Patricia L R Brennan

• Mount Holyoke College

Alpacas (Vicugna pacos) are reported to be the rare mammal in which the penis enters the uterus in mating. To date, however, only circumstantial evidence supports this assertion. Using female alpacas culled for meat, we determined that the alpaca penis penetrates to the very tips of the uterine horns, abrading the tract and breaking fine blood vess...

Female genitalia are conspicuously overlooked in comparison to their male counterparts, limiting our understanding of sexual reproduction across vertebrate lineages. This study is the first complete description of the clitoris (hemiclitores) in female snakes. We describe morphological variation in size and shape ( n = 9 species, 4 families) that is...

Despite their evolutionary and biomedical importance, studies of the morphology and function of female genitalia have continued to lag behind those of male genitalia. While studying female genitalia can be difficult because of their soft, deformable and internal nature, recent advances in imaging, geometric analyses of shape and mechanical testing...

Synopsis The lower reproductive tract of female mammals has several competing functions including mating, tract health maintenance, and parturition. Diverse vaginal anatomy suggests interactions between natural and sexual selection, yet despite its importance, female copulatory morphology remains under-studied. We undertook a comparative study acro...

Quantification of genital variation in males and females can inform our understanding of likely copulatory interactions and evolution of genital diversity. However, no studies have quantified genital shape variation within a single snake species or examined the shape and size of both the vaginal pouch and hemipenes. Here, we examine the shape and s...

In species that copulate during non-conceptive periods, such as humans and bonobos, sexual intercourse is known to be pleasurable for females. Dolphins also copulate throughout the year, largely to establish and maintain social bonds¹ • Mann J. Establishing trust: Socio-sexual behaviour and the development of male–male bonds among Indian Ocean bot...

Quantification of genital variation in males and females can inform our understanding of likely copulatory interactions and evolution of genital diversity. However, no studies have quantified genital shape variation within a single snake species or examined the shape and size of both the vaginal pouch and hemipenes. Here, we examine the shape and s...

Synopsis Copulatory behavior and genital morphology interact to deliver sperm more effectively during mating, but the nature of this interaction has not been explored in depth in most vertebrates. Alpacas have unusually long copulations lasting 15–20 min, and a unique copulatory behavior, where the penis intromits all the way past the cervix, into...

The field of post-copulatory sexual selection investigates how female and male adaptations have evolved to influence the fertilization of eggs while optimizing fitness during and after copulation, when females mate with multiple males. When females are polyandrous (one female mates with multiple males), they may optimize their mating rate and contr...

Comparisons of 3D shapes have recently been applied to diverse anatomical structures using landmarking techniques. However, discerning evolutionary patterns can be challenging for structures lacking homologous landmarks. We used alpha shape analyses to quantify vaginal shape complexity in 40 marine mammal specimens including cetaceans, pinnipeds, a...

The phallic glans of the American alligator (Alligator mississippiensis) is the distal termination of the semen-conducting sulcus spermaticus and during copulation has the closest, most intimate mechanical interactions with the female urodeum, the middle cloacal chamber that contains the opening to the vaginal passages and oviducts. However, the de...

Interview with Patricia Brennan, who studies genital co-evolution and sexual conflict in vertebrates at Mount Holyoke College.

In internal fertilizers, copulatory behavior and genital morphology are intricately connected because there are many functional and morphological challenges that genitalia must overcome for successful transfer of male gametes into the female reproductive tract. In addition, selective forces can act either on copulatory behavior and genitalia indepe...

Asymmetric genitalia and lateralized mating behaviors occur in several taxa, yet whether asymmetric morphology in one sex correlates or coevolves with lateralized mating behavior in the other sex remains largely unexplored. While lateralized mating behaviors are taxonomically widespread, among mammals they are only known in the harbor porpoise (Pho...

Whales, dolphins, and porpoises have unusual vaginal folds of unknown function(s) that are hypothesized to play an important role in sexual selection. The potential function of vaginal folds was assessed by testing the mechanical properties of common bottlenose dolphin (Tursiops truncatus) reproductive tract tissues in 6 different regions and acros...

