Size and shape interspecific divergence patterns partly reflect phylogeny in an Onthophagus species‐complex (Coleoptera: Scarabaeidae)

Polyphenism has been suggested as an accelerator for morphological evolution and speciation. In the dung beetles of the genus Onthophagus, horn expression is polyphenic: large males develop horns whereas smaller males express greatly reduced or no horns. Horn static allometries seem to diverge rapidly amongst extant taxa, a process which might trigger changes in the male genital morphology, thus possibly promoting speciation as a by‐product. It can therefore be hypothesized that interspecific distances in allometries and, possibly, in other morphological traits mirror phylogenetic distances. In this study we first assessed the phylogenetic relationships amongst three closely related taxa belonging to the so‐called ‘Onthophagus fracticornis‐similis‐opacicollis’ species‐complex by sequencing the mitochondrial gene cytochrome oxidase subunit 1 (cox1). Biomolecular results indicated three independent lineages, the closest relationships being found between Onthophagus similis and Onthophagus opacicollis. Then we assessed the extent to which divergence pattern of horn static allometries and size and shape divergence patterns of one genital (paramere) and two nongenital (head and epipharynx) structures mirrored the phylogenetic relationships. Interspecific divergence patterns of horn static allometries, paramere, and head shape were found to be congruent with the evolutionary relationships inferred from biomolecular data. Nevertheless, paramere size and epipharynx shape showed patterns not consistent with the phylogeny. Furthermore, the relative size of nongenital structures showed little interspecific divergence compared to their shapes. Our results suggest that size and shape interspecific divergence mirror phylogeny only in part; they also indicate that distinct morphological traits may differ in their tendency to evolve in concert, and that size and shape of the same trait can evolve independently across species. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162 , 482–498.     

Sexual selection targets cetacean pelvic bones

Male genitalia evolve rapidly, probably as a result of sexual selection. Whether this pattern extends to the internal infrastructure that influences genital movements remains unknown. Cetaceans (whales and dolphins) offer a unique opportunity to test this hypothesis: since evolving from land‐dwelling ancestors, they lost external hind limbs and evolved a highly reduced pelvis that seems to serve no other function except to anchor muscles that maneuver the penis. Here, we create a novel morphometric pipeline to analyze the size and shape evolution of pelvic bones from 130 individuals (29 species) in the context of inferred mating system. We present two main findings: (1) males from species with relatively intense sexual selection (inferred by relative testes size) tend to evolve larger penises and pelvic bones compared to their body length, and (2) pelvic bone shape has diverged more in species pairs that have diverged in inferred mating system. Neither pattern was observed in the anterior‐most pair of vertebral ribs, which served as a negative control. This study provides evidence that sexual selection can affect internal anatomy that controls male genitalia. These important functions may explain why cetacean pelvic bones have not been lost through evolutionary time.     

Slow genital and genetic but rapid non-genital and ecological differentiation in a pair of spider species (Araneae,Pholcidae)

Like most animals with internal fertilization, spiders tend to have species-specific genitalia, allowing closely related species to be identified by their reproductive morphology more easily than by non-genital characters. This implies that genitalia evolve on average more rapidly than non-genital morphological traits. Here we describe two putative species of Pholcidae from Taiwan (Pholcus pingtung, n. sp.; Pholcus chengpoi, n. sp.) that differ conspicuously in their microhabitat (rocks vs. leaves), coloration, color pattern, and body proportions, but have almost indistinguishable genitalia and cytochrome oxidase I (co1) sequences. The two species have identical yet highly unusual male cheliceral modifications, strongly arguing for sister species. Despite the almost identical genitalia and co1 sequences, we treat the two ‘morphs’ as species for three reasons: (1) they are easily distinguished by several characters; no intermediate specimens were found; (2) subtle yet consistent differences in genital (uncus) shape support the idea of reproductively isolated entities beyond the more conspicuous non-genital differences; (3) each locality provided both types of microhabitat but only one of the two species, arguing against environmental plasticity or polymorphism. We conclude that probably a very recent expansion into a novel microhabitat has led to speciation and rapid ecological and non-genital differentiation, with insufficient time to accumulate significant genital and genetic differences.     

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.     

Divergence in genital morphology may contribute to mechanical reproductive isolation in a millipede

Genitalia appear to evolve rapidly and divergently in taxa with internal fertilization. The current consensus is that intense directional sexual selection drives the rapid evolution of genitalia. Recent research on the millipede Antichiropus variabilis suggests that the male genitalia are currently experiencing stabilizing selection – a pattern of selection expected for lock‐and‐key structures that enforce mate recognition and reproductive isolation. Here, we investigate how divergence in genital morphology affects reproductive compatibility among isolated populations of A. variabilis. Females from a focal population were mated first to a male from their own population and, second, to a male from one of two populations with divergent genital morphology. We observed variation in mating behavior that might indicate the emergence of precopulatory reproductive barriers: males from one divergent population took significantly longer to recognize females and exhibited mechanical difficulty in genital insertion. Moreover, we observed very low paternity success for extra‐population males who were successful in copulating. Our data suggest that divergence in genital shape may be contributing to reproductive isolation, and incipient speciation among isolated populations of A. variabilis.     

