A phylogenetic approach to the evolution of mammalian genital form, with emphasis on the megachiropteran bats

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A phylogenetic approach to the evolution of mammalian genital form, with emphasis on the megachiropteran bats
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A PHYLOGENETIC APPROACH TO THE EVOLUTION OF MAMMALIAN
GENITAL FORM, WITH EMPHASIS ON THE MEGACHIROPTERAN BATS












By

RONALD EDWARDS


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

UNIVERSITY OF FLORIDA


1997































Copyright 1997

by

Ronald Edwards















ACKNOWLEDGMENTS


Thanks are due to my friends, Cecilia Friberg, Gabrielle Brady, Kas Short, Mari

Schindele, Andrew Zimmerman, Matt Jones, Lawrence Collins, and Dustin Penn for

unfailing support and encouragement; to my family, especially Margot Edwards, David

Edwards, and Forrest Edwards; to the members of my graduate committee, Larry

McEdward, Michael Miyamoto, Donald Dewsbury, Charles Woods, and my long-

suffering advisor, Richard Kiltie; to fellow scientists who have provided specimens,

references, and arguments over the years, including Bruce Patterson, Philip Hershkovitz,

Jack Fooden, Lawrence Heaney, William Stanley, Jeremy Dahl, Juan Carlos Morales,

David Huckaby, Diane Kelly, John Bertram, Craig Hood, James Ryan, William Eberhard,

Karl Koopman, J.D. Pettigrew, and Alan Dixson; to my co-author Julian C. Kerbis

Peterhans for his aid in the macroglossine project; to my undergraduate advisor Howard

Moltz, and to Mark Blumberg and Julie Menella; to Robert Liu for his assistance with

PAUP; to illustrators Kathy Toffer and Daryl Harrison for their depictions of anatomy used

in Chapter Six; to Joanna Lambert for consults on primate phylogeny; and to faculty who

have provided friendship and ideas, including Lou Guillette, Carmine Lanciani, Brian

McNab, John Eisenberg, and James Lloyd.















TABLE OF CONTENTS

page


ACKN OW LEDGM ENTS ................................................................................................. iii

ABSTRA CT ...................................................................................................................... vii

CHAPTER ONE: INTRODUCTION ................................................................................ 1

G o als .............................................................................................................................. 3
D e sig n ............................................................................................................................ 5

CHAPTER TWO: PERSPECTIVES ON GENITAL DIFFERENTIATION ............. 10

The M issing Overview ............................................................................................ 10
Entom ological Hypotheses ..................................................................................... 12
M am m alogical Hypotheses ..................................................................................... 15
A Broader View ....................................................................................................... 17
Rodent copulatory behavior .............................................................................. 18
Toward plurality .............................................................................................. 21

CHAPTER THREE: HOMOLOGY, DEVELOPMENT, AND BACULAR
DIVERSITY ................................................................................................................ 24
Hom ology and Synapom orphy .............................................................................. 25
Developm ental Levels ........................................................................................... 28
Bacular Developm ental M echanics ......................................................................... 30
Bacular composition ......................................................................................... 31
Induction and m aturation ................................................................................... 34
Evolutionary Implications ....................................................................................... 38

CHAPTER FOUR: GENITALS AND MAMMALIAN SYSTEMATICS ............... 43
The Colugo Penis and the Archontan Question ..................................................... 44
Background ....................................................................................................... 44
Colugo penis anatomy ....................................................................................... 46
Phylogenetic comparisons ................................................................................ 47
D iscu ssio n ............................................................................................................. 5 1



iv









System atics and Phylogenetic Truth ....................................................................... 55
System atic protocols .......................................................................................... 55
Positivism .............................................................................................................. 57

CHAPTER FIVE: THE PHYLOGENETIC APPROACH TO GENITAL
CHARACTER EVOLUTION: QUALITATIVE FEATURES ............................ 60
The Phylogenetic Com parative M ethod ................................................................ 60
H istory and adaptation ..................................................................................... 64
Phylogenetic A nalyses ........................................................................................... 66
The m am m alian cloaca ....................................................................................... 67
B acular loss in carnivorans and prim ates .......................................................... 72
B acular loss in the M icrochiroptera ................................................................ 75
Further Studies ....................................................................................................... 77

CHAPTER SIX: EVOLUTION OF MALE AND FEMALE GENITAL
MORPHOLOGY IN THE NOMINAL SUBFAMILY
MACROGLOSSINAE (CHIROPTERA, PTEROPODIDAE) ............................ 79
B ackground .................................................................................................................. 80
M ethods ...................................................................................................................... 83
Specim ens .............................................................................................................. 83
A nalysis ................................................................................................................. 84
R esults ......................................................................................................................... 85
M orphology .................................................................................................... 85
N um erical results .............................................................................................. 94
D iscussion ................................................................................................................... 99

CHAPTER SEVEN: THE PHYLOGENETIC APPROACH TO GENITAL
CHARACTER EVOLUTION: QUANTITATIVE FEATURES ............................ 102

G oals .......................................................................................................................... 102
Phylogeny of B acular Scaling in Prim ates ................................................................. 105
B acular length and copulatory behavior .............................................................. 105
M ethods .............................................................................................................. 107
R esults ................................................................................................................. 110
D iscussion ........................................................................................................... 114
B acular Shape and Size in the M egachiroptera .......................................................... 116
Three phylogenies ............................................................................................... 116
The m odel ............................................................................................................ 122
R esults ................................................................................................................. 125
D iscussion .......................................................................................................... 134

CH A PTER EIGH T: C ON CLU SION S ........................................................................... 138

G oals .......................................................................................................................... 138










Research Summ ary .................................................................................................... 140
Science in Action ....................................................................................................... 142

APPEND IX A ................................................................................................................. 144

APPEND IX B ................................................................................................................. 146

LIST OF REFERENCES ................................................................................................. 148

BIOGRAPHICAL SKETCH .......................................................................................... 169














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

A PHYLOGENETIC APPROACH TO THE EVOLUTION OF MAMMALIAN
GENITAL FORM, WITH EMPHASIS ON THE MEGACHIROPTERAN BATS

By

Ronald Edwards

December 1997

Chairman: Richard Kiltie
Major Department: Zoology

Description of genital form is a component of many subdisciplines of biology,

including taxonomy, systematics, development, morphology, and behavior. The
mammalian penis and the baculum of several orders are commonly described and

previously have been analyzed in relation to body size. Theory to explain the observed

diversity remains elusive, throwing any conclusions from within subdisciplines into

question. Hypotheses such as lock-and-key species isolation, female choice,

biomechanical selection between male and female, and even lack of selection are here

deconstructed into three assumptions: whether selection occurs, whether it operates on

anatomy alone or on other aspects of copulation, and whether it operates between taxa or

within them. These issues permit verifying selective or other evolutionary hypotheses

regarding differences in genital form.

Developmental studies of rodents suggest that bacular shape variation is the

product of epigenetic, rather than direct genetic change. The tradition of using genitals in









systematic revision is contra-indicated, demonstrated here with the description of the

male genitalia of the colugo (Cynocephalus volans, Order Dermoptera), and its role in the

controversy surrounding the relationships of the superorder Archonta. Adding rigorous

evolutionary perspective to comparisons between taxa is required, demonstrated here by

cloacal anatomy, patterns of bacular loss, and bacular-body size relationships in primates.

Megabats (Megachiroptera, Chiroptera) are diverse in body size and bacular diversity.

Shape and size of the bacula of 18 genera are described by qualitative measures, linear

measures, and curvature measures by means of elliptical Fourier analysis and principal-

components analysis. Two approaches, phylogenetic mapping and comparison by

independent contrasts, are synthesized and three tests conducted. (1) Megabat penis and

baculum shape are not subject to direct selection by the features of uterine and cervical

shape; lock-and-key selection in the mechanical sense is apparently not operating in these

animals. (2) Change in megabat bacular size does not scale with change in body size

across evolutionary transitions; the megabat pattern of bacular change is more punctuated

than that observed in primates. (3) The relationship between bacular width and proximal

bifurcation is conserved across megabat taxonomic change: it may be altered drastically

within its limits but itself cannot be altered.















CHAPTER 1


INTRODUCTION

... the fig leaf is a romance with which human optimism veils the only two eternal
and changeless and rather unlovely realities of which any science can be certain.
(Cabell 1927)


The biology of genital form has been studied from diverse perspectives, including

investigations of aging and developmental stages, systematics and speciation theory,

hormonal effects and cycles, body size (scaling), and mating systems. Despite such a

broad range of approaches, there is no unified system of knowledge regarding genitalic

evolution. None of the above topics has provided a system of thought regarding genital

diversity that allows results from one topic of study to be corroborated with those from

another, nor has there arisen any overarching theory to link them together as a set of

related research efforts. The result of this diffuse and murky context is to throw all

results generated to date into a kind of intellectual vacuum where everything is interesting

but nothing actually qualifies as knowledge.

This is not to say that researchers have not been asking important evolutionary

questions. Eberhard (1985, 1990) asked why male intromittent organs are so much more

diverse than female genitals; Patterson (1983) asked why rodent bacula vary highly

interspecifically relative to intraspecifically; and Dixson (1987a, 198T) asked whether









sexual selection on primate behavior is reinforced by morphology. These and many other

studies were not trivial, but their conclusions have not added up to a unified body of

knowledge. Presently, the question of why animal genitalia are anatomically distinctive

remains unanswered.

By contrast, the evolutionary circumstances producing diversity in mammalian

reproductive cycling, for instance, are well established. The selective effects are food

availability, food energy content, longevity, and predictable environmental cues, as well as

body size and mating system (Bronson 1985). The rate and seasonality of any mammal's

estrous cycle may be hypothesized given some knowledge of these variables; if tested,

and if they do not conform to the hypothesis, the animal presents a conceptual anomaly

that needs to be explained. Similar paradigms (sensu stricto, after Kuhn 1970) exist for

tooth and limb morphological diversity, metabolic rate patterns, and community

interactions based on seed dispersal. But nothing of the sort exists for genitalic diversity.

In hopping mice (genus Pseudomys), for example, sperm morphology, penis shape,

vaginal shape, copulatory behavior, and mating system are all considerably different from

those of other rodents (Breed 1989), but it remains unknown how this entire complex of

features, in this taxon, has come to change so drastically.

That genitals represent a truly mysterious topic in the study of evolutionary

processes is demonstrated by the controversies that arise. In this study alone, three of

the most provocative and at times acrimonious modern debates in biology are concerned:

(1) the roles of adaptation and homology in determining anatomical form, (2) the criteria

for including characters in phylogenetic matrices, and (3) the appropriate use of









phylogeny in the comparative method. None of these issues is currently resolved enough

to provide a cross-disciplinary standard set of techniques or assumptions, and all are

crucial to understanding population-level shifts in organismal form. To answer the

question posed above, the study must acknowledge the controversies and, for each, the

implications of one or another outlook for its results.



Goals

My fundamental question is, what leads genital form to undergo changes in shape

among taxa? This dissertation represents the first analysis of genital variation to address

this question directly. Its explicit purpose is to provide an evolutionary basis for

research on genital form, so that further studies of genitals from any research perspective

may be compared, and shown to be mutually supportive or falsifying. This basis is the

phylogenetic approach to the comparative method: parcelling variation by its position in

the cladistic hierarchy to identify and analyze instances of evolutionary change.

Answering this question requires an among-species, not within-species approach.

Arnqvist (1997) asserts that the actual, direct selective effect operating on the genital

form of a given population can only be ascertained by studying that population, but such

a study will not reveal the answer to the inter-taxa question: why does genital form

change? What effect, if any, consistently coincides with or precedes these events?

Other related questions are also not completely answerable with within-species

studies. Is genital form a target of direct selection, which is balanced against selection on

other features to yield overall fitness? Or is it a corollary, or even side-effect, of









evolutionary processes such as female selection for markers of male vigor (sensu Mikkola

1994, Harcourt 1997)? To answer these questions, the phenomena must be studied in

terms of repetitive, species-level instances, which a single species cannot provide.

Perhaps the main reason this question has proven so intractable is that shared

genital features are distributed non-taxonomically: they are phyletic in the sense that they

may be recognized as characteristic of taxa or groups of taxa, yet they are rarely

taxonomically diagnostic, because shifts in genital form do not coincide with shifts in

other features that define higher or lower taxa. Although certain genital features may be

species-specific, they are more likely to characterize a species group, or perhaps a group

of genera within a family, and other genital features may characterize several, but not all

families within an order. Few, if any, polytypic orders are characterized by a single penis

type. Furthermore, different genital features may be extremely homoplasic within an

order or family. The general pattern is a mosaic of nested, sometimes repeated events

that do not coincide with other physical changes taken to represent higher taxa.

How to analyze such a pattern? Neither of the two historical options, systematics

and the traditional comparative method, is sufficient. The first simply employs the

features in question, usually qualitative, in a systematic revision (e.g. Lidicker and Brylski

1986, Hood 1989), with a post hoc evolutionary interpretation of the resultant

distribution of taxa. This approach is sufficient when the distribution of genital changes

coincides with named groups, which is sometimes the case. The second compares

continuous variables using species (or higher taxa) as independent data points, ignoring

phylogenetic associations. One might regress bacular length against body size (e.g.









Scheffer and Kenyon 1963, Patterson and Thaeler 1982), or analyze the variance of

bacular length relative to genus membership or social system (e.g. Long and Frank 1968,

Dixson 1987a). This approach would only be sufficient if the taxa involved were not

nested in a phylogenetic hierarchy, which is never the case. For answering the general

question across many mammal species, neither option is acceptable.

