Variation In Genital Morphology Research Articles

A new species of Liphistius from Myanmar and description of the actual male of L. birmanicus Thorell, 1897 (Araneae, Mesothelae, Liphistiidae).

Five Liphistius Schiödte, 1849 species of the primitively segmented spider family Liphistiidae are currently known from Myanmar. Here, we described a new species, Liphistiuspyinoolwinsp. nov. (♂♀), which was collected from Pyin Oo Lwin, Mandalay Region, Myanmar, diagnosed based on its genital morphology. The specimens (2♂♂, 5♀♀) collected by Walter C. Sedgwick from Pyin Oo Lwin in 1982 were misidentified as L.birmanicus Thorell, 1897 and are treated here as the newly described species. Accordingly, we described the males of L.birmanicus for the first time, redescribed its female, using newly collected specimens from Yadò, Than Taung and Kalekho Atet townships, Kayin State. We also provided information on the variation in genital morphology of both species, and their relationships within the birmanicus-group of species.

Knockdown of rotund gene through larval RNA interference affects genital and elytral morphology in the ground beetle Carabus maiyasanus (Coleoptera: Carabidae)

AbstractInterspecific variation in genital morphology contributes to prezygotic reproductive isolation in many insect species. However, developmental genes affecting genital morphology are poorly understood. We undertook larval RNA interference (RNAi) experiments with rotund (rn) gene in the ground beetle Carabus (Ohomopterus) maiyasanus to examine the knockdown effects of this gene on genital development. We injected double‐stranded RNA (dsRNA) into third instar larvae of C. maiyasanus. The injection of rn dsRNA resulted in the absence or deformation of the copulatory piece in the male genitalia, which is a characteristic part playing a role in species‐specific genital coupling between the sexes. In addition, the rn dsRNA injection resulted in shortened elytra in both sexes, which is related to the known role of rn in forewing formation in Drosophila. Our study suggests that rn plays a previously underappreciated role in male genital development and potentially contributes to genital diversity in this beetle group.

Selection on an antagonistic behavioral trait can drive rapid genital coevolution in the burying beetle, Nicrophorus vespilloides.

Male and female genital morphology varies widely across many taxa, and even among populations. Disentangling potential sources of selection on genital morphology is problematic because each sex is predicted to respond to adaptations in the other due to reproductive conflicts of interest. To test how variation in this sexual conflict trait relates to variation in genital morphology we used our previously developed artificial selection lines for high and low repeated mating rates. We selected for high and low repeated mating rates using monogamous pairings to eliminate contemporaneous female choice and male–male competition. Male and female genital shape responded rapidly to selection on repeated mating rate. High and low mating rate lines diverged from control lines after only 10 generations of selection. We also detected significant patterns of male and female genital shape coevolution among selection regimes. We argue that because our selection lines differ in sexual conflict, these results support the hypothesis that sexually antagonistic coevolution can drive the rapid divergence of genital morphology. The greatest divergence in morphology corresponded with lines in which the resolution of sexual conflict over mating rate was biased in favor of male interests.

Multiple sexual selection pressures drive the rapid evolution of complex morphology in a male secondary genital structure.

The genitalia of internally fertilizing taxa represent a striking example of rapid morphological evolution. Although sexual selection can shape variation in genital morphology, it has been difficult to test whether multiple sexual selection pressures combine to drive the rapid evolution of individual genital structures. Here, we test the hypothesis that both pre- and postcopulatory sexual selection can act in concert to shape complex structural variation in secondary genital morphology. We genetically modified the size and shape of the posterior lobes of Drosophila melanogaster males and tested the consequences of morphological variation on several reproductive measures. We found that the posterior lobes are necessary for genital coupling and that they are also the targets of multiple postcopulatory processes that shape quantitative variation in morphology, even though these structures make no direct contact with the external female genitalia or internal reproductive organs during mating. We also found that males with smaller and less structurally complex posterior lobes suffer substantial fitness costs in competitive fertilization experiments. Our results show that sexual selection mechanisms can combine to shape the morphology of a single genital structure and that the posterior lobes of D.melanogaster are the targets of multiple postcopulatory selection pressures.

