Rapid differentiation and asynchronous coevolution of male and female genitalia in stink bugs

Despite claims that genitalia are among the fastest evolving phenotypes, few studies have tested this trend in a quantitative and phylogenetic framework. In systems where male and female genitalia coevolve, there is a growing effort to explore qualitative patterns of evolution and their underlying mechanisms, but the temporal aspect remains overlooked. An intriguing question is how fast male and female genitalia may change in a coevolutionary scenario. Here, we apply a series of comparative phylogenetic analyses to reveal a scenario of correlated evolution and to investigate how fast male and female external, nonhomologous and functionally integrated genitalia change in a group of stink bugs. We report three findings: the female gonocoxite 8 and the male pygophore showed a clear pattern of correlated evolution, both genitalia were estimated to evolve much faster than nongenital traits, and rates of evolution of the male genitalia were twice as fast as the female genitalia. Our results corroborate the widely held view that male genitalia evolve fast and add to the scarce evidence for rapidly evolving female genitalia. Different rates of evolution exhibited by males and females suggest either distinct forms or strengths of selection, despite their tight functional integration and coevolution. The morphological characteristics of this coevolutionary trend are more consistent with a cooperative adjustment of the genitalia, suggesting a scenario of female choice, morphological accommodation, lock‐and‐key or some combination of the three.     

Cryptic female exaggeration: the asymmetric female internal genitalia of Kaliana yuruani (Araneae: Pholcidae)

Males of the Venezuelan pholcid spider Kaliana yuruani have unique genitalia, with the procursi about six times as long as usual in the family. The present article describes the previously unknown female, searching for a morphological correlate in the female genitalia to the male's exaggeration. Reconstruction of histological serial sections reveals an internal female complexity that is unequalled in pholcid spiders. An intricate system of ducts and folds is arranged in an asymmetric way, making this the third known case of genital asymmetry in spiders. The term "cryptic female exaggeration" is used in analogy to cryptic female choice, pointing to the fact that from the outside, the female genitalia do not appear unusual. I propose that cryptic female exaggeration may be relatively common in copulatory structures if male exaggerations need to be evaluated according to the female choice by mechanical fit model. Finally, the evolution of genital asymmetry in spiders is contrasted with that in insects.     

HAVE MALE AND FEMALE GENITALIA COEVOLVED? A PHYLOGENETIC ANALYSIS OF GENITALIC MORPHOLOGY AND SEXUAL SIZE DIMORPHISM IN WEB‐BUILDING SPIDERS (ARANEAE: ARANEOIDEA)

Sexual size dimorphism (SSD) can strongly influence the evolution of reproductive strategies and life history. If SSD is extreme, and other characters (e.g., genitalic size) also increase with size, then functional conflicts may arise between the sexes. Spiders offer an excellent opportunity to investigate this issue because of their wide range of SSD. By using modern phylogenetic methods with 16 species of orb-weaving spiders, we provide strong evidence for the "positive genitalic divergence" model, implying that sexual genitalic dimorphism (SGD) increases as SSD increases. This pattern is supported by an evolutionary mismatch between the absolute sizes of male and female genitalia across species. Indeed, our findings reveal a dramatic reversal from male genitalia that are up to 87x larger than female genitalia in size-monomorphic species to female genitalia that are up to 2.8x larger in extremely size-dimorphic species. We infer that divergence in SGD could limit SSD both in spiders, and potentially in other taxa as well. Further, male and female body size, as well as male and female genitalia size, are decoupled evolutionarily. Finally, we show a negative scaling (hypoallometry) of male and female genitalic morphology within sexes. Evolutionary forces specific to each sex, such as larger female size (increased fecundity) or smaller male size (enhanced mate-searching ability), may be balanced by stabilizing selection on relative genitalic size.     