Genital structures are among the most variable in nature and have been suggested to evolve at exceptionally high rates. However, the vast majority of research on genital morphology has been done on male genitalia. We present one of the few studies of female genital shape using geometric morphometrics, and the first of such studies to employ 3D geom...

Animal pigmentation is incredibly diverse, serving a variety of functions. However, the function of the pigmentation that surrounds the testes of some vertebrates is unknown. Why are the tissues surrounding the testes (scrotum, tunica vaginalis and/or tunica albuginea) melanized in some species but not others? We examined this question in bats, whe...

Male genital diversification is likely the result of sexual selection. Female genital diversification may also result from sexual selection, although it is less well studied and understood. Female genitalia are complex among whales, dolphins, and porpoises, especially compared to other vertebrates. The evolutionary factors affecting the diversity o...

Genitalia are morphologically variable across many taxa and in physical contact during intromission, but little is known about how variation in form correlates with function during copulation. Marine mammals offer important insights into the evolutionary forces that act on genital morphology because they have diverse genitalia and are adapted to aq...

Ducks are an excellent group to study avian genital evolution. Penis morphology of ducks is diverse, and penis length and elaboration are positively correlated with levels of male competition resulting from forced extra-pair copulations, and with female genital elaboration resulting from sexual conflict. Here we examined whether penis morphology is...

Economic and public support of science relies on an explicit understanding of why basic science is relevant and important to people’s daily lives. Though basic science is essential to solving problems, its importance is often not understood by the general public. In the case of evolutionary biology, this lack of understanding is surprising, given t...

Mammalian penises are morphologically diverse, including a highly variable and taxonomically informative baculum (os penis), and variable penile spines, both of which are possessed by many—but not all—species. To understand the evolution of genital morphologies, as well as the potential role of both the baculum, and penile spines that directly inte...

Male intromittent organs are exceedingly diverse, yet we know comparatively little about female genital diversity. However, the most direct mechanical interaction between males and females occurs during copulation, and therefore, genital coevolution is expected to be widespread. This means that diversification of male structures must influence dive...

Table S1. Behavioral data.

Table S2. Eggshell reflectance.

Appendix S1. Extended materials and methods.

Evolutionary hypotheses regarding the function of eggshell phenotypes, from solar protection through mimicry, have implicitly assumed that eggshell appearance remains static throughout the laying and incubation periods. However, recent research demonstrates that egg coloration changes over relatively short, biologically relevant timescales. Here, w...

Natural selection and postcopulatory sexual selection, including sexual conflict, contribute to genital diversification. Fundamental first steps in understanding how these processes shape the evolution of specific genital traits are to determine their function experimentally and to understand the interactions between female and male genitalia durin...

Amniote penises come in many shapes but are missing from the basal tuatara. This has been taken as evidence for multiple evolutionary origins of the penis. Now, genital swellings have been found in tuatara embryos, arguing for a single origin.

Pigment-based coloration is a common trait found in a variety of organisms across the tree of life. For example, calcareous avian eggs are natural structures that vary greatly in color, yet just a handful of tetrapyrrole pigment compounds are responsible for generating this myriad of colors. To fully understand the diversity and constraints shaping...

UHPLC/MS chromatograms for pigment extracts from all avian eggshells and molluscan shells included in the study. (PDF)

Avian eggshell and molluscan shell purchase or collection locations. (PDF)

Genital coevolution between the sexes is expected to be common because of the direct interaction between male and female genitalia during copulation. Here we review the diverse mechanisms of genital coevolution that include natural selection, female mate choice, male-male competition, and how their interactions generate sexual conflict that can lea...

For internally-fertilizing animals, sperm storage is a nearly ubiquitous trait that has enormous evolutionary implications. Female sperm storage (FSS) may influence the degree of pre- and post-copulatory sexual selection as well as the ability of females to time reproduction with periods of resource availability, thereby ensuring an ample supply of...