The technique here employed is to summarize intertaxon variation by phyletic

position, and then to analyze those summaries. Comparisons are made (1) among

separate genital features, for instance penis and bacular features, or different aspects of

bacular size or shape; (2) between male and female genital features, such as glans penis

shape and cervical morphology; and (3) genital features and other aspects of the organism,

especially body size but also, where possible, social/mating system. For qualitative

features, the simple positions of features mapped onto a phylogenetic tree convey

evolutionary information regarding cospeciation, coadaptation, and homoplasy (Brooks

and McClennan 1991). For quantitative (and some qualitative) features, comparative

analysis by independent contrasts (Felsenstein 1985, Harvey and Pagel 1991) permits

variance-based analyses such as regressions and factor analysis.



Design

The baculum is a bone in the penis of many bats, primates, carnivorans, and all

rodents. The bone was referred to only as the ospenis until Thomas (1915). It may be

the source of the highest ratio of published observations to analyses in vertebrate

anatomy; there are hundreds of publications describing bacula, only a few dozen that









compare measurements, and less than ten addressing their evolutionary circumstances.

Yet as Patterson (1983), Eberhard (1985, 1990), and Williams-Ashman (1990) all assert,

there is no reason to expect that the bone is not as important a component to mammalian

morphological diversity as any anatomical feature.

To investigate the questions outlined above for mammals, I am obliged to use a

variety of instances and taxa throughout the class. However, in several cases I focus on

the Old World megabats (Chiroptera, Megachiroptera). These animals have a eastern

Gondwanaland distribution (Africa, India, southern Asia, Australia, and the associated

islands) and have speciated widely throughout this range. Although not all species'

genitals have been examined, the range of knowledge is comparable or superior to any

other mammalian group and the diversity of shape is much greater than that found in

primates and carnivorans. All species studied have bacula, and all the genera and many

species are readily identifiable by bacular form. Recent phylogenetic advances have

produced several possible evolutionary trees, providing more evolutionary context for

comparative study than other groups. Although reproductive behavior and physiology are

not as well understood for bats as for rodents, rodent phylogeny is especially problematic

and has only rarely been applied in comparative analysis of genital features (e.g.

Langtimm and Dewsbury 1991).

This dissertation follows a flow chart of evolutionary questions (Fig. 1). In

Chapter Two I show that it is not possible to identify a specific selective factor

responsible for the diversity of genital form, specifically bacula, from the current











Chapter Two
Can a specific selective factor be inferred for genital form?


Chapter Three


Might ontogenetic mechanisms explain the majority of bacular variation?


Chapter Four


Does variation in genital form follow taxon-level phylogeny?


Chapter Five


Does the phylogenetic perspective provide explanations for genital diversity?


,e %


Chapter Six
Qualitative Features

Y N


Have any specific selective factors
been eliminated or favored?

Y N


Chapter Seven
Quantitative Features

Y? N


Is body size a causal factor?

Y N


Figure 1. The experimental design and organization of the dissertation. Underlines
indicate the conclusions for each chapter.









literature, partly due to differing perspectives on the topic as it has been investigated.

Fortunately, developmental mechanisms for bacular variation may be understood through

a review of experimental studies of rodent ontogeny (Chapter Three), providing a

foundation for evolutionary questions. Homology remains a problematic concept for

evolutionary biologists, so how bacular composition and shape should be expected to

evolve remains mysterious as well, although several studies hint that morphogenetic field

theory applies to these features.

Chapter Four concerns whether bacular and genital form vary in tandem with

phylogenetic history. Another way of asking this is whether these anatomies provide

useful phylogenetic information. Bats, primates, and especially the colugo (flying lemur)

are of interest currently in light of controversies concerning the putative mammalian

grandorder Archonta, and soft tissue genital features have been included in the debate

(Smith and Madkour 1980, Pettigrew et al. 1991). Contrary to the view implied by

common practice, neither soft tissue nor bacular morphology contributes to resolving this

debate. Considering the features of the colugo and related taxa, mammalian genital form

varies both widely and discontinuously at the ordinal level. Using genital features to

resolve specific, single-taxon-level systematic controversies is not recommended.

Given that genital variation fails to mirror phylogeny, what among-species pattern

of variation, if any, does it present? This line of questioning yields unique evolutionary

insights. Chapters Five and Six concern variation in qualitative genital characters and

employ the techniques of Brooks and McClennan (1991) to map these characters onto

phylogenies. In Chapter Five, patterns are observed for cloacal features at the class level









within amniotes and for bacular presence at the ordinal level within mammals. They

suggest, respectively, that cloacal-genital tract separation may have evolved multiple

times within Mammalia, and that loss of the baculum is always preceded by specific

anatomical modifications. Chapter Six tests the hypothesis that male and female genital

morphological features are coevolved in the Megachiroptera.

Finally, Chapter Seven takes a phylogenetic approach to the long-standing

mammalogical tradition of comparing quantitative bacular features to body size. It

employs the technique of independent contrasts (Felsenstein 1985, Pagel 1992, Purvis

and Rambaut 1995), which permits quantitative features to be correlated in terms of their

evolutionary association. The study group includes all members of Megachiroptera for

which bacular data are available, and the features of interest include forearm length as an

indicator of body size, linear measurements of bacula, and curvilinear measures of bacula.

All scaling studies to date have employed the traditional comparative method, which

treats species as independent data points and are therefore flawed in their ability to

identify evolutionary patterns (Felsenstein 1985, Koehl 1996); the present study applies

independent contrasts to these features. Among the insights available are whether bacular

evolution is continuous or confined to specific nodes of evolutionary change, whether

bacular variation can be predicted by body size variation, and what bacular features may

be associated in their evolutionary origins with other features.














CHAPTER 2


PERSPECTIVES ON GENITAL DIFFERENTIATION

No eye may see dispassionately. There is no comprehension at a glance .... what
haunts the heart will, when it isfouna leap forward, blinding the eye and leaving
the main ofLife in darkness. (Peake 1967)


The Missing Overview

Organs that transfer sperm from male animal to female have evolved many times

and display a bewildering variety of origins and shapes (Eberhard 1985). This chapter

examines evolutionary explanations for this diversity. My central claim is that although

hypotheses concerning the evolution of external genitalia have been reviewed (Patterson

and Thaeler 1982, Eberhard 1985, Williams-Ashman 1990), the ideas summarized have

not established a shared understanding, and tests devised for one subdiscipline of biology

do not translate well into conclusions for others.

The outstanding question is: in what ways may genitals have evolved? This is

very distinct from the questions of how much they differ in shape, or what feature an

author thinks has been selected in a particular case. It is also different from merely listing

the hypotheses proposed so far (as did Eberhard, 1985). Until an experimenter proposes

a hypothesis such that it is truly an alternative to all others, the results generated will

continue to float in a conceptual vacuum. What is needed is something equivalent to the









energetics of estrous cycling, or the relationship of enamel to foodstuff consistency, or

the interaction of exchange membranes with air as opposed to water. Lacking this

biomechanical understanding, at the very least, the assumptions informing the existing

hypotheses should be explicit.

Why is a unified context for study so elusive? Eberhard's (1985) review describes

the hypotheses to date, and Edwards (1993) proposed that any hypothesis concerning

genital evolution was based on a framework of three assumptions, each of which having

several alternatives. Within the five major hypotheses that have been advanced to explain

the occurrence of genitalia that vary widely in shape between taxa, the corresponding

assumptions arose from the discipline of the hypotheses' origins.

1) Lock-and-key (insect version): male-female mechanical fit is limited in form

during speciation to prevent hybridization between incipient species.

2) Male versus female barriers: females are selected to develop barriers to

successful fertilization to control their mate choice, whereas males are selected to

overcome these barriers.

3) Female stimulation: females' capacity to be stimulated selects males to

stimulate, thus producing runaway selection in its own direction for a given

species.

4) Lock-and-key (mammal version): any feature of copulation, mechanical or

otherwise, may be emphasized or canalized during speciation to prevent

hybridization between incipient species.









5) Neutrality: genitalia, specifically the mammalian baculum, are not subject to

selection and their various forms are due mainly to pleiotropic effects.

All the hypotheses can be characterized by shared assumptions and distinctive ideas and

arranged in a Venn diagram (Fig. 2). From the early 1900s, entomologists have found it

easier than mammalogists to consider genitalia to be subject to selection. Hypotheses

appearing in either discipline over the last decades have varied in whether they consider

selection on genitalia to act on strictly mechanical features or physiological or behavioral

features and within or between taxa (Edwards 1993).

Because hypotheses about genitalia have varied widely in what they assume, the

same phenomena can be used to support a variety of explanations. Fundamentally

different hypotheses also share the same terms, such as "lock and key," but with

different meanings, which confuses matters further. A closer look at the histories of the

available hypotheses not only clarifies these conflicting assumptions but also reveals new

avenues of investigation.



Entomological Hypotheses

According to Mayr (1963), in 1844 Dufour proposed the earliest hypothesis

about how genitalia function in a pre-Darwinist, teleological context: insects are created

with mechanically incompatible genitalia to prevent them from miscegenating, such that

each species possesses its own copulatory lock and key. This hypothesis was later

converted into Darwinian terms by positing that hybrids are disadvantaged while their

parent














ENTOMOLOGY


Lock and key (Dufour 1844
reinterpreted)


Selective
Interspecific
Mechanical


Mechanical barriers (Lloyd 1979) Selective
Intraspecific
Biomechanical interaction (Mikkola 1992) Mechanical


Female-stimulus selection (Eberhard 1985) Selective
Intraspecific
Neurophysical










MAMMALOGY

Neutrality (Thornas/White/Burt)
Nonselective

Vaginal code [)iarnd 1970) Selective
Interspecific
Lock and key with tumblers (Dewsbury 1972, Neurophysical
Patterson 1983)

Selective
Intragender competition (Dewsbury 1978, Intraspecific
Edwards 1993) Neurophysical


Fig. 2. Historical trends in hypotheses regarding selection on animal genitalia.









populations are speciating, to justify the teleological idea that incipient species want to

differentiate (reviewed by Shapiro and Porter, 1989).

Newer entomological hypotheses shifted the selective focus to forces within, not

between, species; as Scudder (1979) noted, the isolating function of genitalia does not bear

close scrutiny on purely evolutionary grounds. Lloyd (1979) proposed the conflicting

interests of males and females regarding mate choice select for features of intromission

enabling a female to control the identity of her partners more effectively, or conversely,

enabling a male to overcome such barriers (Fig. 2), male versus female barriers. Lloyd's

(1979) hypothesis significantly modified the question to an intraspecific context: a

species does not have to be in contact with another for its genitalia to be subject to

selection. More recently, Mikkola (1992, 1993, 1994) demonstrated this outlook slightly

differently, using the term lock-and-key to describe the mutual selection between male

and female on biomechanical fit and interaction between genitalia (Fig. 2). This usage

concentrates on the mechanical aspect of lock-and-key and abandons its exclusionary role

altogether.

This intraspecific context was elaborated by Eberhard (1985), who extensively

reviewed the study of genitalia and attacked the mechanical lock-and-key hypothesis. He

proposed that the mechanism selected was not merely mechanical fit but a neural,

physiological response of the female to male anatomy (Fig. 2, female stimulation).

Specifically, male anatomy is selected for the extent to which it provokes such a

response. As females are not necessarily constrained in how stimulated they may be, in

each generation males continue to be so selected, and runaway differentiation ensues.









This sexual selection hypothesis was proposed wholly within the entomological

context, such that both mechanical fit and the interspecific context were treated as a single

invalid concept. Eberhard (1985) did not criticize neutralist interpretations of insect

genitalia beyond their mention and dismissal, because among entomologists these

concepts have not presented a significant challenge to the incumbent, lock-and-key.



Mammalogical Hypotheses

The history of thinking about how genitals have evolved in mammalogy has been

quite different and takes a different text as a starting point. Darwin (1859), citing Owen,

considered "organs of generation" unlikely targets for direct selection and thus more likely

to reflect phylogenetic groups. This view did not particularly influence entomologists,

but it became the central theme of the mammalogical tradition of this century, particularly

in regard to the baculum. Since the middle of the 19th century this bone has often figured

in taxonomic revisions. The evolutionary context for these studies remained unverbalized

until White (1953), who tentatively stated

Because the structures of the bacula are probably less affected by the action of the
external environment, they probably indicate relationships between groups of
species ... more clearly than the characteristics of skulls and skins. (p. 631.)

The view that because bacula were useful in taxonomy they were not subject to direct

selection is present in most papers concerning mammalian genitalia before and after

White's (1953) assessment. An influential paper by Burt (1960), as well as comments by

Mayr (1963), perpetuated the untested assertion of bacular neutrality. However,

selective advantage does not invalidate a feature's inclusion in systematic revisions (see









Chapter Four). Although Lidicker and Yang (1986) examined this issue in regard to

microtine phallic morphology, the contrary outlook is still widely held. Because the issue

remains unresolved, bacular variation has most often been used in a phenetic context, with

the exception of several studies on rodents, and genital soft-tissue features have only been

used as Hennigian characters relatively recently (Smith and Madkour 1980, Lidicker and

Yang 1986).

The mammalogical debate concerning genitalia, specifically the baculum, did not

concern how they were selected, but whether they were selected at all (Fig. 2, neutrality).

Although some mammalogists (Long and Jones 1966, Long and Frank 1968) did consider

the baculum to function in the service of species isolation, the nonselective interpretation

was directly challenged in a somewhat separate field, by researchers of mammalian

copulatory behavior.

