because recombination could occur without the presence of males.

Some S. exspinosus and S. vetulus cultured during this study,

although isolated since birth, produced both ephippia and partheno-

genetic eggs.

In order to find a possible explanation for the failure of the

population to contain different genotypes under different conditions

as predicted by the model, a food study was conducted to determine

whether S. exspinosus with high r values at high food levels had

lower r values at low food levels than specimens with low r values

at high food levels. This study showed that some clones had

higher r values over all food ranges tested than did other clones.








The other parameters commonly examined did not show a tradeoff either.

The high r clones consistently reproduced at an earlier age and had

the flexibility to reproduce at increasingly smaller sizes as food

concentrations were reduced. The high r clones had patterns of age-

specific size and size-specific fecundity that allowed greater

age-specific fecundity. The low r clone had no reproduction at the

lowest food level and had higher death rates at the lower food levels

than the high r clones. The high r clones showed greater flexibility

to changing food levels, indicating that they could adapt better to

a wide range of conditions. Since some genotypes were more success-

full at all food levels than other genotypes, the successful geno-

types would be more fit under most conditions, and, as seen in the

previous experiment, a shift towards a lower rm with increased D.D.

selection would not occur.

The size of young and eggs was seen to be consistent over the

entire life of the parent except that young were sometimes smaller

from the earliest reproductions. This rules out the possibility

of the manipulation of egg and young size as a method for regulating

the quality and quantity of offspring at various ages. Simocephalus

exspinosus produced the largest eggs and young, followed by S. ser-

rulatus and then by S. vetulus.

Numerous investigators have shown that planktonic invertebrates

respond to visual and nonvisual predation in different ways. Several

factors determine whether a certain predator can successfully catch

and eat a certain prey item: size, body structure, and pigmentation

(Confer and Blades 1975; Dodson 1970, 1972, 1974a,b; Hairston 1979a,b;









Kerfoot 1974, 1975, 1977a,b, 1978; Kerfoot and Peterson 1980; Mellors

1975; O'Brien and Vinyard 1978; O'Brien etal. 1979; Sprules 1972;

Werner and Hall 1974; Zaret 1972a, b; Zaret and Kerfoot 1975).

Size-selective predation by visual predators favors small

specimens. The visually-oriented vertebrate predators generally

prefer prey greater than 1mm (Dodson 1974b) and would impose a

limit on the maximum size to which a prey could be expected to grow.

Individuals capable of reproducing at a size below that favored

by the predators would have a great selective advantage over the

larger forms.

Size-selective predation by nonvisual predators heavily favors

large individuals. Invertebrates generally prefer prey less than

1mm (Dodson 1974b), being unable to handle larger individuals effect-

ively. A prey animal could free itself from nonvisual predation

by growing too large for the predator to eat. Invertebrate predation

would favor those individuals capable of reaching a large size

quickly.

Body structures may develop in a population in response to

predation. Cyclomorphic cladoceran populations may contain individuals

with elongated spines, expanded helmets, and other structures that

would help make them more difficult for an invertebrate predator

to handle (Dodson 1974b; Kerfoot 1975, 1977a, b, 1978; Kerfoot and

Peterson 1980; O'Brien and Vinyard 1978; O'Brien et al 1979).

These structures may serve as obstructions that do not allow the

predator to manipulate the prey successfully after it had been cap-

tured. Structures cost the individual energy otherwise usable in








growth and reproduction, thereby reducing the rate of increase for

that morph (Dodson 1974b; Kerfoot 1977b, 1975; Kerfoot and Peterson

1980; O'Brien and Vinyard 1978; Zaret 1972a, b). When visual predators

remove most of the invertebrate predators these structures are not

worth the cost, and forms without the structures would predominate

due to greater reproductive ability.

Pigmentation is not influenced by nonvisual predation but

promotes negative selection in planktonic populations subjected to

visual predation and positive selection in some populations not

subjected to visual predation. Planktonic individuals that are

heavily pigmented, with the pigmentation in the body (Dodson 1974b;

Hairston 1974a, b; Mellors 1975; O'Brien etal. 1979) or concentrated

in the eyespot (Zaret 1972a; Zaret and Kerfoot 1975), are more

conspicuous than cryptic clear individuals. Being conspicuous in-

creases predation on and selection against pigmented morphs, allowing

unpigmented forms to predominate. In the absence of visual predation,

pigmentation may help protect against photodamage (Hairston 1979a, b).

Combining these factors into an overview one sees that planktonic

populations subjected to visual predation tend to be composed of

small individuals without heavy pigmentation and lacking elongate or

expanded body structures while individuals inapopulation subjected

to nonvisual predation are generally larger with elongated or

expanded body features and heavier pigmentation.

Simocephalus, however, are not planktonic. They use a cervical

gland to attach to the substrate and filter feed from a stationary

position. Factors determining their resistance to predation are

somewhat different from those of the planktonic forms.







The results show that as the importance of fish predation, as

judged by the abundance of fish relative to the abundance of inverte-

brate predators, increased, the pigmentation in the shell, not the

eyespot, became heavier. The best contrast is between Archer and

Pine populationsof S. exspinosus. Archer Pond is devoid of fish

but has a few invertebrates capable of eating S. exspinosus, while

Pine Pond has an abundance of fish and few invertebrates. Archer

individuals showed no body pigmentation while Pine specimens were

quite dark. The difference was significant. Simocephalus vetulus

and S. serrutatus showed a similar response. A significant difference

was seen between S. serrulatus from River Styx Bridge, a site with

abundant fish, and those from Stock Pond, a site with few visual

predators and abundant invertebrates. In S. vetulus, Psychology Pond

had the lightest specimens. This site has no fish or abundant in-

vertebrates. The darkest specimens came from Pine Pond, a site with

abundant fish and few invertebrates. Specimens from Lake Alice,

a lake with an abundance of both types of predators, were intermediate

with regard to pigmentation.