Individual Genetic Contributions to Genital Shape Variation between Drosophila simulans and D. mauritiana.

External genitalia are one of the most rapidly evolving morphological features in insects. In the Drosophila melanogaster species subgroup, males possess a nonfertilizing external genital structure, called the posterior lobe, which is highly divergent among even closely related species. A previous study on this subgroup mapped two genomic regions that affect lobe size and four that affect lobe shape differences between D. mauritiana and D. sechellia; none of the regions affected both size and shape. Here, we investigate whether three of these significant regions also affect lobe size and shape differences between the overlapping species pair D. mauritiana and D. simulans. We found that the same three regions of D. mauritiana, previously shown to affect lobe morphology in a D. sechellia genetic background, also affect lobe morphology in a D. simulans genetic background, with one of the regions affecting both size and shape. Two of the regions also affected morphology when introgressed in the reciprocal direction. The overlap of regions affecting genital morphology within related species pairs indicates either that there is a common underlying genetic basis for variation in genital morphology within this species group or that there are multiple adjacent loci with the potential to influence genital morphology.

Gonopodial Structures Revisited: Variation in Genital Morphology Within and Across Four Populations of the Western Mosquitofish (Gambusia affinis) in Texas

Abstract We report on gonopodial structures in the western mosquitofish (Gambusia affinis) including forked distal hooks and presence-absence of the elbow and gap. In addition, we present information on gonopodial variation across the Trinity, San Jacinto, and Brazos river drainages in Texas.

Multiple quantitative trait loci influence intra-specific variation in genital morphology between phylogenetically distinct lines of Drosophila montana

The evolution of animal genitalia has gained renewed interest because of their potential roles during sexual selection and early stages of species formation. Although central to understanding the evolutionary process, knowledge of the genetic basis of natural variation in genital morphology is limited to a very few species. Using an outbred cross between phylogenetically distinct lines of Drosophila montana, we characterized quantitative trait loci (QTLs) affecting the size and shape of the distiphallus, a prominent part of the male intromittent organ. Our microsatellite-based linkage analysis shows that intra-specific variation in the distiphallus involves several QTLs of largely additive effect and that a highly significant QTL co-localizes with the same inversion where we have earlier localized a large QTL for a sexually selected courtship song trait. The latter indicates that inversions can play an important role in shaping the evolution of rapidly evolving traits with a potential influence on speciation.

Male genital morphology influences paternity success in the millipede Antichiropus variabilis

The genitalia of internally fertilizing animals are among the most diverse of all sexual characters. It is currently argued that genitalia evolve rapidly and divergently due to intense post-copulatory sexual selection. If true, male genital morphology should be subject to directional selection, whereby males with particular genital morphologies achieve greater paternity success. There is mounting evidence that male genital morphology can influence competitive fertilization success; however, the form of selection acting on genitalia has rarely been explored. We conducted competitive fertilization experiments using Antichiropus variabilis millipedes. Using microsatellite loci, we determined the paternity of offspring following double matings. The last male to mate had a significant paternity advantage. While no aspect of the behavior of last males was correlated with paternity success, variation in genital morphology did account for variation in last male paternity. Male genitalia were subject to nonlinear selection, with both convex (stabilizing) selection and concave (disruptive) selection acting on genital shape. This is the first study to provide evidence for sperm precedence in a millipede and only the second to document the form of post-copulatory sexual selection operating on male genital morphology. We discuss the implications of our results for the evolution of genitalia in A. variabilis and, more broadly, how our findings relate to alternative theories of genital evolution.