Copulatory mechanism in a sexually cannibalistic spider with genital mutilation (Araneae: Araneidae: Argiope bruennichi)

Genitalia are among the fastest evolving morphological traits as evidenced by their common function as diagnostic traits in species identification. Even though the main function of genitalia is the successful transfer of spermatozoa, the presence of diverse structures that are obviously not necessary for this suggests that genitalia are a target of sexual selection. The male genitalia of many spider species are extremely complex and equipped with numerous sclerites, plates and spines whose functions are largely unknown. Selection on male genitalia may be particularly strong in sexually cannibalistic spiders, where mating success of males is restricted to a single female. We investigated the copulatory mechanism of the sexually cannibalistic orb weaving spider Argiope bruennichi by shock freezing mating pairs and revealed a complicated interaction between the appendices and sclerites that make up the male gonopods (paired pedipalps). The plate that covers the female genital opening (scape) is secured between two appendices of the male genital bulb, while three sclerites that bear the sperm duct are unfolded and extended into the female copulatory opening. During copulation, females attack and cannibalise the male and males mutilate their genitalia in about 80% of cases. Our study demonstrates that (i) genital coupling is largely accomplished on the external part of the female genitalia, (ii) that the mechanism requires an interaction between several non-sperm-transferring structures and (iii) that there are two predetermined breaking points in the male genitalia. Further comparative work on the genus Argiope will test if the copulatory mechanism with genital mutilation indeed is an adaptation to sexual cannibalism or if cannibalism is a female counter adaptation to male monopolisation through genital plugging.     

Hierarchical comparative analysis of genetic and genitalic geographical structure: testing patterns of male and female genital evolution in the scarab beetle Phyllophaga hirticula (Coleoptera: Scarabaeidae)

It is generally accepted that genitalia are among the fastest evolving characters in insects and that selection on these structures may increase speciation rates in groups with polygamous mating systems. If selection is causing genitalic divergence between or among populations of a species, one prediction is that geographical structure of genitalic morphology would be in place before genetic structure of a rapidly evolving neutral marker. The current study tests this hypothesis in the geographically widespread scarab beetle Phyllophaga hirticula by evaluating whether standing variation in male and female genitalia is more or less geographically structured than a mitochondrial genetic marker. Geographical structure of mitochondrial (mt)DNA and male and female genitalic shape were analysed using analysis of variance, multivariate analysis of variance, Mantel tests, and tests of spatial autocorrelation. The results show that, although female genitalia are more geographically structured than mtDNA, male genitalia are not. This pattern suggests that selection on female genitalic variation may be causing divergence of these structures among populations.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 135–149.     

The evolution of female genitalia

Female genitalia have been largely neglected in studies of genital evolution, perhaps due to the long‐standing belief that they are relatively invariable and therefore taxonomically and evolutionarily uninformative in comparison with male genitalia. Contemporary studies of genital evolution have begun to dispute this view, and to demonstrate that female genitalia can be highly diverse and covary with the genitalia of males. Here, we examine evidence for three mechanisms of genital evolution in females: species isolating ‘lock‐and‐key’ evolution, cryptic female choice and sexual conflict. Lock‐and‐key genital evolution has been thought to be relatively unimportant; however, we present cases that show how species isolation may well play a role in the evolution of female genitalia. Much support for female genital evolution via sexual conflict comes from studies of both invertebrate and vertebrate species; however, the effects of sexual conflict can be difficult to distinguish from models of cryptic female choice that focus on putative benefits of choice for females. We offer potential solutions to alleviate this issue. Finally, we offer directions for future studies in order to expand and refine our knowledge surrounding female genital evolution.     