Unlike planktonic cladocerans, the benthic Simocephalus would

be at a disadvantage if they were not highly colored in a habitat

containing numerous visual predators. Simocephalus most likely

escape detection by hiding against a dark background rather than

by being transparent. Their pigmentation, which is both light

and dark, produces a mottled pattern that blends into the nonuniform

substrate. A pattern of dark vertical stripes is often seen in

all three species. This pattern is used by a host of other animals

to blend with the background.









The animals used for the pigmentation study were collected from

the field, not reared in the laboratory. Because of this, environ-

mental factors may be cited as the reason for the dark coloration.

Perhaps some of the color is environmentally induced, but not all.

Specimens from the same sites were reared for many generations in

the laboratory in white surroundings and still retained a consider-

able amountof color. The quantity of the pigmentation may be affected

by the environment, but the existence of the pigmentation pattern is

under genetic control. Two habitats, Mt. Vernon and Pine, were very

similar to each other with the exception of the much greater abundance

of fish in Pine. Both sites were shaded with highly stained water.

Mt. Vernon individuals showed no pigmentation while Pine specimens did.

If the pigmentation were caused by staining of the shell from chemicals

in the water, one would expect the color to remain in the shell as it

was cast off during a molt. This was not the case. The color remained

in the animal, and the shed skin was clear. Also, if staining caused

pigmentation, one would expect to see no pigmentation in the laboratory-

reared animals.

In addition to pigmentation, other differences appeared between

populations subjected to and not subjected to heavy fish predation.

Two populations of S. expinosus lend themselves well to this comparison:

Pine's population, subjected to heavy fish predation, and Archer's

population, not subjected to visual predators. The most obvious

difference is abundance. Pine's population was never as vast as

Archer's. No attempt was made to determine the densities, but dips

of the collecting pan in Pine Pond rarely produced more than one or









two specimens while a dip in Archer Pond often produced 50 or more.

Fish predation in Pine Pond presumably kept the population quite small

at all times. Another obvious difference was the size of field-

collected individuals. Large animals were seen rarely in Pine Pond

but were common in Archer. Heavy visual predation reduced the

number of large individuals by size-selective removal. The compari-

son of the size of wild-caught animals to reared animals' sizes at

day 14 for both habitats indicates that Pine individuals reached

the larger, attainable sizes in the field less often than did

Archer specimens. While differences in population size and the size

of field-caught animals are not population parameters under genetic

control, they do help illustrate the presence of predation, the

effects of predation on the individual, and the importance of

developing defenses against visual predators.

One of the defenses seen through laboratory hearings also deals

with size. The Pine population contained specimens that did not

grow as large. Archer individuals had significantly larger age-

specific size than Pine specimens from birth through day 14. This

size difference can also be seen in the growth rate figures, with

Pine specimens reaching their asymptotic size more quickly.

Despite producing smaller young, Pine specimens were not significantly

different from Archer animals with regard to size-specific fecundity.

This is probably due to a reduction in the brood chamber volume caused

by the elongation and streamlining found in Pine specimens. The

difference in age-specific size and lack of a difference in size-

specific fecundity suggest a difference in age-specific fecundity.








Archer individuals generally had greater age-specific fecundity and,

as a consequence, had greater rm values than Pine animals.

The relationship between eyespot size and visual predation for

Simocephalus seems to follow the planktonic pattern. Eyespots of a

population of S. exspinosus subjected to no visual predation (Archer)

were significantly larger at all body ranges tested than eyespots

of three populations of the same species from sites containing some

visual predators (Mt. Vernon, Puddle, and Pine). No significant

differences were evident among the eyespots from the three latter

populations. The slope of the line produced by plotting logl0 eyespot

size against logl0 body length was greater for the Archer population

than for the other three populations, suggesting that eyespot size-

selective predation is less intense in Archer Pond than in Mt. Vernon,

Puddle, or Pine Ponds.

The three major morphological defenses against visual predation,

eyespot size reduction, body size reduction, and increased pigmentation,

seem to be selected independently of each other. Mount Vernon indivi-

duals have small eyespots, are unpigmented, but are quite large due

to intense size-selective predation by invertebrates. Such a combin-

ation of features could occur if predation by a small and infrequent

population of fish is not heavy enough to overshadow the intense

nonvisual selective pressures of numerous invertebrates or to make an

expenditure on body pigmentation energetically feasible, but is

sufficient to alter the eyespot size.

Contrasting predator avoidance tactics of planktonic invertebrates

with those of the benthic Simocephalus, one sees some similarities









but also some differences that are consistent with the different

life style.

Both types of organisms respond to visual predation by a re-

duction in the size of the individuals in the population. Visually-

oriented predators remove the larger individuals, causing selection

for those forms that can mature and reproduce at a smaller size.

In populations subjected to heavy nonvisual predation, animals grow

to a large size very quickly, reducing the threat of predation by

being too big for these predators to handle effectively.

Benthic SimocephaZus do not show the development of expanded

helmets or elongated spines when confronted with invertebrate

predation. Their growth rate is most likely high enough to allow

them to become too large too quickly for nonvisual predators. The

morphs and species of Simocephalus with the most conspicuous spines

or with the most expanded features are actually those subjected most

heavily to visual predators.

Pigmentation is quite different between the groups. Heavy

coloration of both light and dark patches provides camouflage against

a dark and uneven substrate for Simocephalus. Heavy pigmentation

in planktonic animals would make them more visible when suspended in

the water. The role of pigmentation in protection against photodamage

in Simocephalus was not investigated. Since egg-carrying females

and potentially light-sensitive newborn normally inhabit the substrate,

they are not as susceptible to photodamage as are zooplanktors. Thus

in the absence of selective pressures by visually-oriented predators,

the cost of pigmentation may surpass the benefit.