Geographic variation in genital morphology of Ciulfina praying mantids

AbstractGeographic variation in morphological traits is widespread and important to our current understanding of evolutionary processes. Although male genitalia are perhaps the most divergent morphological traits in animals, geographic variation in genital traits has received little attention and the mechanism driving such variation is unclear. The species isolation hypothesis of genital evolution makes explicit predictions about geographic variation in genitalia predicting patterns of genital divergence that reflect the risk of mating with related but incompatible species. The sexual selection and pleiotropy hypotheses, however, predict general levels of geographic variation that reflect divergent sexual selection pressures or genetic drift. To test these predictions, we investigated geographic variation in genital morphology in the praying mantid genus Ciulfina (Mantodea: Liturgusidae) using elliptic Fourier analysis. We found significant levels of geographic variation in the genital morphology of four Ciulfina species irrespective of the relative proximity of different populations to contact zones with other species. These results reject the species isolation hypothesis, and instead support either the sexual selection or pleiotropy hypotheses to explain patterns of genital evolution in this genus.

Sexual Selection and Genital Evolution in Mammals: A Phylogenetic Analysis of Baculum Length

Studies in invertebrate taxa suggest that postcopulatory sexual selection is an important factor in genital evolution. However, despite wide interspecific variation in genital morphology, evidence for an influence of sexual selection on mammalian genitalia is equivocal. Here I conduct phylogenetically controlled comparative analyses across four mammalian orders to assess how one aspect of this variation--male genital length--scales with (a) male body mass and (b) relative testis mass, the latter providing an index of the intensity of sperm competition. In all four orders, baculum (=os penis) length is found to scale only weakly with male body mass. Both baculum and glans penis length in rodents and baculum length in carnivores are found to vary positively with relative testis mass. In contrast, there is no evidence to support an association between baculum length and relative testis mass in either bats or primates. These results suggest that postcopulatory sexual selection influences genital length in at least some mammals, but significant questions remain both as to why selection on the baculum should differ between mammalian groups and as to the precise mechanistic basis through which males benefit from increased genital length.

Sexual Selection and Genital Evolution in Mammals: A Phylogenetic Analysis of Baculum Length

Studies in invertebrate taxa suggest that postcopulatory sexual selection is an important factor in genital evolution. However, despite wide interspecific variation in genital morphology, evidence for an influence of sexual selection on mammalian genitalia is equivocal. Here I conduct phylogenetically controlled comparative analyses across four mammalian orders to assess how one aspect of this variation—male genital length—scales with (a) male body mass and (b) relative testis mass, the latter providing an index of the intensity of sperm competition. In all four orders, baculum (=os penis) length is found to scale only weakly with male body mass. Both baculum and glans penis length in rodents and baculum length in carnivores are found to vary positively with relative testis mass. In contrast, there is no evidence to support an association between baculum length and relative testis mass in either bats or primates. These results suggest that postcopulatory sexual selection influences genital length in at least some mammals, but significant questions remain both as to why selection on the baculum should differ between mammalian groups and as to the precise mechanistic basis through which males benefit from increased genital length.

Sperm competition in Odonata (Insecta): the evolution of female sperm storage and rivals' sperm displacement

AbstractOdonates (dragonflies) are well known for the ability of the males to displace sperm stored in the female's sperm‐storage organs during copulation. By this means, copulating males are able to increase their fertilization success. This ability has been used as an example to illustrate a conflict of interests between the sexes in which males have evolved sperm‐displacement mechanisms whilst females have presumably evolved means to avoid sperm displacement. The present review has four aims: (1) to describe the copulatory mechanisms used during sperm displacement; (2) to analyse the causes of sperm usage patterns; (3) to discuss this information using current hypotheses on conflict between the sexes; and (4) to illuminate topics for further research. Four copulatory mechanisms are described: sperm removal (physical withdrawal of stored sperm), sperm repositioning (‘pushing’ of rival sperm to sites where its use will be least likely), female sensory stimulation to induce sperm ejection, and sperm flushing (displacement of sperm using the copulating male's sperm). Sperm‐precedence studies in Odonata are scarce and their values vary considerably between species. In those species in which sperm displacement is incomplete, the last copulating male obtains a high but variable short‐term fertilization success which decreases with time. Some male and female factors affecting sperm precedence patterns are mentioned: (1) male variation in genital morphology; (2) duration of copulation influenced by the male (the longer the copulation, the more stored sperm displaced); (3) adaptations of the sperm‐storage organs that allow the female to manipulate the sperm she has received (i.e. avoiding sperm displacement, re‐distributing sperm masses, favouring sperm located in certain sites and ejecting sperm after copulation). We suggest that male and female odonates have co‐evolved at the level of genital function with the control of stored sperm as the focus of the conflict. The benefits for males in this co‐evolution lie in maximizing their fertilization success. However, it is not clear what females obtain from storing sperm and making it unreachable during sperm displacement. Two hypothetical benefits that females may obtain for which some evidence has been gathered are genetic diversity and viability genes. It is finally suggested that odonates can become excellent subjects of study for testing current ideas related to sexual conflict and speciation processes through sexual selection.