Diamond (1970) proposed, in regard to copulatory behavior, that rodents may

have vaginal codes, that is, physiological requirements for successful fertilization, that

recognize only conspecific copulatory stimulus. Dewsbury (1972) classified mammalian

copulatory events to provide a potential language for the code. Dewsbury (1972, 1975)

also indicated that anatomical, neural, and physiological events interact during copulation

(Fig. 2, vaginal code). These ideas considered mammalian genitalia to be subject to direct

selection against miscegenation, but mechanical fit per se was de-emphasized.

However, m ammalogists continue to interpret selection on genitalia as an

interspecific phenomenon. Mammalogists' version of lock-and-key allows for a variety of

mechanisms and concentrates on its isolating, interspecifically distinct results. To them,









Eberhard's (1985) review of alternatives gave lock-and-key "short shrift" (B. D.

Patterson, pers. comm.) by primarily criticizing its mechanical nature and discounting its

isolating function only by association. Patterson and Thaeler (1982) reviewed and

analyzed bacular scaling and compared bacular-to-vaginal lengths in rodents to

demonstrate this view clearly: they reinterpreted lock-and-key in terms of tumblers, or

neural and physiological events prompted by mechanical events, in place of strictly

mechanical fit. They still considered these events to function in the service of species

isolation.

Exceptions to these major trends exist in both disciplines. Systematists studying

arthropods have certainly employed the nonselective model; for instance, nonselective

orthogenesis has been invoked to explain the elaborate structures of spider pedipalps

(Gertsch 1949). Conversely, mechanical barriers to interspecific mating have been

proposed for species of macaque monkeys (Fooden 1967). However, these and other

exceptions have not characterized explict investigation of genital evolution in either

discipline.

A Broader View

Neither the entomological nor the mammalogical perspective is necessarily wrong.

The failing is in accepting any one set of assumptions uncritically, which limits the

impact and meaning of experimental results on other workers' thinking. Studies showing

that areas of sympatry show no character displacement (Ware and Opell 1987), or that

genital morphology varies more interspecifically than intraspecifically (Zubaid and









Davison 1987, Dixson 1989), address only the within-species or between-species

question, not the adaptive ones.

Terminological drift also contributes to the problem. The term lock-and-key has

almost completely lost its isolation meaning for entomologists. Although Mikkola (1992,

1994) suggested that genital form in noctuid and geometrid moths acts as a prezygotic

isolating mechanism, he also specified that the selection in question acted entirely within

the species. However, for many mammalogists, the term now has two meanings, both

retaining the isolation function as primary: (1) mechanical fit as interspecific isolation

device, and (2) any copulatory event characteristic of a species, possibly but not

necessarily for species isolation. These meanings only share the arena of selection, not

the features selected.

To further complicate matters, there has been a split between workers on mammal

copulation, with the systematists and morphologists conforming mainly to the outlook

described above, and the behavioral experimenters and ecologists adopting the hypotheses

of Eberhard (1985).



Rodent copulatory behavior

Before 1985, studies of mammalian copulation searched in vain for a species-

exclusive, isolating mechanism for observed differences in copulatory behavior. Diamond

(1970) proposed the existence of a species-specific "vaginal code" in rodents, consisting

of copulatory events such as intromission and ejaculation frequencies, that would

function as a mechanism to prevent hybridization. The hypothesis was circumstantially









supported by Blandau's (1945) description of the events surrounding sperm transport

through the cervix of the rat, in that the caput penis and cervical lappets must interact

biomechanically for fertilization to occur. Experiments showing that ejaculation prior to

the appropriate number will not result in fertilization (Adler 1969) also supported the

possibility of such a code. Chester and Zucker (1970) suggest that the proximate cause of

this effect is the mechanical glans/cervix interaction, itself a function of the number of

intromissions.

Voles, like the laboratory rat, ovulate and implant in response to copulatory

stimulus (Davis et al. 1974, Gray et al. 1977 forM pennsylvanicus andM. montanus;

Milligan 1979 forM agrestis). Species of voles display a wide variation in penile and

bony anatomy (Hooper and Hart 1962), and also wide variation in copulatory behavior

(Gray and Dewsbury 1973, Dewsbury 1982), although the two sets of variables do not

form an easily-recognizable relationship.

Comparative studies in several species of voles sought to identify a vaginal code

for each species, such that other species' copulatory behavior that contradicted the code

would not result in ovulation and/or implantation. Studies on M montanus, M

pennsylvanicus, andM ochrogaster (Gray et al. 1977, Kenney et al. 1978) failed to do

so: nonconspecific copulatory behavior can induce ovulation; thus no exclusionary "code"

exists. Although differences in function between species' behavior were identifiable

(Dewsbury 1981), they could not be interpreted according to Diamond's (1970)

hypothesis.









After 1985, however, students of mammalian copulation have adopted the female-

choice sexual selection hypothesis uncritically. For example Harcout (1994) criticized

Edwards (1993) by citing sexual selection as an adequate theoretical framework for

studying genital diversity. Edwards (1994) replied that the real problem with this or any

other within-species selective mechanism is that it fails to explain why genitals may vary

widely between closely related species. The outstanding question regarding genital form

concerns the origins of its diversity. Even if sexual selection is precisely what affects

genital structure, then something about that selective milieu is changing when one form of

genitals or copulatory mode becomes another during speciation. Discontinuous variation

in copulatory phenomena across taxa may be due to (1) the very same selective forces as

operate within populations at all times, perhaps sexual selection, modified by founder

effects and bottlenecks; or (2) some within-population shift in what sort of copulatory

mechanics or chemistry are most successful. Whether or when either of these effects

occur remains an open question, not a reliable framework for hypothesizing at all

(Edwards 1994).

Another conceptual framework, however, renders the results of (for example)

comparative studies of microtine copulatory behavior more coherent. If the characteristic

copulatory events of a given species are the result of intraspecific selection, no need exists

to exclude another set of events from being effective. The anatomies, physiologies, and

behaviors of the animals can then be studied and interpreted as results of selection for

something else. The focus of the research is shifted to the "match" of anatomy and

physiology to behavior and the requirements for successful fertilization within species.









Given that within a species the structure-function complex occurring during copulation

"works," i.e. fertilization succeeds, the nature of bacular variation and development

becomes relevant to the investigation.

The vaginal code/tumblers hypothesis is easily converted to an intraspecific

context, which may explain why attempts to identify the vaginal codes of vole species

yielded identifiable but not exclusive copulatory modes (Davis et al. 1974, Gray et al.

1977, Kenney et al. 1978). In mammals as well as insects (Eberhard, 1985), anatomical

differences per se do not prevent nonconspecifics from copulating. The concept of

intraspecific selection on anatomical, physiological, and neural/behavioral features

presents at least as valid a context for hypotheses of genital evolution in mammals as the

interspecific context.



Toward plurality

Perhaps a more plural view toward genital evolution is possible, in that a single

mechanism does not necessarily have to apply to all animals, or even to a given lineage or

taxon. There may even be a continuum from the wholly interspecific, exclusionary model

to a completely intraspecific, internally selective one. Different groups of animals are

almost certainly subject to wholly different selective pressures on their mode of

copulation; similarly, a given species may be subject to more than one selective pressure

promoting genitalic differentiation.

Mammalogists may well consider de-emphasizing the interspecific assumptions of

their hypotheses, which, irrespective of mechanism, assumes a population becomes









differentiated while in contact with another. To produce such distinct genitalia apart from

most other features of the body, selection against hybrids must have been remarkably

consistent and severe. Furthermore, if the interspecific exclusion model is taken to its

extreme and the differences in genitalia actually facilitate the speciation process, then

much mammalian speciation must have been sympatric (see also Scudder 1979 and

references therein). This and other difficulties with lock-and-key, aside from the

mechanical aspect, have been reviewed for insects (Eberhard, 1985) and apply to

mammals as well.

A novel hypothesis for mammals was proposed by Edwards (1993):

Both male and female individuals of a species compete with conspecifics of the
same sex to improve their chances of fertilization; the actual feature selected varies
from species to species.

It differs from the sexual stimulation or any other strictly female-choice hypothesis in

that the feature in question directly affects fertilization success. Dewsbury (1988, see

also Estep and Dewsbury 1976) suggested a similar scenario in regard to copulatory

behavior, and it seems reasonable to regard the anatomy and behavior of copulation as a

functional unit.

Such selection has many other features to act upon in rodents besides caput penis

shape, such as female neural response for ovulation, female neural response for

implantation, location of sperm deposition, nature and placement of copulatory plug,

features of penile shaft and/or vaginal walls, although the caput penis shape may be

related to some of these as well.







23

Even if the precise, specific, and complete adaptive explanation for genital

morphology were accepted for a single species, it would not be sufficient to the purpose

of a shared understanding among biologists. In fact, effort spent to that end may in fact

be less valuable at present, so long as the overall, among-taxon pattern remains unknown.

It is that pattern which concerns the remainder of the dissertation.















CHAPTER 3


HOMOLOGY, DEVELOPMENT, AND BACULAR DIVERSITY

Here in the shapes of my body, leftover parts from the apes and monkeys ...
(Roberts 1994)


To understand the character evolution of genital anatomy, the mechanisms

producing the existing biological variation are of interest. Variation at its most basic is

produced by point-mutations in protein-encoding nucleotide sequences, but the one-gene-

one-enzyme approach to anatomical diversity has proven inadequate. The majority of

anatomical variation in a given taxon is probably due only to a small number of such

mutations, primarily in those areas of the genome concerned with the ontogeny of

structure (Gould 1977). This chapter addresses the developmental issues relevant to the

study of mammalian bacula.

First, there exists a contradiction at the heart of the current understanding of

developmental evolution and how it is to be applied to other biological issues, centering

on the exact meaning of homology. In this chapter, I provide new insights into why two

decades of debate have failed to produce a shared understanding of this term (Zelditch

1996).

Second, the current view (Hall 1994) of the three levels of variation in biological

form -- genetic, developmental, and anatomical -- provides a coherent model for radical









difference in anatomical shape between developmentally similar, closely related taxa. The

causal processes are almost certainly shared among all the taxa, but the results in a given

taxon are the net effect of a wide variety of conditional and epigenetic phenomena. This

view applies especially well to bacular variation (Williams-Ashman 1990).

Third, experimental insights from non-bat mammals suggests that the above view

is correct. Bacular shape varies widely among taxa, yet in the mammals studied it is also

invariant in terms of tissue composition and hormonal induction.

Finally, bacular shape may well be a model system for the study of evolutionary

constraint (sensu Maynard-Smith et al. 1985; see also Arthur 1988), itself a controversial

topic that requires clarification. Not only do megachiropteran bacula vary across taxa in

such a way that certain shapes are apparently never maintained (Edwards 1992), but

causes of such effects are most likely due to interactive, multiple-allele developmental

effects rather than point-mutations in genes coding for materials.



Homology and Synapomorphy

The current intellectual crisis surrounding the term homology was first recognized

by deBeer (1971), who pointed out that organ position, composition, and developmental

process have been confounded in assigning homology. With some frustration, especially

since he had addressed this issue several decades earlier (deBeer 1938), he concluded that

for practical purposes the term is undefined. All discussion of the matter since then has

illustrated his frustration: biologists are certain that it is a crucially important principle,

but wide disagreement persists regarding what it is (Hall 1994, Zelditch 1996).









Why is this so important? Evolution is rarely directly perceived, especially at

taxonomic levels above the species; all we have is evidence of its passing as illustrated by

features of organisms. Homology is intended to be the standard for tracking that sequence

of events, and Owen's (1843, cited in Panchen 1994) definition still stands:

[A] Homologue... the same organ in different animals under every variety of

form and function.

The conceptual controversies surrounding homology arise out of the words "same" and

"different." Sameness is often, if not always, taken to mean shared evolutionary origin

(Panchen 1994, Wagner 1996). But what are the criteria for identifying the right sort of

sameness? And how are those criteria recognized? If the last twenty years of debate has

shown anything, it is that different subdisciplines of biology have settled upon different

answers for these questions (Zelditch 1996).

Nearly all of the debate on these matters has focused on the levels of analysis,

which will be discussed later in this chapter. Less attention has been paid to the

problems that arise even if the level of analysis is given, or in other words, once it is

settled at what level to find similarity among organs, how should it be recognized?

Operatively, this also includes the question of its role in evolutionary studies.

There are two options, corresponding respectively to traditional developmental

biology and systematics: (1) to observe changes in organ systems across a phylogeny

(sensu Wagner's [1994] "structural identity"); and (2) to organize a phylogeny based on

changes in organ systems. Homology may be recognized either as the similarity in organ

composition, regardless of ancestry, or as shared ancestry, regardless of composition.









The last two decades' furious debate has surrounded this issue without ever quite

acknowledging it, and advocates of both views have emerged. First, many evolutionary

biologists are reasonably comfortable with Patterson's (1982; see also Patterson 1988,

Nelson 1994) claim that homology, as a term, may well be subsumed and replaced by the

term synapomorphy, which corresponds to the second option above (see Hall 1992b,

1994 for criticisms of this view). Second, pattern cladists have taken an entirely different

path to escape the conflict, namely eliminating the evolutionary context of homology

altogether. To these biologists, homology is strictly a means of earmarking characters as

appropriate to use in a tree, and any evolutionary inference regarding them or the

organisms should be done after the tree is made that is, long after homology has been

determined. Molecular evolutionary biologists use the same logic in a slightly different

application: to them, homology refers precisely to the congruence between base-pair

sequences in two different organisms (Patterson, 1988; see Hillis 1994 for review).