The ratio of eyespot size to body length is reduced by visual

predation in both types of animals, is reduced significantly even

by infrequent exposure to visually-oriented predation, and appears

to undergo selection independent of the selection affecting body

pigmentation.

Reproductive ability is greater for Simocephalus in forms not

subjected to visual predation while it is greater in planktonic

forms not subjected to heavy nonvisual predation. Planktonic

animals must spend energy otherwise usable for reproduction on the

production of spines or other additional body structures useful in

protection against invertebrate predation while Simocephalus must

expend energy on processes, such as pigment production, that are

protection against visual predators.

The key characteristics of the three species of Simocephalus

present in the area were examined to see if they were consistent in

local populations. Three characteristics from Ward and Whipple (1959)--

the shape of the ocellus, the presence of spinules on the vertex,

and the type of spines on the postabdominal claw--were examined from

field-collected specimens. The spination of the postabdominal claw

proved to be the best character for positive identification. The

postabdominal claw of S. exspinosus has a proximal pecten of long

spines' that are easily distinguishable from the smaller distal spines.

Simocephalus serrulatus has heavy spines along the entire length

of the claw while S. vetulus has very fine spines along the entire

length. A compound microscope was used to examine the claws after

their dissection from the animal. Although these spines were the








best character, they were difficult to see on live animals. The

shape of the ocellus is most distinctive for S. vetulus, which has

an irregular ocellus from which a line leads anteriorly. The

other species do not have this line, although some S. serrulatus

have a very long thin ocellus. The ocellus is very useful in

identifying S. vetulus but is not always conclusive due to pigmentation

or some other obstruction of the view of the ocellus. Likewise,

the tuft of spinules on the vertex of S. serrulatus is not always

conclusive. Some individuals do not show that character as well as

others. The spinules, however, were never seen on the other species.

Simocephalus exspinosus is the most rounded species, showing no sharp

angles at the vertex or hinge. Simocephalus serrulatus has an elongate

vertex with a sharp angle at the end and has a sharp point at the hinge,

often with heavy spines on it. Simocephalus vetulus has an elongate

but rounded vertex and a blunt point at the hinge. Simocephalus

vetulus, and to a lesser extent S. serrulatus, has a vertically and

posteriorly extended brood chamber that S. exspinosus does not have.

From the life history parameters and the types of habitats from

which the species of Simocephalus were collected, some general

comparisons of the ecology of the three species can be made. Consider-

able overlap exists, but certain trends are evident. The species

tend to be found in different types of habitats. Simocephalus exspin-

osus is the predominant species in temporary ponds, S. serrulatus is

found in permanent bodies of water, and S. vetulus can be found in

both types of habitats, often in the presence of one of the other

species. Simocephalus exspinosus was regularly collected from 6









sites, all temporary. One site, Pine, was filled with water during

most of the study period but has been observed dry. In this site

S. vetuZus coexists with S. exspinosus. Both of these species were

also found in Psychology Pond, but S. vetulus may have been recently

introduced from Lake Alice by ecology classes. Simocephalus exspinosus

was never collected from the same site as S. serrulatus. Simocephalus

serrulatus was regularly collected from 4 sites, 3 of them permanent.

In one site, Biven's Arms, S. serrulatus coexisted with S. vetulus.

S. vetulus was regularly collected from 5 sites, 3 permanent and 2

temporary, and coexisted with S. exspinosus in 2 and S. serrutatus

in one.

In temporary ponds ephippia production is necessary to maintain

a population between dry spells. Male and sexually female S. exspin-

osus were seen frequently in the field and occasionally produced in

the laboratory. Male and ephippia-bearing S. vetulus were observed

but no evidence of sexual reproduction in S. serrulatus was ever

observed in either the field or laboratory. This would imply that

S. serrulatus is less likely to inhabit temporary ponds than the

other species and that S. exspinosus can reestablish active pop-

ulations in ephemeral ponds most easily of the three species.

Age-specific size was significantly different for most ages

among the species, with S. exspinosus being the largest and S. vetuZus

the smallest. Growth rates show that S. vetuZus reached its asymptotic

value most quickly, followed by S. serrulatus and then by S. exspinosus.

These results suggest that S. exspinosus would do well in temporary









ponds devoid of fish predation while S. serrulatus would be at an

advantage when visual predation was heavy. The small size of S.

vetulus is not well understood. Burns (1968) demonstrated that

large cladocerans feed on larger food particles than dc small c.lado-

cerans. Perhaps S. vetulus is capable of feeding on smaller

food particles, thus reducing interspecific competition.

Size-specific fecundity was also significantly different among

the species with S. vetulus having the greatest values and S. exspinosus

the smallest. The small size of S. vetulus young allows more

young to be packed into the brood chamber. In addition, this

species develops an expanded brood chamber with the onset of re-

production so that the volume available for young is increased.

Simocephalus serrulatus also shows this expansion to a degree.

Since the species with the largest age-specific size showed the

smallest size-specific fecundity, the age-specific fecundity should

have been similar for the three species. Very little difference

was seen in the age-specific fecundity for the species. Likewise,

there was no significant difference in rm among the species.

Age at first reproduction was significantly smaller for S.

serrutatus than for the other species. This would be an advantage

in ponds containing fish.

Size at first reproduction was significantly different among the

species with S. vetulus being the smallest and S. exspinosus the

largest.

Death rates through day 14 were somewhat higher for S. exspinosus


than for the other species.