Experimental demonstration of possible cryptic female choice on male tsetse fly genitalia

A possible explanation for one of the most general trends in animal evolution - rapid divergent evolution of animal genitalia - is that male genitalia are used as courtship devices that influence cryptic female choice. But experimental demonstrations of stimulatory effects of male genitalia on female reproductive processes have generally been lacking. Previous studies of female reproductive physiology in the tsetse fly Glossina morsitans suggested that stimulation during copulation triggers ovulation and resistance to remating. In this study we altered the form of two male genital structures that squeeze the female's abdomen rhythmically in G. morsitans centralis and induced, as predicted, cryptic female choice against the male: sperm storage decreased, while female remating increased. Further experiments in which we altered the female sensory abilities at the site contacted by these male structures during copulation, and severely altered or eliminated the stimuli the male received from this portion of his genitalia, suggested that the effects of genital alteration on sperm storage were due to changes in tactile stimuli received by the female, rather than altered male behavior. These data support the hypothesis that sexual selection by cryptic female choice has been responsible for the rapid divergent evolution of male genitalia in Glossina; limitations of this support are discussed. It appears that a complex combination of stimuli trigger female ovulation, sperm storage, and remating, and different stimuli affect different processes in G. morsitans, and that the same processes are controlled differently in G. pallidipes. This puzzling diversity in female triggering mechanisms may be due to the action of sexual selection.     

Natural selection and genital variation: a role for the environment,parasites and sperm ageing?

Male genitalia are more variable between species (and populations) than other organs, and are more morphologically complex in polygamous compared to monogamous species. Therefore, sexual selection has been put forward as the major explanation of genital variation and complexity, in particular cryptic female choice for male copulatory courtship. As cryptic female choice is based on differences between males it is somewhat paradoxical that there is such low within-species variation in male genitalia that they are a prime morphological identification character for animal species. Processes other than sexual selection may also lead to genitalia variation but they have recently become neglected. Here I focus on pleiotropy and natural selection and provide examples how they link genitalia morphology with genital environments. Pleiotropy appears to be important because most studies that specifically tested for pleiotropic effects on genital morphology found them. Natural selection likely favours certain genital morphology over others in various environments, as well as by reducing re-infection with sexually transmitted diseases or reducing the likelihood of fertilisation with aged sperm. Both pleiotropy and natural selection differ locally and between species so may contribute to local variation in genitalia and sometimes variation between monogamous and polygamous species. Furthermore, the multitude of genital environments will lead to a multitude of genital functions via natural selection and pleiotropy, and may also contribute to explaining the complexity of genitalia.     

Coevolution of male and female reproductive structures in Drosophila

The morphology of male genitalia whilst stable within species, exhibits huge interspecific variation. This variation is likely to be as a result of sexual selection due to the direct involvement of these reproductive structures in mating and sperm transfer. In contrast, internal soft tissue components of the genitalia are generally poorly investigated as they are not directly involved in physical and mechanical adequacy during sperm transfer. However, these soft tissue structures may also drive differential male–female interactions, particularly in internally fertilising organisms where females have the ability to store sperm and bias male reproductive success. In this paper we use the drosophila model to investigate the role of male and female reproductive elements in sexual selection. Our meta-analysis supplemented with additional new data clearly shows that within species, sperm length versus testis length, and sperm length versus seminal receptacle length, are highly correlated. Thus, independent of the phylogenetic relationship among species, gamete evolution is likely to result in sexual selection interactions that drive the evolution of internal reproductive components in both sexes. Our results and discussion of the literature highlight the importance of considering internal soft structures that may influence fertilisation, when investigating selective forces acting on the evolution of reproductive traits.     

The function of female resistance behavior: intromission by male coercion vs. female cooperation in sepsis flies (Diptera: Sepsidae)