Molecular phylogeny reveals high diversity and endemism in the limestone karst-restricted land snail genus Sophina Benson, 1859 from Myanmar (Eupulmonata: Helicarionidae), with description of four new species

Sophina is a poorly known and neglected genus due to the inaccessibility of the Salween Basin, Southern Myanmar. Taxonomic status, distribution, and phylogeny are being revised based on an integrative analysis of genitalia, radula, and molecular data. Morphological variation in shells and genitalia, together with a phylogenetic tree from concatenated data of mitochondrial and nuclear genes, revealed the existence of ten species/subspecies. Penial morphology and genetic divergence were generally consistent and useful in delimiting species, while shell characters showed little overall taxonomic utility in some species. Taxonomic placement of the previous subspecies “bensoni” shows clear distinction in both genitalia and molecular evidence, and is currently recognized as a distinct species. The nominal species “S. schistostelis” and “S. calias” possess similar genitalia and shell morphology, and molecular evidence suggested that they are sister taxa representing geographically isolated populations. Four new species are additionally described herein as S. furfuracea n. sp., S. pisinna n. sp., S. salweenica n. sp., and S. tonywhitteni n. sp. based on both morphology and molecular evidence. Phylogenetic analyses supported monophyly of Sophina, and further a split into two principal clades. These two clades showed little difference in genitalia, but more clear differences in the umbilical area and allopatric distribution in upper and lower reaches of the Gyaing River. High genetic divergence was revealed and this coincided with remarkable degree of endemism and localization with a pattern of one outcrop for one lineage. These data highlight the importance of the Salween Basin's karst ecosystems as an evolutionary and endemic biodiversity hotspot, and indicate that a focus on conservation and management in this area is urgently required.     

Evolution of the elaborate male intromittent organ of Xiphophorus fishes

Internally fertilizing animals show a remarkable diversity in male genital morphology that is associated with sexual selection, and these traits are thought to be evolving particularly rapidly. Male fish in some internally fertilizing species have “gonopodia,” highly modified anal fins that are putatively important for sexual selection. However, our understanding of the evolution of genital diversity remains incomplete. Contrary to the prediction that male genital traits evolve more rapidly than other traits, here we show that gonopodial traits and other nongonopodial traits exhibit similar evolutionary rates of trait change and also follow similar evolutionary models in an iconic genus of poeciliid fish (Xiphophorus spp.). Furthermore, we find that both mating and nonmating natural selection mechanisms are unlikely to be driving the diverse Xiphophorus gonopodial morphology. Putative holdfast features of the male genital organ do not appear to be influenced by water flow, a candidate selective force in aquatic habitats. Additionally, interspecific divergence in gonopodial morphology is not significantly higher between sympatric species, than between allopatric species, suggesting that male genitals have not undergone reproductive character displacement. Slower rates of evolution in gonopodial traits compared with a subset of putatively sexually selected nongenital traits suggest that different selection mechanisms may be acting on the different trait types. Further investigations of this elaborate trait are imperative to determine whether it is ultimately an important driver of speciation.     

Genital morphology of female goblin spiders (Arachnida: Araneae: Oonopidae) with functional implications

Spider genital morphology usually provides the best characters for taxonomy. Furthermore, functional genital morphology helps to understand the evolution of complex genitalia and their role in the context of sexual selection. The genital systems of most haplogyne spider families are poorly investigated with respect to their morphology. The present study investigates the female genitalia of the oonopids Oonops pulcher, Oonopinus kilikus, and Pseudotriaeris sp. by means of light microscopy and SEM. The male palps are briefly described. Females of O. pulcher store spermatozoa in an anterior and a posterior receptaculum (PRe). The genitalia resemble the primitive dysderoid genitalia supporting the hypothesis that the subfamily Oonopinae contains more basal oonopids. In O. kilikus, the anterior receptaculum is reduced to a sclerite. Spermatozoa are stored in a PRe. The receptacula of Pseudotriaeris sp. are reduced to sclerites. Spermatozoa in the uterus internus indicate that fertilization happens there or in the ovary. The anterior sclerite might serve females to lock the uterus during copulation as suggested for other gamasomorphines. The male palp of O. kilikus is simple, whereas the palps of O. pulcher and Pseudotriaeris sp. appear more complex. Complicated structures on the palp of Pseudotriaeris sp. indicate that males exert copulatory courtship.     