Clear interhabitat intraspecific comparisons can only be made

for S. exspinosus with the present data. The selective pressures

of predation were obviously different in several sites containing

this species. Mount Vernon, Santa Fe, and Tennis Court Ponds were

most highly affected by nonvisual predation although some visual

predators may have been present at times. The effects of heavy

visual predation by fish, salamanders, and visually-oriented

insects were seen in Puddle and especially Pine. Very little predation

of any sort was evident in Archer Pond. Differences in several life

history parameters can be attributed to varying degrees of the opposing

selective forces. Heavy nonvisual predation caused greater age-

specific size, greater age-specific fecundity, and greater size at

first reproduction in the first three sites. Heavy visual predation

caused opposite trends in Puddle and Pine Ponds. The Archer pop-

ulation, practically unaffected by either selective force, generally

had values between the two extremes.

The differences in the opposing selective forces of visual versus

nonvisual predation were not as clear in sites from which the other

two species were collected. Most sites contained both types of

predators, and accurate measurements of the intensities of each type

of selective force were not attempted. For this reason no attempt

has been made to explain differences in life history parameters on

the basis of varying selective forces on these two species. Pigment-

ation, however, appears to be affected only by visual predation, and

increases in pigmentation have been associated with increased visual

predation pressures because opposing selective forces due to nonvisual

predation do not exist for this trait.





46



Table 1. Survival rate of 3 species of Simocephalus cladocerans
to age 14 days.



S. exspinosus S. vetulus S, serrulatus

X 0.91 0.82 0.90

S2 0.029 0.044 0.012

Number of clones 40 9 5





47



Table 2. Intrinsic rate of natural increase (rm) for 3 species
of Simocephalus.



S, exspinosus S, vetulus S, serrulatus

X 0.619 0.612 0.417

S2 0.005 0.003 0.001

Number of clones 40 9 5









Table 3A. Comparison of size-specific fecundity of field-collected
and laboratory-reared S. serrulatus from the River Styx Pond.



Length of Mean number of Mean number of Number of field-
adult (mm) young (reared) eggs (field) collected adults


1.134-1.228 3.00 0 2

1.229-1.341 3.00

1.342-1.454 10.50 4.00 4

1.455-1.568 5.75 4.83 6

1.569-1.681 11.10 5.60 10

1.682-1.795 15.20 7.50 6

1.796-1.908 16.33 11.80 10

1.909-2.021 18.75 12.75 4

2.022-2.135 20.68 8.00 1

2.136-2.248 23.53 10.00 1

2.249-2.362 24.50

2.263-2.475 22.00


~-c









Table 3B. Comparison of size-specific fecundity of field-collected
and laboratory-reared S. serrutatus from Stock Pond.



Length of Mean number of Mean number of Number of field-
adult (mm) young (reared) eggs (field) collected adults


1,342-1,454 5.75--

1.455-1.568 4.40 0 3

1.569-1.681 8.14 0 1

1.682-1.795 11.11 4.75 4

1.796-1.908 13.20 4.25 4

1.909-2.021 14.25 6.80 5

2.022-2.135 17.78 11.00 4

2.136-2.248 20.83 8.00 2

2.249-2.362 -- 14.00 2

2.363-2.475 -- 22.33 3

2.476-2.588 -- 26.60 5

2.589-2.702 -- 25.67 3

2.703-2.815 -- 32.50 2

2.816-2.929 -- 38.00 2









Table 3C. Comparison of size-specific fecundity of field-collected
and laboratory-reared S. serrulatus from River Styx Bridge.



Length of Mean number of Mean number of Number of field-
adult (mm) young (reared) eggs (field) collected adults



1.229-1.341 -- 0 2

1.342-1.454 3.00 4.00 5

1.455-1.568 7.13 5.00 4

1.569-1.681 8.50 5.00 5

1.682-1.795 14.43

1.796-1.908 16.27 8.00 3

1.909-2.021 19.60

2.022-2.135 19.78

2.136-2.248 17.06 11.00 1

2.249-2.362 17.00










Table 3D. Comparison of size-specific fecundity
and laboratory-reared S. vetuZus from Pine Pond.


of field-collected


Length of Mean number of Mean number of Number of field-
adult (mm) young (reared) eggs (field) collected adults


1.134-1.228 -- 5.00 3

1.229-1.341 5.00 6.00 1

1.342-1.454 6.75 7.00 6

1.455-1.568 7.00 12.88 9

1.569-1.681 12.85 14.50 8

1.682-1.795 13.52 17.43 7

1.796-1.908 14.11 21.40 5

1.909-2.021 17.38 25.00 3









Table 3E. Comparison of size-specific fecundity
and laboratory-reared S. vetulus from Lake Alice.


of field-collected


Length of Mean number of Mean number of Number of field-
adult (mm) young (reared) eggs (field) collected adults


1.134-1.228 7.00 2.00 5

1.229-1.341 5.73 4.75 4

1.342-1.454 7.85 6.74 22

1.455-1.568 12.36 8.47 20

1.569-1.681 16.38 7.63 8

1.682-1.795 18.66 12.00 3

1.796-1.908 21.25

1.909-2.021 23.63









Table 3F. Comparison of size-specific fecundity of field-collected
and laboratory-reared S. vetulus from Psychology Pond,



Length of Mean number of Mean number of Number of field-
adult (mm) young (reared) eggs (field) collected adults



1.134-1.228 2.00 1.00 6

1.229-1.341 2.73 2.00 10

1.342-1.454 5.52 3.80 8

1.455-1.568 9.04 5.45 19

1.569-1.681 13.38 6.67 14

1.682-1.795 17.36 8.69 15

1.796-1.908 18.90 8.50 3

1.909-2.021 22.00









Table 3G. Comparison of size-specific fecundity
and laboratory-reared S. exspinosus from Archer.