Again, they look for similarity between parts and call that in and of itself the homology,

completely unconcerned with, for example, the distinction between synapomorphy and

convergence. To biologists (like myself) more inclined to think that homology and

synapomorphy are interlinked terms, if not identical, this homology-first, evolution-

second approach looks deranged, but it actually represents an equally legitimate

interpretation of the basic conundrum.

Although homology as an abstract concept includes both meanings, recognizing

and analyzing homologous features requires taking sides, and biologists have a difficult

decision to make. In practice, homology either refers to observed similarity, which then









might or might not indicate shared ancestry, or it refers to shared ancestry, which may or

may not result in similarity of appearance. Currently using the same name for the two

approaches creates enough conceptual difficulty to hamper the advancement of research.

If developmental biology is truly to transform evolutionary thinking in the next century,

morphologists, systematists, and behavioral biologists will sooner or later have to call one

of these viewpoints homology, and the other will have to find a name of its own.

This dissertation adopts the first meaning for homology, that is, similarity. The

following section addresses the level and nature of homology as it applies to bacular

diversity, focusing on similarity of developmental processes. Whether similarities then

indicate synapomorphy is treated at the end of the chapter and in Chapter Four.



Developmental Levels

Bacular shape differences among taxa are best understood in developmental terms,

as opposed to allelic or strictly morphological distinctions. Even the most extreme

bacular diversity is probably due to synergistic effects of epigenetic phenomena

(Williams-Ashman 1990). This section explains my reasoning for this claim.

Three fundamental levels of organismal diversity are currently recognized (Hall

1994). At one extreme are genetic elements: base-pair composition, genetic sequences,

allelic interactions. At the other are elements of whole-organism adult morphology:

individual bones, their relationship to one another, size, and most other traditional

measurements. In between are the no less diverse substances and events referred to as the

epigenetic factors of development (Thomson 1988, Muller 1990, Hall 1992a):









topobiology, protein gradients and interactions, timing of events, and tissue-specific

induction. Specific epigenetic mechanisms include CAM-SAMs, matrix mediation, and

selective cell affinity (Edelman 1988); these are the processes which produce, for

example, heterochrony (Gould 1977, 1980, 1992).

Nelson (1978) proposed that homology, which he equated with common ancestry,

between adult organs should be determined by comparing similarities between

developmental processes essentially a reversal of Haeckel's biogenetic law, to say that

ontogenetic mechanisms determine (or provide evidence for) phylogeny. This view is

implicit in most anatomy textbooks and most anatomical approaches to systematics.

However, this outlook is undermined by one essential concept, recognized and

reiterated by all authors: that there is no 1:1 correspondence between the scale of change

on one of these levels to the scale of change on another. Small genetic changes can have

gross epigenetic or morphological consequences, dramatic genetic differences can be

meaningless at any other level, and so on. If "true homology" (ancestry) is to be

determined by a given organ or organ system, one or another level will have be chosen as

the one true indicator. Roth (1984, 1988) and Rieppel (1990) advocate choosing

epigenetic processes for this role. Alberch (1985), Hall (1992b), and Goodwin (1994), on

the other hand, prefer to keep homology assignments confined to a single level, but

acknowledge that all three levels are valid candidates. This debate is by no means over,

but its battle lines are acknowledged and authors who disagree are at least intelligible to

one another.









The useful thing about that lack of 1:1 correspondence, though, is the emergent

property of evolutionary buffering. If adult bacular shape, for example, is determined by

a few definite epigenetic interactions, then there is little need to analyze the genetic level

of diversity. Selection can work specifically on the genes for the morphogenetic

processes with no need for changes in, for example, alleles coding for presence or absence

of bone. The genes specifically coding for bone in the caput penis may well be all the

same in mammals the changes are occurring in the alleles that control the developmental

arena, and selection is acting (or not) on the diversity there. Edelman (1988) and Wagner

(1996, see also Muller and Wagner 1996) target this interaction between function,

development, and selection as the key to the diversity of organs, and Williams-Ashman

(1990, see also Williams-Ashman and Reddi 1991) suggests that bacula are an ideal

system for studying this interaction.



Bacular Developmental Mechanics

Adult bacular form is tremendously diverse among mammalian taxa (Burt 1960,

Patterson and Thaeler 1982). The diversity may be due to (1) high genetic diversity,

implying high rates of mutation; or (2) complex epigenetic interactions, leading to many

morphological outcomes due to the action of relatively few processes with

correspondingly few allelic bases. Which option is the case is not currently known, but

experimental work with rodents suggests the latter. The mechanics for rodent bacular

ontogeny are partly understood: several types of bone, several specific hormonal

induction mechanisms, and several tissue-induction mechanisms. A slight change in the









position or timing of any one of these factors will therefore produce a different form.

This section addresses consistent principles for bacular form underlying the variety in

both (1) composition and (2) inductive hormones.



Bacular composition

Bacular and baubellar components have multiple yet consistent developmental

origins in rats and mice, representing a variety of morphological results. The rodent

baculum is not a single bone, even in the mouse's structurally simple version, but is

divided into developmentally distinct proximal and distal portions that develop serially,

with a further distal pad of connective tissue (Fig. 3) (Ruth 1934, Glucksmann et al. 1976,

Murakami and Mizuno 1986). The proximal portion is itself divided into two. The

proximal part of the proximal portion is originally cartilaginous, growing as such until

eight days of age in the rat and subsequently ossifying endochondrally and continuing to

develop up to 100 days of age (Beresford and Clayton 1977a). This cartilage is distinct

from other late-ossifying cartilages such as the mandibular condyle in details of the

tissue's complement of alkaline phosphatase (Vilmann and Vilmann 1983). The distal

part of the proximal portion is endoblastemal as discovered by Ruth (1934) and detailed

by Glucksmann and Cherry (1972), Glucksmann et al. (1976), and Murakami and

Mizuno (1984). The distal portion is a fibrocartilage pad (Ruth 1934, Murakami and

Mizuno 1984); castrated male mice require enormous doses of testosterone proprionate

(TP) to induce this portion's development (Murakami 1986).



























Tunica
albuginea


EndDchondral Ehdoblast=l Calcified cartilage
bone bone


caput (glans)
penis


- Proximal Distal No


Fig. 3. Tissue composition of the rodent simplex baculum.


Corpora
cavernosa


Fibrous
connective
tissue


4-I*
penile
shaft









However, the relatively simple shaft-like baculum of rats and mice is a poor

representative of rodent bacular diversity. Rodent bacula appear in two types, simplex

and complex (Carleton 1980, Spotorno 1992). The latter is exemplified by the baculum of

Microtus, which is comprised of a proximal-distal shaft and three distal tines or digits.

The entire structure is contained within the glans, the proximal end of the shaft being

closely associated with the distal end of the corpora cavemosa and the digits closely

associated with various folds and mounds of the distal glans tissue (Hooper and Hart

1962). Each of the tines is apparently basal to a well-defined lobe of tissue. The distal

tines are not true bone at all, but rather cartilage that becomes calcified, beginning at

roughly one month of age and continuing throughout life in M montanus (Arata et al.

1965, see also Martin 1979). No length feature is age-dependent, but rugosity and

morphology definitely are. Most importantly, bacular variation is less a feature of

chronological age than of grade of physiological development. Similar but less complete

results are available for the golden hamster, in which there are four ossification centers

with distinct timing for each (Callery 1951, Dearden 1958).

To what degree the components of the complex baculum found in voles and

hamsters are homologous to those of the simplex version is unknown. Quite possibly the

distal cartilaginous portion of the rat or mouse baculum is homologous to the medial tine

of the complex baculum, but the distinct parts of the proximal portion remain a mystery.









Induction and maturation

Hormonal induction of bacular growth also appears to be reducible to a few

factors. Timing and receptivity to steroid and other hormones are apparently the

determining elements, although evidence is piecemeal and remains suggestive rather than

conclusive.

Noninterventional studies of the development of bacula are few in nondomestic

rodents and carnivorans; bats and primates have not been studied. Studies on

nondomestic animals are limited to aging studies in commercially important taxa, e.g. the

beaver (Friley 1949), species of seal (Scheffer 1950, Ryg et al. 1991, Miller, 1996), and

the mink (Elder 1951). All of these animals display changes in bacular morphology at

puberty.

Interventional studies of gonadal hormone influence on genital development are

also relatively rare for non-laboratory species. The longtailed weasel reaches sexual

maturity and full bacular elaboration at one year of age, in contrast to the rest of the

skeleton which matures at 3-4 months (Wright 1950). Castrated adults show no

regression of the baculum, whereas castrated infants never display bacular maturation;

testosterone proprionate (TP) replacement restores maturation in the latter. There is a

window of effect of replacement TP and growth hormone in intact beagles at 10 weeks of

age, after which neither hormone has an effect (Eleftheriou and Stanley 1963). Indian

palm squirrel bacular response is similar, with the exceptions that growth hormone has no

effect and that total replacement is not achieved by any dose of TP (Reddi and Prasad

1967). It is probably safe to say that the baculum develops in full at puberty as do many









other features of male maturation, mainly in response to testosterone and/or 5-alpha

dihydrotestosterone (DHT) (Baum 1979).

Studies on the laboratory rat and, to a lesser extent, the laboratory mouse

demonstrate the complexity of the role of gonadal hormones on bacular development

(Table 1). Bacular growth is restored in castrated animals by TP replacement (Turner et

al. 1941). Unlike the neuromuscular complex which expresses copulatory behavior,

baculum formation can only be restored by TP replacement to castrated neonate rats, as

opposed to adults or weanlings (Beach and Holz 1946). The mouse responds similarly to

both TP (to which the baculum was "more responsive") and dehydroepiandrosterone

(Howard 1959). Baculum restoration by TP is independent of hypophyseal hormones

(Thyberg and Lyons 1948), and TP and somatotrophin have a miffor effect: the former

restores the baculum to neonatally castrated rats and the latter has a synergistic but no

solitary effect, whereas the opposite occurs regarding skeletal bones (Lyons et al. 1950).

Non-interventional studies suggest even more complex interactions in more

complex bacula. In microtine rodents, the baculum is generally bonier in older animals,

and considerable variation exists in the extent of cartilage replacement in the digits

(Hamilton 1946, Dearden 1958, and Anderson 1960). There are seven separate centers of

ossification: one in the base of the shaft and two in each digit, the lateral digits being last

to become completely replaced (Dearden 1958). Anderson (1960) notes that the

baculum, unlike the testes, continues to be highly variable after animals reach full body

length; he attributes shaft variation (especially in the proximal end) to age and that of the












Table 1. (A) Summary of hormonal induction of bacular growth in rodents and
camivorans. (B) Results of tissue-replacement studies across genders of rats and
mice (Murakami and Mizuno 1984, Glucksmann and Cherry 1972, Yoshida and
Huggins 1980, Murakami 1986).


Hormone administered -


GH


somatotrophin


Tissue ,t

proximal and
distal
bone


distal
fibrocartilage
pad


replacement
during brief
window of
response


replacement
(massive
dose)


Procedure -


TP +
transplanted
male genital
tubercle


complete
miniature
baculum


TP +
transplanted
female
genital
tubercle


complete
baubellum


synergistic
effect


synergistic
effect


Subject


female
neonate


proximal
baculum


castrated
male


complete
baculum









digits to individual influences. All authors identify bacular variation to be an obstacle to

definite separation of taxa, with the sources of variation remaining unknown.

Other studies of androgen replacement in the laboratory rat generally demonstrate

the interaction between several genitalic and copulatory features and androgens. No one

hormonal factor can be identified as the cause of penile development, although epithelial

spines and papillae (Beach and Levinson 1950, Beach and Nucci 1970, Bloch and

Davidson 1971, Feder 1971, Hart 1973, Phoenix et al. 1976, Taylor et al. 1983a),

neuromuscular components of copulatory behavior (Beach and Levinson 1950), phallus

growth (Howard 1959 [for the mouse]), adrenal glands (Howard 1959 [for the mouse]),

and accessory glands (Hunt 1959, Beach and Nucci 1970, Feder 1971, Jannett 1978) can

all be reduced or eliminated by castration and induced to some extent by androgens. The

effects of androgens besides TP and antagonists show that the hormonal milieu is far from

simple. Testosterone phenylacetate has a lessened effect (Beach and Nucci 1970). DHT

restores seminal vesicles and penile papillae but not copulatory behavior, implying that

administered TP is only in part converted to DHT (Feder 1971). The antiandrogen

cyproterone has ambiguous effects based on administrative technique (Bloch and

Davidson 1971). Most interestingly, frequency of copulatory experience introduces a

confounding variable to the effects of androgen replacement, especially on penile spines

and musculature (Thomas and Neiman 1968, Folman and Dori 1969, Hunt 1969, Taylor

et al. 1983b).

Androgen dependency is also apparent in studies of intergender homology (Table

1). Treating a neonate female rat (which would normally develop a cartilaginous









baubellum) with pure testosterone induces a bony baubellum homologous to the proximal

portion of the baculum (Murakami and Mizuno 1984). Glucksmann and Cherry (1972)

induced a complete baculum in miniature (1/3 size) by transplanting male genital tubercles

into neonatally castrated female rats and administering TP. This procedure can only

succeed if the transplant occurs before seven days of age, using either TP or DHT

(Yoshida and Huggins 1980). The reverse procedure, culture of a baubellum anlage in a

male rat, succeeds with administration of TP (Murakami 1986). The androgen is not the

only causal agent, however; if a male rat's bacular anlage is transplanted elsewhere in the

female body it will not develop, with or without TP (Beresford and Clayton 1977), a

result corroborated by Murakami and Mizuno's (1986) demonstration that, in bacular

development, epithelium must be present to induce mesenchymal differentiation into

bone (see also review by Williams-Ashman, 1990).