Morphological difference and reproductive isolation: morphometrics in the millipede Parafontaria tonominea and its allied forms

Thin-plate spline and other multivariate statistical methods were used to examine the variation in genital morphology and body size in 74 populations of the millipede Parafontaria tonominea and its allied forms in central Japan. Although the study populations included nine sympatric pairs of two reproductively isolated forms, the variations in genital morphology and body size observed were continuous across the study group. Analyses of the sympatric pairs using bootstrapping revealed that the degree of morphological difference between sympatric populations varied considerably from pair to pair. These results demonstrate that the degree of difference in genital morphology and body size may not correspond with the establishment of reproductive isolation. Significant correlation in the pattern of geographic variation was observed for many combinations of morphological components. However, it was not possible to detect a significant correlation between morphology and geographic distance in many of the morphological components studied. This study suggests that the incorporation of genital characters in classification should be done carefully, particularly for animal groups with low vagility, such as millipedes.

Morphological difference and reproductive isolation: morphometrics in the millipede Parafontaria tonominea and its allied forms

Thin-plate spline and other multivariate statistical methods were used to examine the variation in genital morphology and body size in 74 populations of the millipede Parafontaria tonominea and its allied forms in central Japan. Although the study populations included nine sympatric pairs of two reproductively isolated forms, the variations in genital morphology and body size observed were continuous across the study group. Analyses of the sympatric pairs using bootstrapping revealed that the degree of morphological difference between sympatric populations varied considerably from pair to pair. These results demonstrate that the degree of difference in genital morphology and body size may not correspond with the establishment of reproductive isolation. Significant correlation in the pattern of geographic variation was observed for many combinations of morphological components. However, it was not possible to detect a significant correlation between morphology and geographic distance in many of the morphological components studied. This study suggests that the incorporation of genital characters in classification should be done carefully, particularly for animal groups with low vagility, such as millipedes.

Geographic Variation in Genital Morphology among Insular and Mainland Populations of Peromyscus maniculatus and Peromyscus oreas

Geographic relationships among insular and mainland populations of deer mice ( Peromyscus maniculatus and P. oreas ) from the Pacific Northwest were assessed by multivariate analyses of morphometric data from bacula and phalli. Individuals examined represent two distinct forms based on number of autosomal arms in standard karyotypes (fundamental number). Results indicate that the two karyotypic groups have significantly different genitalia, with the form with high fundamental numbers (FN = 85–92) being larger than the form with low fundamental numbers (FN = 74–78) in all characters except depth of the dorsal-lappet cleft. This pattern of morphometric differentiation also characterized allopatric and sympatric pairs of the two groups, thus supporting the hypothesis that individuals are referable to two species (high fundamental numbers = P. oreas; low fundamental numbers = P. maniculatus ). The magnitude of differences in genitalia between allopatric and sympatric samples of the two species failed to corroborate the hypothesis that morphologic differences in genitalia may become amplified in sympatry as a mechanism facilitating reproductive isolation.