of field-collected


Length of Mean number of Mean number of Number of field-
adult (mm) young (reared) eggs (field) collected adults


1.342-1.454

1.455-1.568

1.569-1.681

1.682-1.795

1.796-1.908

1.909-2.021

2.022-2.135

2.136-2.248

2.249-2.362

2.363-2.475

2.476-2.588

2.589-2.702

2.703-2.815

2.816-2.929

2.930-3.042


5.00

4.75

8.60

9.60

12.55

14.42

15.61

16.35

18.08

20.60

27.00


0

0

4.00

4.40

5.76

7.50

7.62

8.22

9.17

10.38

20.00

21.00

30.43

35.20

28.50









Table 3H. Comparison of size-specific fecundity
and laboratory-reared S. exspinosus from Pine Pond.


of field-collected


Length of Mean number of Mean number of Number of field-
adult (mm) young (reared) eggs (field) collected adults


1.229-1.341 4.00

1.342-1.454 4.17 5.09 13

1.455-1.568 5.65 5.67 3

1.569-1.681 7.45 7.00 7

1.682-1.795 12.13 7.83 12

1.796-1.908 14.69 11.50 4

1.909-2.021 15.85 11.00 3

2.022-2.135 14.60 24.00 3

2.136-2.248 12.00 7.00 1

2.249-2.362 21.00

2.363-2.475 18.00 41.00 1

2.476-2.588 5.00









Table 31. Comparison of size-specific fecundity of field-collected
and laboratory-reared S. exspinosus from Puddle



Length of Mean number of Mean number of Number of field-
adult (mm) young (reared) eggs (field) collected adults


1.455-1.568 7.00 0 1

1.569-1.681 5.71 2.00 2

1.682-1.795 7.80 1.00 2

1.796-1.908 11.90 7.00 3

1.909-2.021 15.50 7.00 2

2.022-2.135 15.80 10.60 6

2.136-2.248 17.60 15.25 10

2.249-2.362 15.57 20.50 9

2.363-2.475 18.00 20.46 14

2.476-2.588 26.00 11.67 3

2.589-2.702 -- 19.50 2

2.703-2.815 16.33 2

2.816-2.929 18.33 3

2.930-3.042 38.50 2

3.043-3.155 29.67 3

3.156-3.269 0 1






57



Table 4. Body length at age 14 days and rm values for January
and April cohorts of the same clones of Simocephalus.



Species Date r Body length (mm)
m


S. exspinosus


25 January


13 April


S. vetulus


20 January

14 April


0,706

0.702

0.579

0.580


2.61

2.59

1.89

1.91









Table 5. rm values and analysis of variance of cloned Archer
hearings. Number of generations.



Means:

Date: Jan 15 Jan 25 Feb 12 Feb 28 Mar 19 Mar 27

Mean: 0.657 0.627 0.605 0.607 0.570 0.670

n: 2 8 9 10 5 6


Analysis of variance:

f= 1.44

DF/df= 5/34
p= 0.2358

Estimate of mean generation time = 8 days

Estimate of the number of generations

of S. exspinosus in the Archer site = 10 generations









Table 6. Size at first reproduction of cloned Archer hearings.


Means:


Date:

Mean (mm):


Jan 15

1.975

2


Jan 25

1.838

8


Feb 12

1.847

7


Feb 28

1.826

10


Mar 19

1.799

5


Mar 27

2.006

5


Analysis of variance:

f= 1.61

DF/df= 5/31

p= 0.1874









Table 7. Age of first reproduction of cloned Archer hearings,



Means:

Date: Jan 15 Jan 25 Feb 12 Feb 28 Mar 19 Mar 27

Mean (days): 4.00 3.88 4.33 4.30 3.80 4.17

n: 2 8 9 10 5 6

Analysis of variance:

f= 0.8200

DF/df= 34/4

p= 0.5425









Table 8. Size of newborn of cloned Archer hearings.


Means:

Date:

Mean (mm):

n:


Jan 15 Jan 25 Feb 12

0.803 0.770 0.756

2 8 7


Feb 28 Mar 19

0.743 0.756

10 5


Analysis of

f=

DF/df=

p=


Mar 27

0.745

5


variance:

1.01

5/31

0.4284


I __


__ ___









Table 9. Death rates (number of dead/number of days lived) of
cloned Archer hearings through day 14.



Date Death Rate



Jan 15 0.0155, 0

Jan 25 0.0233, 0.0155, 0, 0, 0, 0, 0, 0

Feb 12 0.0229, 0.0240, 0.0072, 0.0182, 0, 0, 0, 0, 0, 0

Feb 28 0.0164, 0.0092, 0, 0, 0, 0, 0, 0, 0, 0

Mar 19 0.0930, 0.0816, 0.0825, 0.0164, 0.0632, 0.0612

Mar 27 0, 0, 0, 0, 0










Table 10. Growth rates of cloned Archer hearings.


Growth Rate


0.718

0.462

0.560

0.590

0.584

0.558


Date


Jan

Jan

Feb

Feb

Mar

Mar


_ __ ___
__


_ _~___ _


I__ _









Table 11A. m(x) of cloned Archer hearings; means.