Revision of the Neotropical Genus Hemibidessus Zimmermann (Coleoptera: Dytiscidae: Hydroporinae: Bidessini)

The genus Hemibidessus Zimmermann, 1921 is revised. Six species are recognized in the genus. Two new species are described, H. spirodiscus sp. n. from Bolivia and H. spangleri sp. n. from Argentina. A key for identifying the species is presented. The female genitalia are thoroughly illustrated and described for the first time for any species of Bidessini. Other important diagnostic structures are also illustrated including the male genitalia. A cladistic analysis is presented for 8 species (6 ingroup and 2 outgroup species) and 13 characters. A single most parsimonious cladogram was found.     

Sex combs,allometry, and asymmetry in Drosophila

There has been recent debate about the expected allometry of sexually‐selected traits. Although sexually‐selected traits exhibit a diversity of allometric patterns, signalling characters are frequently positively allometric. By contrast, insect genitalia tend to be negatively allometric, although the allometry of nongenital sexually‐selected characters in insects is largely unknown (with some notable exceptions). It has also been suggested that there should be a negative association between the asymmetry and size of bilaterally‐paired, sexually‐selected traits, although this claim is controversial. We assessed the allometry and asymmetry (fluctuating asymmetry, FA) of a nongenital contact–courtship structure, the sex comb, in replicate populations of three species of Drosophila (we also measured wing FA). Sex combs are sexually‐selected characters used to grasp the female's abdomen and genitalia and to spread her wings prior to and during copulation. Although species differed in the size of the sex combs, all combs were positively allometric, and comb allometry did not generally differ significantly between species or populations. Comb and wing asymmetry did vary across species, although not across populations of the same species. However, FA was trait specific and was never negatively associated with trait size. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 923–934.     

Molecular phylogeny reveals the repeated evolution of complex male genital traits in the New Zealand moth genus Izatha (Lepidoptera: Xyloryctidae)

Male genitalia are among the most rapidly evolving and divergent morphological structures and sexual selection is known to drive this phenomenon in many taxa. Because of their diversity, even within a single genus, genital characters are frequently used to infer relationships among closely‐related species. Moths within the genus Izatha (Xyloryctidae) are ideal candidates for investigating the phylogenetic patterns of genital evolution as they display great variation in male genital structure and complexity. We determined the evolutionary relationships among 31 species of Izatha by constructing a molecular phylogeny of the genus based on the mitochondrial cytochrome oxidase subunit I gene and the isocitrate dehydrogenase and carbamoylphosphate synthase domain protein nuclear genes. This allowed estimations of ancestral male genital character states and patterns of male genital diversification using maximum‐likelihood models. The genus is divided into two well‐supported clades and two poorly supported clades at the root of the phylogeny with incomplete phylogenetic resolution within two species groups, likely due to rapid speciation. Izatha display a number of apomorphic phallic traits including cornuti (sclerotized spines) which are either discharged into the female during copulation (deciduous cornuti) or fixed to the male phallus (compound and fish‐hook cornuti). Within the genus, there is a reduction of secondary genital characters – the uncus and gnathos – but an elaboration of another grasping structure, the juxta; the potential origin and functionality of these male genital traits are discussed. Overall, some male genital characters provided a good indication of species relationships; however, several parts of the complex male genitalia of Izatha show evidence of homoplasy and convergence highlighting the problems of using these traits in determining species relationships. Additionally, this convergence has highlighted that complex genital structures may evolve repeatedly and independently within a lineage.     

Phenotypic and genetic variation in male genitalia in the seedbug, Lygaeus equestris (Heteroptera)

Male genitalia evolve through sexual selection and, in insects, tend to show negative static allometry, low phenotypic variation, and are usually relatively small. Much less is known about the genetic variation and heritability of male genitalia. Additionally, in instances where the intromittent organ is greatly elongated, it is unclear whether typical patterns of genital scaling and variation also apply. In the present study, we investigated the allometry, variation, and heritability of male genital length in the seedbug, Lygaeus equestris , a species with a greatly elongated intromittent organ (i.e. almost as long as male body size). We found that genital length was negatively allometric, in spite of its great length, and was no more variable than nongenital traits. Additionally, genital length was significantly heritable and had considerable evolvability.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 400–405.     