Female resistance behavior that occurs prior to intromission does not by itself imply forced copulation. Such behavior may function instead as a test of the male in order to favor some males over others, or to induce the male to desist. Thus, male persistence and forcefullness may sometimes be better described as persuasion rather than coercion. Under the persuasion hypothesis, the male only gains intromission due to an active response of the female. Under the coercion hypothesis, male and female are opposed in a physical battle which the female loses if copulation occurs. In species in which males are morphologically incapable of forcing intromission without active female cooperation (I argue here that this is probably a very common situation), data on the behavioral and ecological context in which resistance occurs can distinguish between the two possibilities. Partially congruent functions of resistance, seen from the female point of view, are female resistance to screen (male persuasion), and female resistance to avoid males non-selectively (male coercion). Sepsis flies illustrate these ideas. Females often struggle energetically in apparent attempts to dislodge mounted males and to prevent intromission, and males grasp females with powerful species-specific structures on their front legs and genitalia. This suggests the possibility of coerced intromission. But behavioral and morphological evidence demonstrate that active female cooperation occurs at the moment of intromission, and that males are probably dependent on this cooperation because they are not morphologically equipped to force their genitalia into those of an uncooperative female. Despite the impression from previous publications, male insects in general may seldom be able to achieve intromission by genitalic force. The species-specific forms of the grasping genitalia of male sepsis are probably not the result of an evolutionary arms race between coercive males and unselectively resistant females.     

基于雌蚊尾器形态的中国阿蚊属分类研究

【目的】明确阿蚊Armigeres雌蚊尾器在分类鉴定中的价值。【方法】依据在云南长期采集的标本, 观察了我国阿蚊属Armigeres正式记录的16种雌蚊尾器构造, 对雌蚊尾器的形态进行了系统描述和分类研究。【结果】编制两个亚属和16种阿蚊的雌蚊尾器分类检索表。【结论】每一种雌蚊尾器与雄蚊尾器一样, 都具有种的固定的特征, 是种的重要分类依据。     

Pre- and Post-Copulatory Mate Selection Mechanisms in an African Dung Beetle, <Emphasis Type="Italic">Circellium bacchus</Emphasis> (Coleoptera: Scarabaeidae)

Females of most taxa mate selectively. Mate selection may be: (1) pre-copulatory, involving active female choice and male-male competition, and (2) post-copulatory, with cryptic female choice and sperm competition. Because female dung beetles (Circellium bacchus) invest heavily in parental care by ball-rolling and remaining with developing larva they are, therefore, expected to be highly selective when mating. Mate choice in this species was investigated via behavioral observations and investigations of genital allometry of both sexes, leading to conclusions about the mechanisms of, and male characteristics important in, female choice. Male–male competition seems to be crucial in mate selection of C. bacchus, although the females appeared to show no active mate choice. There is a negative allometric relationship between genital size and body size of males as predicted by the ‘one size fits all’ hypothesis (where males have genitalia that fit average-sized females). For the females, no relationship was found between genital size and body size. This might be as a result of the non-sclerotized nature of female genitalia, which may allow for greater morphological plasticity.     

Female genitalia,reproductive cycle and sperm storage in Armadillidium vulgare (Crustacea,Isopoda, Oniscidea)

Light and electron microscopic studies that we have published in the past have reported many aspects of the reproductive process in Armadillidium vulgare with particular emphasis on the reconstruction of female genitalia. Together this body of work provides an almost complete, albeit fragmented picture of these processes and include many data on sperm storage and sperm translocation. Females of A. vulgare have a pair of cuticular genitalia in the lumen of the oviduct. For insemination, these genitalia can receive the copulatory organs of males formed by the elongated tips of the first two pleon endopods. During transitions between reproductive (parturial) and non-reproductive (normal, non-parturial) moult cycles the genitalia undergo intriguing structural changes resulting in two types of genitalia. Throughout their reproductive lifetime, either type is reconstructed after each moult depending on the reproductive phase of the female. In this review, we integrate the events that occur during a reproductive cycle with particular emphasis on the genitalia reconstruction and sperm storage, and discuss functional aspects of the genitalia. Thereby, we provide a case model that can be useful for further studies on genitalia diversity and female reproductive strategies in terrestrial isopods.     