Sperm storage, the extended maintenance of viable sperm, probably occurs in most internally fertilizing animals. Because it temporally separates mating from conception, sperm storage can be adaptive in ecologically diverse habitats and affect life histories, mating systems, cryptic female choice, sperm competition, and sexual conflict. Sperm storag...

The role of pigments in generating the colour and maculation of birds' eggs is well characterized, whereas the effects of the eggshell's nanostructure on the visual appearance of eggs are little studied. Here, we examined the nanostructural basis of glossiness of tinamou eggs. Tinamou eggs are well known for their glossy appearance, but the underly...

Reproductive specializations in birds have provided intriguing model systems to better understand the role of endocrine mechanisms that regulate phenotype expression and the action of sexual selection. A comparative approach can elucidate how endocrine systems associated with control of sexual differentiation, sexual maturation, and reproductive ph...

•Politically motivated attacks on animal behaviour projects are common.•We offer strategies to help with responding to unjustified attacks.•We provide a list of animal behaviour research that has applied benefits to society.•Increased education and outreach efforts are crucial to increase support for our science.

Avian genitalia, particularly in waterfowl, are extremely diverse. Penis morphology varies among species, and penis length and elaboration are associated with the frequency of forced extra-pair copulations, yet the developmental mechanisms responsible for this variation are unknown. In addition, females have a small phallic structure that is homolo...

C oncerns about the US budget deficit are pushing government research funding toward utilitar-ian and translational research at the expense of basic science (Hand etal. 2013). Science funding decisions are increasingly at risk of becom-ing politicized, and reductions in basic science funding are often justi-fied as eliminating wasteful govern-ment...

Sexual conflict over mating can result in sex-specific morphologies and behaviours that allow each sex to exert control over the outcome of reproduction. Genital traits, in particular, are often directly involved in conflict interactions. Via genital manipulation, we experimentally investigated whether genital traits in red-sided garter snakes infl...

The morphological differences in female genitalia within and between species are little studied and poorly understood, yet understanding patterns of variation in female genitalia can provide insights into mechanisms of genital evolution. The present study aimed to explore the patterns of intraspecific and interspecific variation in female genitalia...

Losing the penis in species with internal fertilization may seem paradoxical, but birds have managed to do it multiple times. A new study addresses one developmental mechanism responsible for penis reduction in birds, and opens the door to further examination of this little understood evolutionary phenomenon.

Predators can adversely impact nesting success and therefore the presence of seemingly conspicuous eggshells would appear maladaptive. The ratites, especially the tinamous, exhibit a diverse array of eggshell colours that appear to differ strikingly from their nesting substrate, while most ground-nesting species that do not build a nest lay camoufl...

How does genetic innovation translate into ecological innovation? Although evo-devo has successfully linked genes to morphology, the next stage is elucidating how genes predict resource use. This can be attained by broadening the focus of evo-devo from [genes→morphology], to [genes→morphology→functional ecology]. We suggest that the fields of evo-d...

Mixed paternity or the presence of offspring sired by more than one male in a brood is common in birds. The hypothesis that mixed paternity should be low when male involvement in care is high has received widespread support in among-species comparisons that report a negative relationship between the percentage of mixed paternity and the extent of m...

Sexual conflict occurs when the evolutionary interests of the sexes differ and it broadly applies to decisions over mating, fertilization and parental investment. Recently, a narrower view of sexual conflict has emerged in which direct selection on females to avoid male-imposed costs during mating is considered the distinguishing feature of conflic...

Ultraviolet (UV) light-transmitted signals play a major role in avian foraging and communication, subserving functional roles in feeding, mate choice, egg recognition, and nestling discrimination. Sequencing functionally relevant regions of the short wavelength sensitive type 1 (SWS1) opsin gene that is responsible for modulating the extent of SWS1...