Days 15Jan 25Jan 12Feb 28Feb 19Mar 27Mar



3 --- 1.85 --- 5.00 1.11 --

4 7.35 5.58 4.60 5.04 4.93 7.90

5 6.25 3.65 6.20 7.40 6.69 4.92

6 10.60 8.95 8.88 8.13 4.27 17.44

7 10.28 5.52 9.45 6.78 3.00 7.13

8 16.00 12.67 9.77 2.68 6.01 26.20

9 18.72 7.23 6.40 7.96 8.52 14.76

10 2.55 12.82 6.24 4.91 14.25 20.68

11 12.05 7.38 7.65 9.29 3.90 7.05

12 4.45 13.90 8.13 5.46 5.79 21.38

13 12.92 7.63 11.23 10.14 11.75 8.56

14 4.92 13.57 7.41 5.65 10.63 18.10









Table 11B. m(x) of cloned Archer hearings; analysis of variance



Day DF/df f p Duncan's Multiple Range Test



3 2/2 8.35 .1070

4 24/5 0.55 .7338

5 5/30 1.02 .4219

6 5/31 4.62 .0029 Mar27 Janl5 Jan25 Febl2 Feb28 Marl9


7 5/26 1.24 .3190

8 5/28 25.44 .0001 Mar27 Janl5 Jan25 Febl2 Marl9 Feb28


9 5/30 2.09 .0949

10 5/28 9.71 .0001 Mar27 Marl9 Jan25 Febl2 Feb28 Janl5

11 5/25 1.40 .2584

12 5/29 14.49 .0001 Mar27 Jan25 Febl2 Marl9 Feb28 Janl5

13 28/5 0.57 .7214

14 5/29 6.78 .0003 Mar27 Jan25 Marl9 Febl2 Feb28 Janl5









Table 12A. Age-specific size of cloned Archer hearings; means
in mm.



Day Jan 15 Jan 25 Feb 12 Feb 28 Mar 19 Mar 27


0.7182

1.1529



1.8900



2.0601



2.2302



2.3436



2.4381



2.4570

2.6082


0.7749

1.0331

1.4364

1.7388

1.7993

2.0915

2.0261

2.2680

2.1848

2.3814

2.3587

2.4948

2.4268

2.5704

2.4948


0.7560

0.9639

1.3230

1.7199

1.7766

1.9940

2.0412

2.1924

2.2049

2.2208

2.3814

2.2964

2.4317

2.3720

2.4948


0.7447

0.9136

1.3608

1.5751

1.9562

1.7955

2.0885

1.9531

2.1357

2.0726

2.2302

2.3058

2.3720

2.3814

2.4381


0.7466



1.3041



1.8617



1.9467



2.0412



2.1735



2.2491



2.3058


0.7258



1.4440



1.9656



2.2151



2.3965



2.5024



2.6233



2.6989









Table 12B
of variance.


Age-specific size of cloned Archer hearings; analysis


Day DF/df f p Duncan's Multiple Range Test


0 5/30

1 3/11

2 16/4

3 3/11

4 4/16

5 3/11

6 4/16


7 3/11

8 4/16


9 3/11


10 4/16


11 3/11

12 4/16


13 3/11


14 5/15


1.17

3.90

0.91

2.53

2.37

6.59

4.56


.3462

.0403

.4792

.1108

.0965

.0082

.0119


17.27 .0002

14.15 .0001


18.14 .0001


8.96


.0005


11.09 .0012

11.25 .0002


8.45


.0034


16.37 .0001


25Jan 15Jan 12Feb 28Feb

27Mar 28Feb 12Feb 25Jan 19Mar


25Jan 15Jan 12Feb 28Feb

27Mar 12Feb 25Jan 28Feb 19Mar


25Jan 15Jan 12Feb 28Feb


27Mar 12Feb 25Jan 28Feb 19Mar


25Jan 15Jan 28Feb 12Feb

27Mar 12Feb 25Jan 28Feb 19Mar


25Jan 15Jan 28Feb 12Feb


27Mar 15Jan 12Feb 25Jan 28Feb 19Mar





68



Table 13. Size of eggs as a function of age of parents,


Day n Mean (mm) DF/df f p Duncan


Austin Carey S. vetulus
3 22 .1986 3/140

8 35 .1963

14 37 .1954

25 50 .2076
Biven's Arm S. serrulatus
4 7 .2116 3/42

5 7 .2076

10 11 .1965

25 21 .2081
Biven's Arm S. vetulus
4 12 .1948 3/50

10 9 .2024

15 10 .2052

25 23 .1972
Mt. Vernon S. exspinosus
3 11 .2375 4/47

8 11 .2484

13 9 .2494

19 10 .2153

25 11 .2175
River Styx Pond S. serruZatus
6 41 .1990 100/2

11 28 .2001

17 34 .2013


6.70









12.61









1.93









45.84











0.38


.0004 25 3 8 14









.0001 4 25 5 10









.1375









,0001 13 9 3 25 19











.6842









Table 14A. Size of young born to parents of
S. exspinosus collected from Mt. Vernon Pond.


various ages in


Day n Mean (mm)


4-5-6 28 0.6872

7-8-9 10 0.7106

10-11-12 10 0.6804

13-14-15 10 0.7182

16-17-18 20 0.7182

19-20-21 21 0.7235

33 5 0.7182



Analysis of variance df f p
6/97 10.61 .0001

Duncan: 19-20-21 33 13-14-15 16-17-18 7-8-9 4-5-6 10-11-12










Table 14B. Size of young born to parents of various ages in
S. vetulus collected from Austin Carey Pond,



Day n Mean (mm)


3-4 37 0.5129

5-6 16 0.5436

7-8 51 0.5761

9-10 56 0.5655

11-12 40 0.5538

13-14 16 0.5625

15-16 37 0.5681

17-18 38 0.5689

19-20 45 0.5685

21-22 50 0.5708

23-24 31 0.5708



Analysis of variance: df f p
10/406 29.61 .0001

Duncan: 7-8 21-22 23-24 17-18 19-20 15-16 9-10 13-14 11-12 5-6 3-4









Table 14C. Size of young born to parents of
S. vetulus collected from Biven's Arm.


various ages in


Day n Mean (mm)


3-4-5 34 0.5337

6-7-8 21 0.5761

9-10-11 28 0.5670

12-13-14 10 0.5760

15-16-17-18 24 0.5760

20-22-23 25 0.5760



Analysis of variance: df f p
5/136 9.68 .0001

Duncan: 6-7-8 9-10-11 12-13-14 20-22-23 15-16-17 3-4-5










Table 14D. Size of young born to parents of various ages in
S. serrutatus collected from Biven's Arm.