Evolutionary Implications

Given the potential multiplicity of epigenetic processes producing bacular form,

the diversity of the bone itself, and the overall puzzle regarding homology, using genital

features for systematic purposes is problematic at best (see Chapter Four; see also

Scudder 1979 for a discussion of this issue regarding insect genitalia). The longstanding

tradition in mammalogy (Edwards 1992, 1993) has been to use bacula and other genital

features as taxonomic indicators and systematic characters. However, currently there is

no simple answer to the problem of how epigenetic causes of morphological variation

should be integrated with systematic procedures.









At worst, one might question using any feature as a systematic character until

homology, and how it should relate to building phylogenies, is better and more widely

understood. This idea may seem extreme, but McEdward's (pers. comm.) question, yet

to enter the published debate, is incisive:

What is a character? At what level are structures discrete evolutionary entities
and appropriate for analysis as homologs and synapomorphies?
Two issues emerge:
1) degrees of divergence in the characters (developmental and structural)
2) the hierarchical level of organization at which characters are defined and
analyzed
Elements of complex structures can have clear homologs in related clades but the
complex character might not. Alternatively, complex structures might be
homologs even if over time different elements come to constitute the components
of the structure.

Addressing this issue is beyond the scope of the present work, but it should be

recognized as perhaps the central conundrum facing evolutionary theory (see Williams et

al. 1990). As education in the diversity of developmental mechanisms and the

phylogenetic comparative method becomes more widespread in graduate training,

McEdward's questions may become more widely perceived and generate research to

address them (sensu Kuhn 1970).

I anticipate two avenues or issues: homoplasy and constraint. Homoplasy, the

bane of systematics, may result from similar development as well as similar selection.

Given two closely related populations, in each, development may provide similar

variations and selection may remove the same sorts of variants. Wake (1991) and Shubin

and Wake (1996) advocate concentrating on the former as the major element in producing

homoplasy, such that the processes at work in an organ's development be considered









more phylogenetically meaningful than those that select for a specific form. Until the

developmental mechanics of bacula are better understood, these factors cannot be

separated.

Constraint is at present a problematic term whose heuristic value is limited by a

variety of connotations (Maynard Smith et al. 1985). Here I employ it to indicate

variation that is either lost from an organism's developmental potential or is inaccessible

for biophysical reasons. For example, Edwards (1992) identifies the range of

morphological shape that apparently cannot be achieved in megabat bacula: relatively thin

and long combined with significant proximal bifurcation (Fig. 4). What is the evolutionary

significance of this effect? The developmental parameters evidently available for bat

bacula may themselves be the product of selection long past, or they may be subject to

current selection, or they may even be due to non-selective past phenomena. Calling the

apparent limits of megabat bacular variation a constraint is not yet warranted, and teasing

these effects apart by examining current variation is difficult and may not even be

possible. More important is to acknowledge that such parameters exist and to address

the directions and associations of specific features among taxa, within the parameters.

The phylogenetic history of developmental, biophysical, or selective change is

necessary for meaningful hypotheses concerning constraint. Although this dissertation

does not address constraint directly, the phylogenetic approach to bacular form that it

represents is intended as a precedent. Furthermore, as bacular variation may well

represent the action of a few epigenetic processes yielding a wide variety of adult forms,

























0.75-


OW)..




o D


0-





-0.25.





~A 9


0 S


'Irea


/


.3
0
S
S


Principal component 1
(relative width)






Fig. 4. Possible constraint on variation of bacular shape in 57 nominal species of
megachiropteran bat. Reproduced from Edwards (1992).







42


it may in the future serve as a case study for the role of development in constraining

morphology.















CHAPTER 4


GENITALS AND MAMMALIAN SYSTEMATICS

... nor is there one, but many ways of Coition, according to divers shapes and
different conformations. For some couple laterally or sidewise... some circularly
or by complication... some pronely... some mixtly.... This is the constant Law
of their Coition, this they observe and transgresse not. (Brown 1646, cited in
White 1954)


Brown's (1646) comments indicate that the behavior and anatomy of copulation

may be considered diagnostic, and in fact, faith in this concept underlies the widespread

use of genital characters in systematics, in plants as well as animals.

Genital and other copulatory features are almost certainly appropriate to include

as phylogenetic characters, but it should be remembered that phylogenetic trees include

clades that do not have taxonomic names. Adding characters to matrices or comparing

trees derived from different character sets will provide insight regarding somewhere in the

tree, but these methods may not help resolve a given taxonomic (i.e. clade-specific)

problem. Using genital features will not provide any special answer to this limitation. In

fact, at this time there is no consensus regarding what level, or what consistency of level

among taxa, that genital morphology should be expected to resolve.

This chapter concerns an instance of employing genital form as partial evidence in

resolving a specific taxonomic dispute. Its immediate purpose is destructive, that is, to









annull claims made by others and therefore to reduce the problem to its less-resolved

state. However, I believe such a purpose is constructive in the long run, especially in

terms of improving the standards and utility of research on genital form.



The Colugo Penis and the Archontan Question

Background

One of the most notorious current mammalogical debates concerns the

relationships between Primates and the two suborders of Chiroptera. Along with the less

speciose orders Dermoptera (the colugo, Cynocephalus volans) and Scandentia (the tree

shrew, Tupaia tupaia), these groups have often been classified together in the grandorder

Archonta (Smith 1980, Eisenberg 1981), but their phylogeny, questioned first by Smith

(1980) and subsequently seriously challenged (Pettigrew 1986), remains controversial.

The validity of Archonta, too, has been challenged, but that is beyond the scope of this

chapter.

The within-Archonta debate has concerned whether chiropterans are

monophyletic, in the context of the classic systematic puzzle: given one arrangement, one

set of character states is convergent, but given the other arrangement, another set is

convergent. A set of optic and neurological traits that may unite primates and megabats

(summary in Pettigrew 1991a, 1991b) is opposed by the host of features associated with

functional wings, which of course may unite both bat groups and receives strong support

from other mammalogists (e.g. Wible and Novacek 1988). Parsimony is confounded either

way, and neither side has been willing to accept a strict Hennigian solution of relying on









democratic parsimony (total evidence). Thus the debate turned to the validity of the

character sets: which is more convergent?

The fossil history of bats offers little help. True microbat fossils of about seven

species are known from North America and France (55 mya) and Messel, Germany (50

mya), and one megabat fossil species from Italy (35 mya), and no intermediate or

ancestral form is known at all, nor is the continent of origin currently determinable (Hill

and Smith 1984, Habersetzer et al. 1992). The next step was to turn to other characters of

extant taxa, in the hopes that overwhelming corroboration of either brain or wing

morphology would simply invalidate the other.

The decade of debate has produced many constructive results, and mammalian

systematics as a discipline would probably not have matured as quickly without such a

charismatic group at stake (see titles of Goodman 1991, Gibbon 1992) or the equally-

engrossing degree of acrimony (e.g. Simmons et al. 1991). Data sets for bats from nearly

every imaginable source have been added to the literature, such as blood sera proteins,

DNA sequences (Baker et al. 1991, Bailey et al. 1992), sequence data from mitochondrial

ribosomal RNA (Ammerman and Hillis 1992), and complex skull, neural, and limb

morphology (Thewissen and Babcock 1991, Wible and Novacek 1988). The phylogenetic

method has developed rapidly in the context of this debate (e.g. testing trees' robustness,

Ammerman and Hillis 1992), especially in terms of disseminating systematic methods to

general mammalogists. Presently most of the evidence corroborates the hypothesis of

microbat-megabat monophyly, although this conclusion relies more on consensus among

features rather than on certainty regarding their evolutionarily informative content.









Pettigrew (1991a) also uncritically includes Smith and Madkour's (1980)

suggestion that loss of accessory corpora cavernosa is synapomorphic for several

archontan orders, excluding microbats. Loss of a feature, in isolation, may be more

problematic (i.e. homoplasic) than its appearance. More importantly, in this case, the

earlier authors presented glans penis anatomy and other morphological features in terms

of many mammalian orders; Pettigrew (1991 a) was concerned only with Megachiroptera,

Microchiroptera, Dermoptera, and Primates.

The anatomy of the colugo and its role in the argument deserve re-examination.

Morphologically a near-perfect bat-primate intermediate, allowing for their interlimb as

opposed to interdigital gliding membranes, they are sometimes considered an ancestor to

megabats, and fossil evidence indicates that they may be more closely related to megabats

than primates (Beard 1990, Kay et al. 1990, Martin 1990, Pettigrew 1991a). To some

extent they may be considered a high-yield subject for investigation into the evolution of

winged mammalian form, and here I present the first account of their genital anatomy

since Smith and Madkour (1980), as well as its significance to the bat-primate debate.



Colugo penis anatomy

A more complete look at colugo genitalia calls into question Pettigrew's (1991a,

1991b) conclusions. Three penes (Field Museum of Natural History, 60132, 87394,

87401)were dissected from skin-preparations, prepared as alcoholics, and examined for

external features. Two specimens were placed in 2% potassium hydroxide (KOH) for

approximately 12 hours, at which time several drops of saturated Alizarin Red solution









were added. After approximately two hours they were placed into 2% KOH again until

the tissues began to clear. They were transferred to 50% glycerin for 24 hours and then

to 100% glycerin; in this condition internal penis features were apparent.

Cynocephalus volans. External features (Fig. 5): retractile sheath absent, prepuce

present, skin on outer shaft covered with hair up to the beginning of the prepuce over the

glans, shaft and glans extremely rigid (possibly due to collagenous fibers); caput penis

constructed of solid, non-flaccid tissue, divided into one central lobe terminating in the

urethral opening extending distally and two lateral lobes further subdivided extending

either distally or distolaterally, all lobes moderately covered with small nubs; urethral

opening is a rigid lateral slit with a ventral lappet. Internal features (Fig. 6): baculum

absent, urethral opening moderately wide and terminating through the central lobe, true

corpora cavernosa extending into glans penis dorsal to urethra.



Phylogenetic comparisons

Absence of accessory corpora cavernosa is shared by megabats and primates, but

it does not unite them exclusively unless microbats are the only outgroup. Because the

colugo also lacks accessory corpora cavernosa, when all four groups are considered with

Phylogenetic Analysis Using Parsimony (PAUP; Swofford 1990), the feature becomes

phylogenetically uninformative; in fact, no genital character is shared by two taxa (Fig. 7).

Bacula are absent only in the colugo and penile rigidity is present only in the colugo.

Pettigrew's (1991a) primary error is in limiting his analysis only to the four





















A


B




C


DISTAL


L


DORSAL VENTRAL






Fig. 5. External features of Cynocephalus volans from specimen reconstituted from
skin preparation and preserved in alcohol (FMNH 87394). A = glans penis, B =
reflected prepuce, C = shaft of penis. Shaded areas on glans indicate rough skin.

















5 cm


2 cm


VENTRAL


LATERAL


60132


VENTRAL

87401





Fig. 6. Glans penes of Cynocephalus volans (FMNH 60132, 87401) with prepuce
retracted to expose glans, following clearing with 2% KOH. A = glans penis, B =
reflected prepuce, C = shaft of penis.


A




















wings
I


t
loss of accessory
corpora cavernosa


optic/neural
features


Q- Microchiroptera

Dermoptera
S,
ity
Primates

-- Megachiroptera
t
wings


Fig. 7. Distribution of putative archontan synapomorphies (closed
circles) contributing to bat diphyly and autapomorphic or reversed
features (open circles) (adapted from Smith and Madkour 1980,
Pettigrew 1991).









orders/suborders; the secondary error is in failing to perceive the relevant clades of penis

evolution to be different from the taxonomic clades.

Two genital features, bacular presence and penile rigidity, were added to the

matrix of 52 morphological characters for nine mammalian orders and subordinal taxa

presented by Novacek (1994) (Table 2), and results with and without these characters

were compared with PAUP (Swofford 1990). All new trees were most-parsimonious.

Bootstrap percentages for each branch of the original bootstrap 50% majority-rule

consensus tree (1,000 replicates) were not substantially changed by the addition of the

genital features (Fig. 8). The tree including the genital features is partly homoplasic

(consistency index 0.79), based on Novacek's (1994) characters 37-46, including his three

genital features, but also on both of the added genital features. All genital features

required two or three steps to agree with the tree (Table 3). The genital features' degree

of homoplasy exceeds that of the non-genital features by far, only two of which have a

C.I. of 0.33.



Discussion

Genital features are phylogenetically uninformative in the four-taxon context

presented by Pettigrew (1991a). The putative genital synapomorphy among primates

and megabats is not corroborative with that suggested by optic/neural features, as the

colugo lacks wings, accessory corpora cavernosa, and the optic/neural apomorphies. If

Archonta is a valid grandorder, an assumption not seriously challenged either by Smith

and Madkour (1980) or by Pettigrew (1991 a), the accessory corpora cavernosa and the










Table 2. Characters added to Novacek's (1994) morphological matrix for
mammals. Lack of information is indicated by (?).



Character Code: 0 Code: 1

Baculum absent present

Penile absent present
rigidity

Accessory present absent
corpora
cavernosa



Taxon Code

Edentata 00?