Sexually antagonistic coevolution in insects is associated with only limited morphological diversity

Morphological traits involved in male-female sexual interactions, such as male genitalia, often show rapid divergent evolution. This widespread evolutionary pattern could result from sustained sexually antagonistic coevolution, or from other types of selection such as female choice or selection for species isolation. I reviewed the extensive but under-utilized taxonomic literature on a selected subset of insects, in which male-female conflict has apparently resulted in antagonistic coevolution in males and females. I checked the sexual morphology of groups comprising 500-1000 species in six orders for three evolutionary trends predicted by the sexually antagonistic coevolution hypothesis: males with species-specific differences and elaborate morphology in structures that grasp or perforate females in sexual contexts; corresponding female structures with apparently coevolved species-specific morphology; and potentially defensive designs of female morphology. The expectation was that the predictions were especially likely to be fulfilled in these groups. A largely qualitative overview revealed several surprising patterns: sexually antagonistic coevolution is associated with frequent, relatively weak species-specific differences in males, but male designs are usually relatively simple and conservative (in contrast to the diverse and elaborate designs common in male structures specialized to contact and hold females in other species, and also in weapons such as horns and pincers used in intra-specific battles); coevolutionary divergence of females is not common; and defensive female divergence is very uncommon. No cases were found of female defensive devices that can be facultatively deployed. Coevolutionary morphological races may have occurred between males and females of some bugs with traumatic insemination, but apparently as a result of female attempts to control fertilization, rather than to reduce the physical damage and infections resulting from insertion of the male's hypodermic genitalia. In sum, the sexually antagonistic coevolution that probably occurs in these groups has generally not resulted in rapid, sustained evolutionary divergence in male and female external sexual morphology. Several limitations of this study, and directions for further analyses are discussed.     

Female genitalia are moderately informative for phylogenetic inference and not concerted with male genitalia in Saprininae beetles (Coleoptera: Histeridae)

Our study – the first of its kind within Histeridae (Coleoptera) – deals with the female genitalia in the subfamily Saprininae, with respect to their variation and utility for phylogenetic reconstruction. Morphology of female genitalia (chiefly characters of the spermatheca, and variation of the gonocoxites, articulating sclerites and gonostyli) is herein described and depicted. We perform parsimony‐based morphological phylogenetic analyses of Saprininae using combined datasets that comprise somatic, male and female genitalia characters. We assess phylogenetic utility of female genital characters and test for their correlation with male genital characters. We found that female genitalia are generally moderately informative for phylogenetic reconstruction. The somatic and male genitalia characters (on average) possess higher phylogenetic signal; female genitalia provide better support and diagnoses for particular clades (emphasizing their importance for systematics), in which the evolution of female genitalia can be linked to environmental factors imposed by the mode of life. Regardless of the degree of informativeness, structures of female genitalia represent an additional interesting and important source of information for systematics and taxonomy. We did not find any evidence of correlated evolution between male and female genitalia.     

Fine needle aspiration cytology of mammary duct ectasia: report of a case with novel cytologic and immunocytochemical findings.

BACKGROUND: Mammary duct ectasia (MDE), or periductal mastitis, is a well-defined clinical entity with a characteristic histopathologic appearance on breast biopsy specimens. However, the cytologic features of MDE have been described only recently in the cytopathology literature, and fine needle aspiration (FNA) cytologic findings are based mainly on a small number of case reports in the English-language literature. Therefore, awareness of this entity and recognition of its cytomorphologic features could aid in a more accurate diagnosis. We report the novel cytologic and immunocytochemical findings on a case of MDE that was confirmed by histologic examination on a subsequent biopsy. CASE: We report the findings of breast FNA cytology in a 50-year-old female with a mammographically and clinically suspicious lesion. Cytology displayed a paucicellular aspirate, typified by a few scattered, cohesive clusters of ductal epithelial cells with mild nuclear atypia and distinct, peripherally located myoepithelial cells. Intermingled within the ductal elements were numerous polygonal cells with abundant, finely vacuolated cytoplasm that were immunoreactive for macrophage-specific antibody, CD68. The background consisted of a variable number of foam cells and negligible amount of blood. CONCLUSION: The current case of MDE demonstrates cytomorphologic features that may pose diagnostic problems, particularly as a consequence of variable cytologic atypia this entity may present on FNA cytology. This diagnostic difficulty is compounded because of the abnormal mammographic and suspicious clinical findings that may be associated with MDE. CD68 immunoreactivity is a useful ancillary tool to verify the histiocytic, rather than epithelial and potentially neoplastic, nature of multivacuolated cells. To the best of our knowledge, there has been no prior reported case of MDE in the English-language literature studied utilizing CD68 antibody. This case report emphasizes that MDE is a heterogeneous entity with diverse cytomorphologic features. FNA cytology in conjunction with immunocytochemistry might permit accurate classification in the proper clinical setting.     