Day n Mean (mm)


4-5 25 0.5776

6-7 39 0.5893

8-9 25 0.5957

10-11 15 0.5923

12-13 15 0.6048

14-15 22 0.6101

16-17 25 0.5972

18-19 25 0.5972

20-21 25 0.5972



Analysis of variance: df f p
8/207 2.43 .0156

Duncan: 14-15 12-13 16-17 18-19 20-21 8-9 10-11 6-7 4-5









Table 14E. Size of young born to parents of various ages in
S. serrulatus collected from River Styx Pond.



Day n Mean (mm)


3-4 63 0.6010

5-6 49 0,6294

7-8 50 0.6313

9-10 30 0.6301

11-12 45 0,6301

13-14 55 0.6188

15-16 39 0.6377



Analysis of variance: df f p
6/324 15.21 .0001


Duncan: 15-16 13-14 7-8 9-10 11-12 5-6 3-4








Table 15. Relationship between food level and r of 3 different
lines of S. exspinosus.
A. r values of the S. exspinosus food hearings.
B. Characteristics of plots of r-logl0 food level.
C. Analysis of covariance of lines in "B".



A. Food (cells/ml) A B C



1,000,000 .568 .550 .473

500,000 .547 .527 .450

250,000 .466 .448 .407

50,000 .368 .401 .204

5,000 .204 .286 .002

0 .019 .086



B. Clone Slope y intercept x intercept Correlation


A .092 -0.027 0.299 .96

B .075 0.062 -0.827 .98

C .209 -0.753 3.61 .99


C. A/B A/C B/C

slope;
p= .3346 .0090 .0003

y intercept;
p= .5726 .1810 0.135



























.4


4,
.4
.4
.4
.4
.4
.4


.1

i

02U


i-I iI
CO CC.
*


- CD


0



.,-
- ~NC









Table 16A. Size-specific fecundity of 3 lines of S. exspinosus at
a food level of 1,000,000 cells/ml.



mm A B C p Duncan


1.229-1.341 ---- 5.00

1.342-1.454 ---- 6.67 ---

1.455-1.568 ---- 8.25 3.33 .0006

1.569-1.681 6.00 10.17 5.50 .0023 B A C

1.682-1.795 8.00 10.67 9.60 .4830

1.796-1.908 9.67 15.20 13.67 .3767

1.909-2.021 15.40 18.33 13.33 .1100

2.022-2.135 10.50 23.80 14.29 .0035 B C A

2.136-2.248 17.00 31.00 16.83 .0002 B A C

2.249-2.362 21.00 ---- 19.40 .1652

2.363-2.475 19.36 --- ---

2.476-2.588 19.00 --- ---









Table 16B. Size-specific fecundity of 3 lines of S. exspinosus at
a food level of 500,000 cells/ml.



mm A B C p Duncan


1.229-1.341 ---- 8.00

1.342-1.454 ---- 6.00 ---

1.455-1.568 4.00 9.17 4.00 .0139 B A C

1.569-1.681 5.25 9.33 5.00 .0001 B A C

1.682-1.795 9.33 13.57 10.00 .1109

1.796-1.908 14.50 17.11 14.25 .0695

1.909-2.021 17.50 19.50 14.20 .0913

2.022-2.135 20.83 ---- 15.33 .0004

2.136-2.248 20.57 ---- 17.00 .0024

2.249-2.362 19.00 ---- 17.00 .2026

2.363-2.475 21.50 ----








Table 16C. Size-specific fecundity
a food level of 250,000 cells/ml.


of 3 lines of S. exspinosus at


mm A B C p Duncan


1.342-1.454

1.455-1.568

1.569-1.681

1.682-1.795

1.796-1.908

1.909-2.021

2.022-2.135

2.136-2.248


4.33

6.44

8.83

10.78

14.60

15.20


4.00

6.00

10.50

8.67

10.29

10.44

10.00


4.00

4.00

6.83

6.25

11.00

10.60

7.67


.0661

.0027

.0015

.0055

.0094

.9421

.5938


B A C

B A C

B A C

B C A
BGA









Table 16D. Size-specific fecundity
a food level of 50,000 cells/ml.


of 3 lines of S. exspinosus at


mm A B C p Duncan



1.229-1.341 ---- 3.25 ---

1.342-1.454 2.00 4.71 1.00 .0012 B A C

1.455-1.568 3.33 6.20 2.00 .0001 B A C

1.569-1.681 5.67 6.30 2.75 .0124 B A C

1.682-1.795 6.80 7.00 3.25 .0408 B A C

1.796-1.908 9.00 3.50 .0041

1.909-2.021 9.83 --- 3.00 .0077

2.022-2.135 10.67









Table 16E. Size-specific fecundity of 3 lines of S. exspinosus at
a food level of 5,000 cells/mi.



mm A B C p Duncan



1.229-1.341 --- 2.50 ---

1.342-1.454 1.75 3.71 ---- .0013

1.455-1.568 2.33 --- 4.75 .0009

1.569-1.681 3.00 4.67 5.00 .0041 C B A

1.682-1.795 3.00 --

1.796-1.908 4.50 --- 5.00 .6667




81



Table 16F. Size-specific fecundity of 3 lines of S, exspinosus at
a food level of 0 cells/ml.



mm A B C p



1.229-1.341 --- 1.40 ---

1.342-1.454 1.25 3.00 ---- .0106

1.455-1.568 1.33 2.50 --- .1328

1.569-1.681 1.00 ---









Table 17A. Age-specific fecundity of 3 lines of S. exspinosus at a
food level of 1,000,000 cells/ml.