Anthropoidea 101

Strepsirhini 101

Dermoptera 011

Scandentia 001

Artiodactyla 011

Microchiroptera 100

Megachiroptera 101

Rodentia 100









Table 3. Character step transitions for three genital features based on most-parsimonious tree including 54 morphological features
(asterisk indicates character is from Novacek 1994). Consistency indices of non-genital features (Novacek 1994) presented for
comparative purposes.


(:HARACTER

Bacular presence


# STEPS INCLUDED


CONSISTENCY INDEX


0.33


Penile rigidity

* Pendulous penis

* Distally expanded,
vascular corpus
spongiosum
* Absence of accessory
corpora cavernosa

* 2 non-genital characters

* 2 non-genital characters

* 5 non-genital characters

* 40 non-genital characters


0.33


0.33


0.667


TAXA


Rodentia (gain), Primates
(gain), Chiroptera (secondary
loss)
Dermoptera (gain),
Artiodactyla (gain)

Archonta (gain)

Archonta (gain),
Scandentia (secondary loss),
Microchiroptera (secondary
loss)
Archonta (gain),
Microchiroptera (secondary
loss)

(various)

(various)

(various)


1 1.0


(various)

















Edentata

88 Anthropoid
81 0Strepsirhine

97 8Scandentia

95 9Dermoptera
19 9
Microchiroptera
100 Megachiroptera

Artiodactyla

Rodentia








Figure 8. Bootstrap 50% majority-rule consensus tree of mammalian groups generated
from 52 morphological features from Novacek (1994) and two added genital features.
Topology does not differ from the original tree. Numbers above the branch lines indicate
bootstrap percentages for Novacek's (1994) data and those below indicate those for the
data including the genital features.









optic/neural features are not supporting megabat-primate monophyly at the same node.

The more inclusive view of mammalian ordinal phylogeny also suggests that

bacular presence, penile rigidity, accessory corpora cavernosa absence, and expanded

glans penis are notably homoplasic across the orders (C.I. range 0.33 0.5). The only

genital feature with an unambiguous role is the derived pendulous penis (C.I. = 1.0),

diagnostic of classic Archonta.

It would be especially helpful if copulatory anatomy and behavior, as we

currently quantify them, were to evolve in such a way as to trace the history of

reproductive isolation, so that they would provide a literal, synapomorphic map of the

instances of speciation. Unfortunately, this rosy picture is not the case. The multitude of

features comprising copulatory diversity do not evolve in tandem with one another, and

some of them may be notably homoplasic. Even more dismaying, shifts in genital form

rarely coincide with the shifts in ecomorphological features usually employed to define

higher taxa. It is as if there were two cladistic stories occurring simultaneously but

somewhat out of synchrony, confused further by quarrelsome and sometimes vague plot

elements in each. Further work on this topic should include robust tests of statistical

congruence for mammalian genitals at a variety of taxonomic levels, which, as long as

genital information is employed as casually as in Pettigrew (1991 a), is far from likely.










Systematics and Phylogenetic Truth

Systematic protocols

Three concerns dominate the modem field of systematics: bringing taxonomy and

systematics methodologies together into a mutually supportive whole (Patterson 1982),

generating phylogenies with sufficient rigor to withstand testing (e.g. Faith and Cranston

1992), and standardizing the means by which these phylogenies will serve as the unifying

theme for the modem comparative method (Wilson 1989). This dissertation primarily

addresses or represents the third concern, but the second is also relevant to the study of

genital variation.

Several mammalian phylogenies have been generated utilizing genital and

especially bacular form, for carnivorans and marsupials (e.g. Long 1969, Long and

Cronkite 1970, Hrabe 1972, Sutton and Nadler 1974, Patton 1983, Tumlison and

McDaniel 1983, Maser and Toweill 1984, Izor and Peterson 1985), and to some extent

rodents and bats as well (e.g. Jannett 1976, Williams et al. 1980, Nader and Hoffmeister

1983, Patterson 1984, Burns et al. 1985, Hill and Harrison 1987, Yensen 1991, Simson

1993; see also Hood and Smith 1982 for use of female characters; see Edwards 1992 for

review).

As long as such research limits itself to resolving phylogeny, all is well.

Classically, the Hennigian phylogenetic methodology is intended to generate

parsimonious trees from a matrix of character states, and the nodes of the resulting tree

represent instances of speciation. Such a method is a great boon to the systematist faced

with dozens of taxa, dozens of characters, and a bewildering array of variation, to whom









any tree will do as long as it conforms with a sensible algorithm and proves to be the

most robust version. Mammalian ordinal phylogeny, for example, is illuminated by

combining a wide variety of character sets, generating consensus trees, and testing trees to

determine which are sensitive to which features' presence.

A controversy such as the bat-monophyly debate is entirely a different endeavor.

The competing hypotheses do not correspond to a single tree apiece but rather to any tree

with bats monophyletic, as opposed to any tree with bats diphyletic. Thus two

character sets may generate very different evolutionary stories, yet according to this view

support the same conclusion. Or, as in the case of genital form, a character set may well

contribute to the phylogeny, yet not to the taxon-specific question at hand. Hennigian

methods' utility in such a debate become misleading when casually applied, as

demonstrated by Pettigrew's (1991a) claim that genital morphology supports bat

diphyly.

Another potential confounding issue is the role of adaptation. A very few papers

(Ewer 1973, Mondolfi 1983, Levenson and Hoffman 1984, Lidicker and Yang 1986)

acknowledge that bacular form, for instance, cannot be used as a gauge of phylogenetic

distance, and suggest that a better understanding of genital form in biomechanical or

adaptive terms would improve our systematics. However, this suggestion has nowhere to

go. There currently is no consensus on whether the adaptive value of a feature makes it

less or more appropriate as a character for cladistic purposes.









Positivism

Positivism is the most formal and explicit of science's claim to approach objective

truth. The principle of this method is to eliminate the false (the "negative") from

consideration, usually on the basis of probability, explicitly to add, piece by piece, quanta

of knowledge to an ever-growing store (Popper 1985). Modem systematists are sensitive

to the criticism that their discipline is not positivist, or hypothetico-deductive. M. M.

Miyamoto (pers. comm.) suggests that the less-robust trees "rejected" by a phylogenetic

algorithm are technically tested in the production of the more-robust trees; however,

techniques to test character sets' relative values remain an active topic for debate. Like

ecologists of the 1970s faced with accusations that their discipline was nothing but data

looking for a science (see Quinn and Dunham 1983 for review), systematists of the 1990s

test their trees to the strictest dictates of the hypothetico-deductive method in an effort

to be truly scientific. And again, like those ecologists (review in Hurlbert 1984), they

may be falling into the trap of testing unnecessarily.

At the grandest level, this insistence on a strict positivist approach might be

reconsidered. Science, apparently, may not be as scientific as it looks. Latour and

Woolgar (1986) demonstrated that biomedical researchers strive to conform to a positivist

image despite its minor role in their actual intellectual endeavors, and Medawar (1963)

cogently criticized the common practice of organizing scientific papers as if they were

journalistic reports of a pristine Scientific Method. There even exists serious controversy

as to whether any science conforms to a hypothesis-testing model (Dickson 1997), and

the very principles of natural selection have been cited as a grand tautology (Peters 1976









and references therein). And if Kuhn (1970) is even partly correct that a given era

(culture) can only examine a limited set of scientific questions, then the avowed

positivistic goal of establishing an unshakeable edifice of truth is simply impossible.

Even in the worst-case scenarios, in which positivism is an unattainable goal either

for science as a whole or only for systematics, all is not lost. Woodward and Goodstein

(1996) offer a perspective on scientific activity that reveals a healthy form of positivism

to which the discipline might aspire: falsification am studies, especially those of

competing researchers, rather than within them. According to this view, researchers

perform studies that confirm, not falsify, their own beliefs, and the testing and rejection

of hypotheses occur over a series of publications from more than one and possibly many

workers. Therefore science is positivist although scientists and their individual studies or

bodies of work are not. Perhaps systematics is best understood from this perspective,

and its crucial role for the comparative method (see Chapter Five) therefore supported.















CHAPTER 5

THE PHYLOGENETIC APPROACH TO GENITAL CHARACTER
EVOLUTION: QUALITATIVE FEATURES


Don't know much about history,
Don't know much about biology (Sam Cooke)


This chapter is the first of two to address how qualitative features of genitalia

have evolved. It includes (1) a partial retrospective on the comparative method and why

a phylogenetic perspective is essential to the questions raised by this dissertation, and (2)

phylogenetic analyses of two genital features, the amniote cloaca and the loss of bacula in

mammals.



The Phylogenetic Comparative Method

The practice of the comparative method has greatly changed in the last five years,

the key difference being the inclusion of systematics. The classical comparative method,

when focused on interspecific studies, was rooted in the search for optimality in

biological systems: given an environmental circumstance, what works best? If organisms

independently evolve similar solutions to similar circumstances, we have evidence for

adaptive origins for the features producing the solutions (Krebs and Davies 1987,

Dewsbury 1990, Harvey and Pagel 1991). Comparing species' features directly is indeed









a very powerful method and represents an important aspect of comparative biology, but

as an investigation of evolutionary process, without phylogeny it is not complete (Harvey

and Pagel 1991, Koehl 1996).

The classical comparative method associates features as they appear in individuals

or groups, with little distinction between within-taxa and among-taxa variation. One goal

is to identify limits to biological variation, whether in terms of environments in which

certain features cannot evolve or biophysical constraints on performance. In practice,

when more than one taxon is included, especially if they are analyzed as a group, the

limits in question, for example the surface-area-to-volume ratio, are assumed to operate

on all of them. Depending on the limit, this sort of comparison is taxonomically

restricted, in that it works best for organisms that are enough alike developmentally to be

adapted in similar ways. The only explicitly evolutionary result detectable by this

method is convergence, or more accurately, parallelism.

The role played by phylogenetic relationships between taxa has not always been

clear. Krebs and Davies (1987) and Dewsbury (1990) suggest confining the taxa per

study to a shared-ancestry group, e.g. species within a genus or family, apparently to

maximize the chance that similar selection will produce consistent results. Such a

practice would thus be an explicit hunt for parallelism. Conversely, Alcock (1984a)

suggests testing across extremely diverse groups, which implies that the effect being

scored should probably be possible for a wide variety of biological systems and

represents a hunt for true convergence.









Not all comparative studies are explicitly evolutionary. Schmidt-Nielsen's (1984)

discussion of body size and scaling avoids any discussion of evolution except in terms of

common solutions to universal biophysical concerns, which again, translated into

selective terms, means convergence. In this sort of study, comparing multiple taxa is

essentially a means to increase sample size across a wide enough range to perceive the

physical limit in question, and the phylogenetic jump represented by speciation is not

relevant. Koehl (1996) defends this point of view given that the targets of investigation

are proximate mechanisms, but also states that evolutionary hypotheses regarding

comparative data are not tenable unless they are phylogenetically consistent. Although

this may seem elementary, the three elements -- comparative data, evolutionary

hypothesis, phylogenetic perspective are not always present, for instance, in

Schwagmeyer's (1990) analysis of sciurid reproductive competition, which, having

established tremendous diversity in a closely-related set of species, suggests the best

method for explaining it is to investigate mechanisms. Beach (1950) warned against this

trend in comparative psychology, fearing that behavioral research would become over-

reductionist and lose sight of its driving questions. If comparative biologists were not

interested in evolutionary issues, this would be acceptable, but this is clearly not the case.

Examples include studies of the origins of mammalian endothermy (McNab 1978),

causes of metabolic rate differentiation in extant taxa (McNab 1992), the range of bacular

variation in rodents (Patterson and Thaeler 1982) and megachiropteran bats (Edwards

1992), and mating strategy in orb-weaving spiders (Christenson 1990).









When evolutionary process is indeed the explicit goal of the study, the classical

comparative method's most serious limitation appears: confoundment by

symplesiomorphy (shared retained primitive characters). Felsenstein (1985) identified

this problem as one of statistical independence, in that features from taxa belonging to a

nested phylogenetic hierarchy cannot be treated as independent data points and that

inferences from such data will be flawed (see also Brooks and McClennan 1991). The

problem is analogous to that in experimental design: a set of such data may be considered

to include points of pseudoreplication; to reduce the points from the taxa themselves to

the nodes of differentiation on the branching hierarchy, almost certainly reducing the

number of points, actually clarifies the data from a confounded state.

Adding phylogeny to the comparative method not only solves the

symplesiomorphy problem, but it also expands the scope of what evolutionary questions

may be asked. In the last five years, the intellectual emphasis of the comparative method

has shifted, from observing (and being limited to) the same effect on widely separated

animals to comparing before and after effects within a lineage of related animals. Instead

of analyzing instances of a single evolutionary pattern, convergence, the method

investigates, for a given set of organisms, what evolutionary process is most likely to

have occurred among them.

The phylogenetic method is especially useful in dealing with a group of features

that appear in a variety of combinations among taxa. For example, Lauder (1981, 1990)

has shown that the complex morphology of cichlid fish jaws can be interpreted









adaptively, but in a shifting mosaic of options across closely-related taxa instead of a

one-time origin in widely-separate taxa.



History and adaptation

Discussion concerning phylogenetic comparisons was paralleled by another about

adaptive tenninology, which, although ultimately not proving its instigators (Gould and

Lewontin 1979, Gould and Vrba 1982) wholly correct, prompted others to reexamine

assumptions about the role of adaptation in the origin of extant diversity. The issue was

procedural: how may direct selective effect be detected by comparing features across a

range of taxa? And specifically, what constitutes an appropriate null hypothesis?

Evolutionary theory began to focus on neutral characters and a nebulous concept of

constraint, and the discussion began to concern phylogenetic evidence rather than the

principles of population genetics.