The erection mechanism of the penis in most vertebrates is blood vascular. A major evolutionary transition occurred in birds, where the erection mechanism changed from blood vascular to lymphatic. Within birds, however, the erection mechanism of the ratite penis has remained unknown. Early work suggested that the erection mechanism in ostrich Strut...

The erection mechanism of the penis in most vertebrates is blood vascular. A major evolutionary transition occurred in birds, where the erection mechanism changed from blood vascular to lymphatic. Within birds, however, the erection mechanism of the ratite penis has remained unknown. Early work suggested that the erection mechanism in ostrich Strut...

The study of avian eggshell structure, including composition, pigmentation, thickness, and strength, has important ecological and economic implications. Previous investigators have used a variety of techniques to derive either direct measures or indirect estimates of eggshell thickness. Assessing the repeatability and method agreement of different...

Egg camouflage has been found to reduce predation in several ground-nesting species. Therefore, the evolution of eggs that lack camouflage in ground nesting birds is puzzling. Even though clutch predation in the tropics is high, tinamous are the only tropical ground-nesting birds that do not build a nest and do not lay cryptic eggs. I studied preda...

The known chemical basis of diverse avian eggshell coloration is generated by the same two classes of tetrapyrrole pigments in most living birds. We aimed to extend the evolutionary scope of these patterns by detecting pigments from extinct birds’ eggs. In our samples biliverdin was successfully extracted from subfossil shell fragments of the blue-...

Coevolution of male and female genitalia in waterfowl has been hypothesized to occur through sexual conflict. This hypothesis raises questions about the functional morphology of the waterfowl penis and the mechanics of copulation in waterfowl, which are poorly understood. We used high-speed video of phallus eversion and histology to describe for th...

I monitored Great Tinamou (Tinamus major) clutches between February and May 2000–2002 at La Selva Biological Station in Costa Rica, and describe observations on incubation behavior and nest attendance. Incubation lasted 17 days and began after the clutch was completed. Nest attendance during monitoring was high: birds were incubating during 249 nes...

In 2001 the journal Nature published an extraordinary image of a male duck. The Argentine Lake Duck Oxyura vittata, is a little-known species, but this particular photograph would make it unforgettably famous because of the bird's gargantuan penis. Suspended from a loop of monofilament line, the bemused little bird hangs somewhat unnaturally, albei...

Despite a long history of anatomical studies in birds, the genitalia of most avian species remain undescribed. Birds are the only vertebrate taxon with internal fertilization where an intromittent phallus has been lost in most species. Studying the anatomical transitions of the avian phallus in those species where it is still present, allows us to...

Eighteen microsatellite loci were isolated from great tinamous (Tinamus major), which are large terrestrial birds found in the Neotropics. These are the first primers developed for the Order Tinamiformes. Paternity analyses are possible because the levels of heterozygosity are sufficiently high (0.29-0.90).

Molecular phylogeny of waterfowl species used in the comparative analysis. Bayesian posterior probabilities (PP) are indicated in red for those nodes with less than 100% PP. (0.09 MB DOC)

Length (cm) and elaboration of waterfowl genitalia. (0.06 MB DOC)

Most birds have simple genitalia; males lack external genitalia and females have simple vaginas. However, male waterfowl have a phallus whose length (1.5->40 cm) and morphological elaborations vary among species and are positively correlated with the frequency of forced extra-pair copulations among waterfowl species. Here we report morphological co...

Resumen. – Técnicas para el estudio de la ecología del comportamiento de tinamúes de bosque (Tinamidae). – Por razones metodológicas, los tinamúes son uno de los ordenes de aves menos estudiados, a pesar de que son primitivos entre las aves actuales y muestran comportamientos poco comunes y fascinantes que son poco entendidos. Primero, todos los ti...

Most birds have simple genitalia; males lack external genitalia and females have simple vaginas. However, male waterfowl have a phallus whose length (1.5-.40 cm) and morphological elaborations vary among species and are positively correlated with the frequency of forced extra-pair copulations among waterfowl species. Here we report morphological co...