Mosaic pattern of genital divergence in three populations of Schistocerca lineata Scudder, 1899 (Orthoptera: Acrididae: Cyrtacanthacridinae)

Sexual selection theory predicts that genital structures in isolated populations are likely to diverge, but male genitalia are often species-specific, which led to the idea that male genitalia are relatively invariable within species. Previous allometric studies collectively suggested that male genitalia are intraspecifically invariable in size compared with external body parts. We investigated whether male genitalia are invariable in shape in three populations of a grasshopper Schistocerca lineata Scudder, 1899, using two independent methods of geometric morphometric analyses. Specifically, we focused on the idea that male genitalia are complex structures consisting of many functionally different components, and studied how these individual parts diverge among three populations. Individual components of male genitalia show different population-level divergence, resulting in the mosaic pattern of genital divergence. Individual components diverge independently from each other. Body size is positively correlated with genitalia size, but is significantly correlated with the shape of only one of the three genital structures we measured. Thus, different components of male genitalia may be influenced by different evolutionary processes. This study is the first to show that components of complex genitalia evolve separately within a species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 289–301.     

Small but not ephemeral: newly discovered species of Aphelinidae and Trichogrammatidae (Insecta: Hymenoptera: Chalcidoidea) from Eocene amber

New species of fossil Aphelinidae and Trichogrammatidae are described from middle Eocene (Lutetian) Baltic amber (41.3–47.8 Ma). A new subfamily, two new genera and three new species of Aphelinidae are described, with comments on their placement: Phtuaria fimbriae gen.n. , sp.n. in Phtuariinae subf.n. , Glaesaphytis interregni gen.n. , sp.n. and Centrodora brevispinae sp.n. These represent the first described true fossil Aphelinidae. Four new species of Trichogrammatidae are described: Mirufens illusionis sp.n. , Palaeogramma eos gen.n. , sp.n. , Pterandrophysalis plasmans sp.n. and Szelenyia terebrae sp.n. , thus expanding our knowledge of fossil Trichogrammatidae beyond the single previously described species. The presence of recognizable extant genera of Aphelinidae and Trichogrammatidae in the Eocene suggests that the morphology of these genera has been relatively invariant despite highly variable conditions during and since the Eocene. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:E9AD60B6‐3D56‐4E74‐AA54‐F7B91F4FDC79 .     

The function and evolution of male and female genitalia in Phyllophaga Harris scarab beetles (Coleoptera: Scarabaeidae)

Genitalia diversity in insects continues to fuel investigation of the function and evolution of these dynamic structures. Whereas most studies have focused on variation in male genitalia, an increasing number of studies on female genitalia have uncovered comparable diversity among females, but often at a much finer morphological scale. In this study, we analysed the function and evolution of male and female genitalia in Phyllophaga scarab beetles, a group in which both sexes exhibit genitalic diversity. To document the interaction between male and female structures during mating, we dissected flash‐frozen mating pairs from three Phyllophaga species and investigated fine‐scale morphology using SEM. We then reconstructed ancestral character states using a species tree inferred from mitochondrial and nuclear loci to elucidate and compare the evolutionary history of male and female genitalia. Our dissections revealed an interlocking mechanism of the female pubic process and male parameres that appears to improve the mechanical fit of the copulatory position. The comparative analyses, however, did not support coevolution of male and female structures and showed more erratic evolution of the female genitalia relative to males. By studying a group that exhibits obvious female genitalic diversity, we were able to demonstrate the relevance of female reproductive morphology in studies of male genital diversity.     

Taxonomic position of the cricket genus Eneopteroides Chopard, 1956 (Orthoptera: Grylloidea,Podoscirtidae), with descriptions of two new species

The cricket genus Eneopteroides Chopard, 1956 is transferred from the Eneopteridae to the Podoscirtidae owing to characters in external morphology and male genitalia. One species initially described in the genus Aphonomorphus Rehn, 1903, A. bicolor Hebard, 1928b, is transferred to Eneopteroides and two new species from western Amazonia are described, E. loretensis n. sp. and E. cordobensis n. sp.     

Demonstrating sexual selection by cryptic female choice on male genitalia: What is enough?

Rapid divergence in external genital structures occurs in nearly all animal groups that practice internal insemination; explaining this pattern is a major challenge in evolutionary biology. The hypothesis that species‐specific differences in male genitalia evolved under sexual selection as courtship devices to influence cryptic female choice (CFC) has been slow to be accepted. Doubts may stem from its radical departure from previous ideas, observational difficulties because crucial events occur hidden within the female's body, and alternative hypotheses involving biologically important phenomena such as speciation, sperm competition, and male‐female conflicts of interest. We assess the current status of the CFC hypothesis by reviewing data from two groups in which crucial predictions have been especially well‐tested, Glossina tsetse flies and Roeseliana (formerly Metrioptera) roeselii bushcrickets. Eighteen CFC predictions have been confirmed in Glossina and 19 in Roeseliana. We found data justifying rejection of alternative hypotheses, but none that contradicted CFC predictions. The number and extent of tests confirming predictions of the CFC hypothesis in these species is greater than that for other generally accepted hypotheses regarding the functions of nongenital structures. By this criterion, it is reasonable to conclude that some genital structures in both groups likely involved sexual selection by CFC.