Debate during the rapid development of scientific ideas may sometimes be low-

yield. One of the more problematic examples from this debate concerned genitalia,

specifically the human clitoris. Gould (1987a, 1987b) and Alcock (1987) disagreed

whether this structure, as well as male nipples, represents an adaptation. The former

suggested that the strong selection on male penis form was solely responsible for its

early, pre-differentiation development in the female with no special selection necessary

on clitoral form itself. The latter responded that the clitoris is "functional," which

presumably means that it is composed of living, integrated tissue and is therefore present

only due to direct selection. The argument was seen as an example of conflicting levels









of analysis (Sherman 1989, Mitchell 1992), which misses the fact that both authors were

simply wrong. Gould's point is incorrect because the presence of a developmental

homologue, however directly acted upon by selection, does not suggest that the structure

is not subject to selection; Alcock's is incorrect because functional in an organic sense

does not suggest that selection has occurred. When otherwise-outstanding biologists

generate this level of discussion, the problem rests not in knowledge or competence, but

rather in how to ask the question appropriately. Significantly, although the topic at hand

concerned evolutionary origins, neither author suggested examining clitoral presence,

structure, or function in nonhuman outgroups.

Another problematic term from these discussions is "history," variously re-stated

as phylogenetic component or phylogenetic constraint and suggested as an appropriate

null hypothesis for studies of adaptive behaviors (Gould and Lewontin 1979). By this

view, historical or phylogenetic effect implies non-selective effect (e.g. Bock 1977). This

is emphatically not the outlook adopted by the present study. Here, history in the

biological sense is defined as the variation made unavailable to a lineage, of however

many clades, over the course of time. Existing variation, then, represents only a fraction

of that produced by mutation and recombination from the beginning of the lineage to the

present. When the traits in question include the range of operation of epigenetic

developmental factors, the term "developmental constraint" is appropriate. This is very

different from the concept of biomechanical or physical constraints (Maynard Smith et al.

1985), nor is it related to Alcock's (1984b) concept of constraint as a lack of individual

flexibility.









My view of history is not as an alternative to adaptation. Some of the history in a

lineage, that is, lost or currently unexpressed variation, has been due to natural selection,

which may or may not be operating at all or in the same way at present. To consider the

evolutionary effects on genital form, the history of change, of whatever sort, must be

considered, and that means beginning with a phylogeny (Brooks and McClennan 1991,

review in Losos and Miles 1994). The differences between adaptation and exaptation,

history and selection, and constraint and selection are not relevant to the issue and are

now beginning to be recognized as obfuscating rather than constructive distinctions

(Sanchez-Villagra 1996). The correct phrase, rather than history versus adaptation, is "the

history 2f adaptive and other change."

It is inaccurate to think of phylogeny as some mysterious causative entity similar

to food preferences, body size, performance values, metabolic rate, biogeography, role in

the ecological community, skull shape, and so on. Instead, phylogeny narrates the

shifting mosaic of the species- or group-specific values of these things. In asking

evolutionary questions about features' presence or magnitudes, phylogeny cannot be

factored out but rather must be included to dictate how the values are summarized for

comparison.



Phylogenetic Analyses

Phylogenies have become central to much comparative work of the last five years.

As the revolution in systematic methods became incorporated into graduate education

and thereby into academia at large (Wilson 1989), evolutionary trees began to preface









comparative papers routinely, beginning not surprisingly with functional morphology

(review in Losos and Miles 1994) and now evident in ethology (Edwards and Naem

1993, Clayton and Cotgreave 1994, Cooper 1995) and development (e.g. McEdward and

Janies 1993, David and Laurin 1996). Langtimm and Dewsbury (1991) provided the first

fully phylogenetic study of copulatory behavior and anatomy.

Brooks and McClennan (1991) present three possible causal relationships

between two sets of characters across taxa (Fig. 9): one may select for the other, vice

versa, or both may be responses to a third feature. Failure to accord with the first two

falsifies the hypothesis of coevolution ("coadaptation"); failure to accord with all three

falsifies the hypothesis of any causal relationship between the features at all. The

preliminary studies that follow further demonstrate the unique insights regarding genital

evolution to be derived from this approach.



The mammalian cloaca

The posterior orifices of the amniote body are associated in most cases by a

cloacal arrangement, with the anal, urinary, and reproductive tracts emerging into a

chamber which itself has one opening from the animal's body. In males, the seminal

tract terminus often includes a penis. This basic arrangement has been variably modified

by different vertebrate classes or left relatively unchanged, as in chelonians, crocodilians,

primitive mammals, and primitive birds (Fig. 10). Derived birds and squamates,

including the tuatara (Sphenodon) have apparently undergone an independent loss of the

cloacal penis in males, and in the latter group a replacement or reversal of function















A B


A B


Fig. 9. Potential sequence of events for coadapted traits. A) Trait 2
represents a potential adaptation to conditions imposed by Trait 1, B)
Trait 1 represents a potential adaptation to conditions imposed by Trait 2,
C) Traits 1 and 2 potentially represent responses to a third condition, not
necessarily to one another. After Brooks and McClennan (1991).


A B















Chelonia




Mammalia





Squamata
(inc. Sphenodon)


Crocodilia


Archosaurs and
relatives


ancestral
Aves


derived Ayes


Fig. 10. Modifications of male amniote cloacal anatomy. Asterisk indicates cloacal anatomy
including penis. Derived mammal and bird branches may indicate more than one
evolutionary origin.









evidenced by the hemipenes, which are not cloacal. A host of probably unanswerable

questions is raised by these phenomena, including what sort of intermediate devices were

included in extinct squamate and protosquamate taxa, as well as some that may lead to

future research, such as what reproductive features accompany penile loss in birds and

hemibacular presence in varanid lizards.

Derived mammals, uniquely among amniotes (with the possible exceptions of

archosaurs and mammal-like reptiles, who must remain unknown), have become non-

cloacal by separating the anal tract from the others with external perineal tissue. The

position of the urinary tract in cloacal mammals, whether it is contained in the penis, has

not been investigated. The cloacal mammals include the pika, Ochotonaprinceps (Duke

1951); mouse opossums, all members of the Microbiotheriidae (Hershkovitz 1992); and

several insectivorans and the prototherians (Nowak and Paradiso 1983). This distribution

raises several questions and suggests at least two origins of the non-cloacal arrangement,

one in Marsupialia and the other in Eutheria (Fig. 11).

First, is the penis of placental mammals itself a derived feature, or is it

symplesiomorphic with the cloacal penis of the rest of the amniotes? D. Kelly (pers.

comm.) considers the tissue derivations of the monotreme penis to be considerably

different from that of the viviparous mammals, but acknowledges that the developmental

processes may be homologous. Second, are cloacal eutherians long-lasting plesiomorphs

or do they represent instances of reversal? S. Hidden (pers. comm.) suggests that all the

eutherian cloacal forms are best considered reversals. This question is obscured to some

extent by assertions that eutherian mammals have nothing so primitively reptilian as a












prototheuia

ancestral marsupials

derived marsupials
ancestral xeaarthrans

derived xenartbrans
pika

rabbits and hares
ancestral insectivorans

derived insectivorans


prototheria

ancestral marsupials

derived marsupials
ancestral xenarthrans

derived xenarthrans
pika

rabbits and hares
ancestral insectivorans

derived insectivorans


Fig. 11. Alternative models for the evolution of cloacal anatomy in mammals.
A) Two appearances of the perineum (closed circles), with multiple reversals to
cloacal form (open circles) in the Eutheria. B) Multiple appearances of the
perineum, with eutherian cloacae as symplesiomorphies.









true cloaca (Smith and Madkour 1980) as well as no clear documentation regarding

cloacal anatomy and its distinction from urogenital sinus in several groups, such as

xenarthrans, Insectivora sensu lato, capybaras, and beavers, the last of which is

referenced only in a popular-audience book (Parsons 1989).

As mammalian ordinal phylogeny has become more controversial in recent years

than ever before (Benton 1988, Miyamoto and Goodman 1986, Novacek 1982, Shoshani

1986), there is probably little hope that the cloacal question will be resolved easily. But

these evolutionary and adaptive mysteries can only be asked in terms of specific

phylogenetic shifts. Gould and Vrba's (1982) concerns about the role of the history of

selection are certainly borne out in this case, although more in terms of how it acts at

different nodes on a tree rather than along an anagenetic lineage.



Bacular loss in carnivorans and primates

Bacula are present only in the mammalian orders Carnivora, Primates, Chiroptera,

and Rodentia, which implies the bone is not primitive for mammals. Whether it

represents a synapomorphy for these orders is unknown. In ungulates, marsupials, and all

the other mammals, it is unknown whether at any time bacular presence was selected

against or it never arose. Within the orders which do have bacula, they are almost

universally present, excepting only in the hyena (Crocuta crocuta), the human (Homo

sapiens), the spider monkey (genus Ateles ) and multiple members of Microchiroptera.

Bacular loss presents a rare biological event that may prove insightful to our evolutionary

understanding of genital form and even conceivably relevant to understanding our own









species. However, no hypothesis concerning the evolutionary significance of bacular loss

has been advanced, as bacular presence is usually considered only in terms of

diagnostics. Bacular presence might be proposed as the dependent variable and a wide

variety of causal predictors might be tested one by one: mating system body size, penis

size and so on. But applying phylogenetic thinking not only diminishes the number of

species appropriate to examine but also provides insights otherwise unavailable regarding

what independent factor to propose.

The pattern of characters accompanying the evolution of bacular loss in the hyena

and the human is the same (Fig. 12): an outgroup with a robust baculum and, in at least

some species, complex erectile mechanisms, and a sister group with a small, internal

baculum and relatively simple erectile mechanisms (e.g. loss or reduction of the

accessory corpora cavemosa). Furthermore, in both species lacking bacula, the penis is

larger relative to body size than in its sister groups. The spider monkey (not shown) is

harder to interpret because cebid phylogeny remains controversial, but in the other large

cebids Lagothrix, Alouatta and Brachyteles, the baculum is small, and, as in the hyena

(Racey and Skinner 1979), the clitoris in Ateles is isomorphic with the penis (Eisenberg

1973, 1976). The pattern would include two steps: first, a general simplification of penis

form, including reduction or loss of accessory corpora, a generally small penis, and the

baculum contributing little or nothing to penis shape; then, expansion of penis size

relative to body size. Possibly the minimal plesiomorphic bacular development is missed

or bypassed in the epigenetic events leading to this larger penis, accompanied either by

no selection to maintain it or even by selection against the expenditure of cellular energy.













Arcturoidea




I


Felidae other
aileroi




II =


- m


robust baculum,
complex erectile
tissue in canids


CARNIVORANS


catarrbine monkeys


-U


Hyaenidae


increased relative
s size,
baun absent





small baculum,
simple erectile tissue


nonhuman human!
apes







Li


increased relative
penis size,
aculum absent


small baculum,
simple erectile tissue


robust baculum,
complex erectile
tissue in Macaw



CATARRHINE
PRIMATES


Fig. 12. Patterns of bacular loss in carnivorans and catarrhine primates, with loss indicated
by closed circle.









The reason the phylogenetic perspective is valuable in this case is that a cross-

taxonomic correlative study would not be comparing each instance of bacular loss against

its accompanying sister group. The role of expanded penis size, for example, could not

be detected in terms of relative penis length if each species in all four orders were

included as an independent data point. The shift is confined to specific instances; there is

no gradual, consistent trend across taxa that all the data points would support.

As a side note, this and other observations by myself and D. Kelly (pers. comm.)

contradict the traditional classification of penile erection mechanisms as bony (bacular),

vascular, or integumentary. She and I suggest rather that the baculum is a subset of

vascular mechanisms and is associated with more complex vasodilatory erectile

processes, rather than as an alternative to them.



Bacular loss in the Microchiroptera

Bacula are primitive for bats (Smith and Madkour 1980) and are found in all

Megachiroptera. In the microbats (Fig. 13), the bone is present in three of four

superfamilies, being absent in Phyllostomoidea and variably present in vespertilionoids:

absent in the Miniopterinae, two molossid genera (Molossops, Promops) in Molossidae,

and in several species of otherwise bacular genera in Molossidae (Ryan 1991 a, 1991b;

see Edwards 1992 for review). No other mammalian group displays as many instances of

bacular loss as this, family of bats, and although knowledge is limited to a few specimens

of each species and some genera remain unstudied, it offers a picture both like and unlike

the instances described above.












Emballonuroidea




Rhinolophoidea





Phylostomoidea


5 other families


Miniopte ri



5 other
subfamilies

Molossidae


I Vespertilionidae


Fig. 13. Instances of bacular loss (closed circles) in microchiropteran
bats. Double circle in Molossidae indicates more than one possible
instance within the family.









At present penile anatomy of miniopterines is unknown and must be excluded

from consideration. The vespertilionids are by no means a definitive outgroup for

Molossidae, but when considered against them (following Ryan 199 1a), molossid penes

are recognizably simplified, characterized by an elongate rather than globular glans penis,

reduced accessory corpora cavernosa, and a non-vascularized prepuce (Ryan 1991b), as

well as a baculum relatively small and internalized compared with vespertilionids

presented by Hill and Harrison (1987). In this, they correspond to the pattern (Fig. 14),

but there is no evidence that the instances of bacular loss are accompanied by any change

in glans penis size. What then can account for it?