SEXUAL SELECTION IS INVOLVED IN SPECIATION IN A LAND SNAIL RADIATION ON CRETE

We investigated the importance of sexual selection in facilitating speciation in a land snail radiation on Crete. We used differences in the genitalia of the Cretan Xerocrassa species as potential indices of sexual selection. First, we rejected the hypothesis that differences in the genitalia of the Xerocrassa species can be explained by genetic drift using coalescent simulations based on a mitochondrial gene tree. Second, we showed that there is no evidence for the hypothesis that the differences in the genitalia can be explained by natural selection against hybrids under the assumption that this is more likely in geographically overlapping species pairs and clades. Third, we showed that there is a positive scaling between male spermatophore-producing organs and female spermatophore-receiving organs indicating sexual coevolution. The spermatophore enables the sperm to escape from the female gametolytic organ. Thus, the coevolution might be a consequence of sexual conflict or cryptic female choice. Finally, we showed that the evolution of differences in the length of the flagellum that forms the tail of the spermatophore is concentrated toward the tips of the tree indicating that it is involved in speciation. If speciation is facilitated by sexual selection, niches may remain conserved and nonadaptive radiation may result.     

Static allometry and animal genitalia

A survey of 117 species of arthropods and 17 species of vertebrates showed a strong trend for male genitalia to have relatively low static allometric values. This trend contrasts with the allometry of other structures under sexual selection, which usually show steep allometric slopes. The trend to low allometric genital values is less consistent in mammals than in arthropods. Data not in accord with the previous the "one-size-fits-all" explanation for low allometric slopes in genitalia, which was based on sexual selection by female choice, suggest a more general version that includes both natural selection and sexual selection, and involves both mechanical fit and stimulation. Less-complete data on the female genitalia of arthropods suggest a trend to similar low allometric slopes, and may also be explained by mechanical fit and stimulatory one-size-fits-all arguments.     

Copulation behaviour of Glossina pallidipes (Diptera: Muscidae) outside and inside the female, with a discussion of genitalic evolution

If species-specific male genitalia are courtship devices under sexual selection by cryptic female choice, then species-specific aspects of the morphology and behaviour of male genitalia should often function to stimulate the female during copulation. The morphology and behaviour of the complex, species-specific male genitalia of the tsetse fly, Glossina pallidipes Austen, were determined from both direct observations and dissections of flash-frozen copulating pairs; we found that some male genitalic traits probably function to stimulate the female, while others function to restrain her. The male clamps the ventral surface of the female's abdomen tightly with his powerful cerci. Clamping does not always result in intromission. Clamping bends the female's body wall and her internal reproductive tract sharply, posteriorly and dorsally, and pinches them tightly. The male performed sustained, complex, stereotyped, rhythmic squeezing movements with his cerci that were not necessary to mechanically restrain the female and appeared instead to have a stimulatory function. Six different groups of modified setae on and near the male's genitalia rub directly against particular sites on the female during squeezing. The designs of these setae correlate with the force with which they press on the female and the probable sensitivity of the female surfaces that they contact. As expected under the hypothesis that these structures are under sexual selection by female choice, several traits suspected to have stimulatory functions have diverged in G. pallidipes and its close relative, G. longipalpis. Additional male non-genitalic behaviour during copulation, redescribed more precisely than in previous publications, is also likely to have a courtship function. The elaborate copulatory courtship behaviour and male genitalia may provide the stimuli that previous studies showed to induce female ovulation and resistance to remating.