Day A B C p Duncan


4 6.80 --- ---

5 11.17 8.17 3.25 .0415 A B C


6 15.50 7.50 8.33 .0174 A C B

7 16.00 9.40 11.40 .0054 A C B

8 15.00 15.33 13.50 .8822

9 20.00 16.33 12.75 .1165

10 18.33 20.17 16.67 .8009

11 19.60 19.33 15.80 .0439 A B C


12 19.33 22.60 21.00 .7279

13 19.40 15.67 15.60 .1501

14 19.00 16.60 18.00 .9105









Table 17B. Age-specific fecundity of 3 lines of S. exspinosus at a
food level of 500,000 cells/ml.


Day A B C p Duncan


4 5.25 --- ---

5 4.50 8.29 3.50 .0018 B A C

6 10.00 8.00 9.00 .7643

7 15.33 11.80 9.17 .1869

8 18.17 9.33 17.00 .0082 A C B

9 19.50 13.67 13.83 .0957

10 21.20 16.00 17.50 .0279 A C B


11 20.67 ---- 13.67 .0043

12 20.60 12.67 18.00 .0598

13 21.00 20.00 16.00 .1427

14 16.67 17.67 16.50 .9129









Table 17C. Age-specific fecundity of 3 lines of S. exspinosus at a
food level of 250,000 cells/ml.


Day A B C p Duncan


5.50

4.33

8.50

9.17

10.50

12.67

8.25

10.00

10.00

12.67

8.00


6.25

5.33

9.00

7.50

9.67

11.67

14.00

7.67

13.67

10.00


8.75



4.50

12.50

6.00

12.67

5.00

7.00

7.67

5.00


.0001

.0432

.0442

.0753

.0768

.3685

.0040

.4490

.0739

.5224


C B A



A B C








B A C
BAG









Table 17D. Age-specific fecundity of 3 lines of S. exspinosus at a
food level of 50,000 cells/ml.



Day A B C p Duncan


5 4.50 4.00 ---- .5908

6 2.75 4.50 3.00 .1239

7 6.50 7.00 3.00 .2866

8 5.33 6.50 2.67 .2470

9 9.00 6.00 2.50 .1484

10 7.17 6.00 4.00 .3241

11 10.00 6.20 ---- .0188

12 8.00 5.50 2.67 .0983

13 12.00 6.80 3.00 .0117 A B C

14 7.00 4.50 2.67 .0501









Table 17E. Age-specific fecundity of 3 lines of S. exspinosus at a
food level of 5,000 cells/ml.



Day A B C p Duncan


4 --- 4.00

6 ---- 2.25 ---

7 2.50 4.50 --- .3333

8 2.00 4.00 5.00 .0029 C B A

9 3.00 4.67 ---- .0068

10 2.00 4.00 ---- .0748

11 2.75 4.00 ---- .4397

12 2.00 5.00 5.00 .0000 B C A

13 4.00 4.00 ---- 1.00

14 3.00 5.00 ---- .0000





87



Table 17F. Age-specific fecundity of 3 lines of S. exspinosus at a
food level of 0 cells/ml.



Day A B C


8 ---- 1.67 ---

10 ---- 2.33 ---

11 1.25 --- ---

12 --- 2.33 -

13 1.25 --- --

14 ---- 2.50






88


Table 18A. Age-specific size of 3 lines of S. exspinosus at a
food level of 1,000,000 cells/ml.


Means (mm)
Day A B C p Duncan


0.7798

1.0020

1.3041

1.6020

1.6776

1.8806

2.0461

2.1406

2.2019

2.2729

2.3202

2.3531

2.4098

2.4336

2.4619


0.7371

0.8316

1.0350

1.2712

1.4791

1.5026

1.6303

1.7059

1.7577

1.8617

1.8995

1.9656

1.9800

1.9940

1.9989


0.7371

0.8222

1.0301

1.2145

1.4270

1.5075

1.7815

1.8099

1.9373

2.0223

2.1168

2.1735

2.2302

2.2351

2.2869


.0015

.0001

.0001

.0001

.0009

.0001

.0001

.0001

.0001

.0001

.0001

.0001

.0001

.0001

.0001


B C

B C

B C

B C

B C

C B

C B

C B

C B

C B

C B

C B

C B

C B

C B









Table 18B. Age-specific size of 3 lines of S. exspinosus at a
food level of 500,000 cells/ml.


Means (mm)
Day A B C p Duncan


0.7844

0.9828

1.2569

1.4270

1.5736

1.7343

1.8004

1.9138

1.9989

2.0745

2.1312

2.1973

2.2208

2.2732

2.3274


0.7420

0.8316

1.0017

1.2002

1.3986

1.4697

1.5264

1.6349

1.7343

1.7672

1.8193

1.8144

1.8575

1.8632

1.9429


0.7371

0.8554

0.9972

1.1718

1.4081

1.5264

1.7248

1.7861

1.9327

1.9656

2.0737

2.0934

2.1641

2.1784

2.2162


.0001

.0013

.0002

.0021

.0168

.0001

.0002

.0006

.0011

.0002

.0001

.0001

.0001

.0001

.0001


A B C

A C B

A B C

A B C

A C B

A C B

A C B

A C B

A C B

A C B

A C B

A C B

A C B

A C B

A C B
ACB