Ryan (pers. comm.) suggested that at this body size range, smaller by at least two

orders of magnitude than the other mammals who have lost their bacula, the

biomechanical role of a bone at the tip of the corpora cavernosa is met equally well by

the connective and vascular tissue itself. By this argument, there is really no difference

to these bats whether a baculum is present (sensu Koehl 1996, in that function is scale-

dependent). Although this may be true, it also might lead one to expect bacula to be

variably present within vespertilionid species rather than solely among them, and bacular

presence and absence are, as far as current evidence suggests, consistent within species.

Further Studies

The following chapters present further phylogenetic comparative analyses,

focusing on the Megachiroptera, including hypothetico-deductive tests regarding genital

evolutionary processes. Chapter Six concerns qualitative features of soft and bony

anatomy, and Chapter Seven concerns continuous measurements of bacular features.











Vespertilionidae


Mormopterus


Molossops


Cheiromeles


"elongate glans penis,
reduced a.c.c.,
nonvascular prepuce


globular glans penis,
vascularized prepuce,
relatively robust baculum

a.c.c. variable in size,
baculum present

a.c.c. small,
baculum absent

a.c.c. small,
baculumn present


Myoptems ?


Tadarida baculum present


Chaeron ?


Mops ?


Otomops ?


Nyctinomops ?

Eumops baculum absent in 2 spp.,
present in 2 spp.

Promops baculum absent


Molossus baculum present


Fig. 14. Available information on bacular and penile features in molossid bats (from Ryan 1991a,
1991b), with Vespertilionidae added as an outgroup. Ancestral condition of molossids is inferred
from commonality among known species. Bacular presence is symplesiomorphic; genera as yet
unstudied for bacular or penile features are indicated by ?.















CHAPTER 6


EVOLUTION OF MALE AND FEMALE GENITAL MORPHOLOGY IN THE
NOMINAL SUBFAMILY MACROGLOSSINAE (CHIROPTERA,
PTEROPODIDAE)

A golden rule is never to use more complex movements than are necessary to
achieve the desired results.... To hit a worthy opponent with a complex
movement is satisfying and shows one's mastery of technique; to hit the same
opponent by a simple movement is a sign of greatness. (Lee, 1975)


This chapter presents the first of two hypothesis-testing studies using the

phylogenetic method. The variables considered here are qualitative, those in the next

chapter are quantitative.

Most hypotheses concerning selection on male genital form invoke a specific

interaction with female anatomy and responsiveness, but opportunities to test these ideas

in mammals are rare. The multitude of variables and the difficulties of accumulating data

from more than a few species have limited most work to inquiries into mechanism (e.g.

Fooden 1967). The first phylogenetically-based study (Langtimm and Dewsbury 1991)

has yet to be widely emulated, but it provides a good model for focused and precise tests.

As shown in Chapter Five, the method is to map the features of interest onto a

phylogeny determined by other features (Brooks and McClennan 1991), to see if one

feature is associated with the other across taxonomic change, tracking it over evolutionary

time.









In the present chapter, the characters used for the phylogeny are taken from the

uterus and cervix of the macroglossine megabats, and those under investigation are taken

from the penis and baculum. The question is whether male genital form is selected upon

by mechanical interaction with female anatomy, as in the lock-and-key (sensu lato) or

female-resistance concepts (see Chapter Two). Cervix shape may select for glans penis

shape (cospeciation), or the two may be evolving in synchrony (coadaptation).

Alternatively, glans penis shape may select for cervix shape (cospeciation), or there may

be no evolutionary association between the two sets of anatomy, in which case the two

hypotheses under consideration may be considered falsified.



Background

The African megachiropteran species Megaloglossus woermanni has traditionally

been placed with the Asian bats of the macroglossine subgroup (Andersen 1912, Hill and

Smith 1984). These six genera are the only megachiropteran nectarivores, having the

elongated rostrum and tongue associated with this diet; these morphologies, in Andersen's

(1912) arrangement, are taken to indicate common ancestry. However, chromosomal and

immunological features suggest that M woermanni evolved nectar-feeding independently

of the Asian macroglossines and that including it with them renders the group

paraphyletic (Haiduk 1983, Haiduk et al. 1983). Uterine and cervical features identified

by Hood (1989) generate a phylogeny that, although not fully resolved, corresponds to

this arrangement without contradiction. Although it is only one of three current

competing hypotheses (see Chapter Seven) regarding megabat relationships, for purposes









of this chapter it is utilized as the base phylogeny because the uterine evolution it

includes is unambiguous (consistency index = 1.0; see Chapter Four).

According to Hood (1989), the female Asian macroglossines share derived features

-- cornual fusion and enlarged common uterine body -- that M woermanni lacks. They

do not demonstrate the most fully derived, least cornuate uterus, which is found in the

genus Nyctimene and to a lesser extent in the clade (not included in the study) containing

Balionycteris, Cynopteris, and Megaerops. Also, the Asian macroglossines are united by

synapomorphies of uterine fusion and expansion, not cervical morphology (Table 4).

The male genitalia of all genera considered by Hood (1989) and relevant to the

putative monophyly of the Macroglossinae are now available (Table 4), with species

missing from the literature having been prepared by myself, including M woermanni

collected by J.C. Kerbis Peterhans. Male characters may be mapped onto the phylogeny,

or more accurately, onto the character evolution chart suggested by Hood (1989) to test

hypotheses concerning the evolutionary association of male and female anatomy.

The general question is, how are male and female copulatory anatomy

evolutionarily associated? Specifically, is female anatomy exerting directional selection

upon the male, or vice versa? Or are both sexes' anatomies subject to a third selective

agent? Falsification of any of these hypotheses does not indicate the absence of all

selection, but it argues strongly against consistent selection on biomechanical interaction

common to all groups.








Table 4. Characters and traits utilized in cladistic analysis. Uterine traits and codings follow Hood (1989);
penile and bacular traits are coded with 0 when absent, with integer number when present


Genus


Macroglossus
Eonycteris
Syconycteris
Notopteris
Melonycteris
Nyctimene
Pteropus
Dobsonia
Megaloglossus


Genus


Macroglossus
Eonycteris
Syconycteris
Notopteris
Melonycteris
Nyctimene
Pteropus
Dobsonia
Megaloglossus


Uterine fusion


ext. fused
ext. fused
ext. fused
ext. fused
ext. fused
ext. fused
fused 1
fused 1
unfused 0


Distal flare


present
present
absent
absent
absent
absent
absent
absent
absent


Uterine body

massive 2'
median groove 2
massive 2'
massive 2'
massive 2'
smooth 0
smooth 0
smooth 0
smooth 0


Distal nub


absent
absent
absent
absent
absent
absent
var. present
absent
var. present


Portio vaginalis Cervi


low rounded 0
low rounded 0
low rounded 0
low rounded 0
low rounded 0
enlarged 3'
low rounded 0
low rounded 0
low rounded 0


present
present
absent
present
present
absent
present
present
present


Penile
spines

absent
absent
absent
absent
absent
present
absent
absent
present


within uterus 0
within uterus 0
within uterus 0
within uterus 0
within uterus 0
canals 4
within uterus 0
within uterus 0
within uterus 0


Di"1a
shaft
absent
absent
absent
absent
present
absent
absent
absent
absent


Penile crater


dorsad
distal
absent
distal
absent
ventrad
ventrad
ventrad
ventrad


Arrowhead

absent
absent
absent
absent
absent
present
absent
absent
absent


Distal elemen


absent
absent
absent
absent
present
absent
absent
absent
absent


Proximal
bifurcation


absent
absent
absent
present
absent
absent
present
present
absent


Proximal flare









The variables investigated have not been included in the phylogenetic matrix that

produced the tree, and so they are necessarily deprived of any phylogenetic information.

This may cause a problem if the phylogeny is thereby rendered incomplete. DeQueiroz

(1996) presents circumstances where this may be a problem, especially those in which

the characters of interest are expected to be of phylogenetic importance. In the present

case, removing the penis variables from the phylogenetic analysis does not decrease the

tree's stability.

This being the case, it may well be asked why uterine features are expected to be

phylogenetically meaningful, or even parsimonious in their evolution. Why should the

uterus and cervix be trustworthy, if the penis is not? Haiduk's (1983) macroglossine

phylogeny based on karyology and serology matches well with Hood's (1989) tree,

suggesting that modifications of the uterus are consistent with a valid hypothesis of

megabat diversification. Current phylogenetic trees for megabats are discussed in more

detail in the next chapter, but it is worth noting that none of those available violate the

relative positions of the nominal macroglossine genera among themselves as identified by

Hood (1989).



Methods

Specimens

During a 1992 small mammal survey in Epulu, Zaire, 10 Megaloglossus

woermanni were collected by Julian C.Kerbis Peterhans at the Ituri River

(1025'N/28035'E, at an elevation of 750 m, closed canopy lowland rainforest) and









preserved in the collections of the Field Museum of Natural History. No females were

captured. I was invited to examine these animals and allied bats by Dr. Bruce Patterson.

Specimens of all other species examined were obtained either as alcoholic-

preserved whole-body specimens or study skins from the Field Museum of Natural

History and the American Museum of Natural History. Genitalia dissected from skins

were reconstituted in 2% potassium hydroxide (KOH) for approximately 12 hours, after

which time several drops of saturate Alizarin Red solution were added. After

approximately two hours they were placed into 2% KOH again until the tissues began to

clear. They were transferred to 50% glycerin for 24 hours and then to 100% glycerin.



Analysis

Ten penile and bacular features were assigned character states and added to the

four uterine and cervical features utilized by Hood (1989) (Table 4). Character states

were assigned to nine genera based on specimens examined, using Hood (1989) for female

anatomy, and descriptions by Krutzsch (1959, 1962) to confirm observations of bacula.

The genera were arranged in the phylogeny according to Hood (1989) using MacClade

3.0 (Maddison and Maddison 1992) and features of male morphology were traced, scored

for homoplasy, and compared with the models of Brooks and McClennan (1991) for

coadaptation.

The concentrated changes character correlation test (Maddison 1990) determines

whether a character's gains and losses are associated with the origin of another character

on the phylogeny, with the null model corresponding to random origins relative to the









second feature. The test requires a fully resolved tree; the topography and resolutions of

Haiduk's (1983) tree were added to resolve Hood's (1989). The only appropriate male

features for this test are proximal and distal flares of the baculum and penile crater, tested

against positions of origin for uterine expansion and uterine fusion.



Results

Morphology

Megaloglossus woennanni (internal, external; Figs. 15, 16). JCK 23 55-2360 &

JCK 2364, JCK 2377, JCK 2395-2396. The caput penis is thickly spined and divided

sagitally on the distal end by the urethral opening. The baculum of specimen JCK 2394 is

approximately 2 mm long, located just beneath the dorsal skin; it has proximal flanges that

curve laterally, ventrally, and slightly anteriorly, as well as a distal nub. Another

specimen's (JCK 2359) baculum, not shown, is flat and ovally shaped and may represent

either intraspecific variation or a separate developmental stage.

Nyctimene rabori (external; Fig. 17). FMNH 143120. The caput penis is sparsely

and evenly spined and distally cratered on the ventral side. The baculum is located

beneath the dorsal skin and has a distinctive arrowhead shape, corresponding to that of

Nyctimene spelaea pictured by Krutzsch (1959, 1962).

Macroglossus minimus (internal; Fig. 18). FMNH 120600, 12085. The caput

penis is not spined and has a distal crater, canted slightly toward the dorsal aspect. The

baculum has proximal, lateral flanges and its distal half is also flared laterally, as presented

in outline by Krutzsch (1959). All four flanges curve ventrally as well.







































-" .lmm




DORSAL LATERAL


Fig. 15. Internal penis anatomy ofMegaloglossus woermanni (JCK 2394).




































DORSAL VENTRAL


Fig. 16. External penis anatomy of Megaloglossus woermanni (JCK 2359).











































DORSAL


LATERAL


Fig. 17. External penis anatomy of Nyctimene rabori (FMNH 143120).









































DORSAL 1 mm LATERAL


Fig. 18. Internal penis anatomy of Macroglossus minimus (FMNH 120600).









Eonycteris spelaea (external; Fig 19). FMNH 142362, 143126. The caput penis

is not spined; it is tubular in shape and has a fully distal crater. The baculum has the

same flanged shape as that ofM minimus, except that the distal half is less wide than the

proximal half, as presented in outline by Krutzsch (1959).

Notopterus macdonaldi (internal; Fig. 20) FMNH 31177, 31181, 31572, 31576.

The caput penis is not spined and has a fully distal crater. The baculum is just beneath

the dorsal skin and resembles a horseshoe with either flange curving laterally as well as

proximally.

Melonycteris melanops (internal; Fig. 21) AMNH 99871, 237311. The caput

penis is not spined and has a distinct distal element much narrow than the rest of the

penis. The baculum is located dorsally just proximal to this element; it has very wide

proximal flanges, radically curved ventrally, and a distal shaft.

Syconycteris australis (external, internal; Figs. 22, 23) AMNH 197852, 104024,

153376. The caput penis is not spined and it is completely sagitally divided by a groove,

within which is the urethral opening. On the most dorsal and anterior point, on either

side of the groove, are two distinct proximal-distal ridges. The baculum is shaft-shaped,

corresponding to that illustrated in outline by Krutzsch (1959). It is located in the dorsal

half of the interior caput penis, with wide proximally-directed flanges and a divided,

ridged distal tip. The ridges on the baculum correspond to those on the penile tip.














































1mm

DORSAL LATERAL


Fig. 19. External penis anatomy of Eonycteris spelaea (FMNH 143126).












































LATERAL 1 mm DORSAL


Fig. 20. Internal penis anatomy of Notopteris macdonaldi (FMNH 31181).