Genital Variation Research Articles

Rapid Divergent Evolution of Male Genitalia Among Populations of Drosophila buzzatii

Fil: Soto, Ignacio Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Ecologia, Genetica y Evolucion de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecologia, Genetica y Evolucion de Buenos Aires; Argentina

Litoporus iguassuensis (Araneae, Pholcidae): Camouflaged retreat, sexual dimorphism, female color polymorphism, intra-specific genital variation, and description of the male

We describe the previously unknown male of Litoporus iguassuensisMello-Leitão, 1918 and document the exceptional biology of this species: (1) females and juveniles but not adult males construct camouflaged retreats; (2) there is a strong sexual dimorphism involving coloration, leg length, and behavior; (3) females at some localities are color polymorphic, i.e., discontinuously variable within the population. The species, previously only known from Rio de Janeiro, is widely distributed in the Brazilian Atlantic Forest. Among some of the localities studied it shows genital and male cheliceral variation that is here interpreted as being intraspecific. Preliminary molecular data (16S, H3) reveal low p-distances and no significant grouping information, leading us to hypothesize a single variable species rather than two or more species. Finally, we argue that Mello-Leitão's original assignment to Litoporus (instead of Tupigea) may be correct, and discuss the implications: (1) Litoporus may be nested within Mesabolivar and represent a case of evolutionary shift among microhabitats with the correlated morphological changes; (2) extreme sexual dimorphism may be common in Litoporus and may explain the fact that females continue to be unknown in several species (because they were not recognized as being conspecific with the males).

Pedipalp sclerite homologies and phylogenetic placement of the spider genus Stemonyphantes (Linyphiidae, Araneae) and its implications for linyphiid phylogeny

Male secondary genitalia (pedipalps) are useful characters for species discrimination in most spider families. Although efforts have been made to establish pedipalp sclerite homologies, there are still many inconsistencies in their use. The majority of the morphological characters used to reconstruct the linyphiid phylogeny address male genitalic variation; these inconsistencies may affect the phylogeny and our understanding of linyphiid evolution. Stemonyphantes Menge, 1866, has been hypothesised to be sister to all remaining Linyphiidae. However, despite the basal position of Stemonyphantes, its pedipalp sclerite homologies are not well understood and, along with its monophyly, have never been thoroughly tested in a phylogenetic context. We tested the homology of tegular and radical structures of five Stemonyphantes species to the known linyphioid and araneoid sclerites. All minimum-length trees found under all analytical methods used support Stemonyphantes monophyly and its placement as the sister group to all other Linyphiidae. Our study suggests that Stemonyphantes, unlike any other linyphiids, does have homologues of the araneoid median apophysis and conductor. As Stemonyphantes is the sister group of all other linyphiids, resolving its pedipalp sclerite homologies is critical for understanding sclerite homologies and the phylogeny of the entire family.

Genital divergence in sympatric sister snails

A pattern of greater divergence in mating traits between sister-species pairs with overlapping ranges than between allopatric species pairs is expected if reinforcement commonly contributes to speciation. Few large-scale comparative analyses have addressed this prediction, especially for genital form. Here, we show that penial morphology follows the predicted pattern in 40 robustly identified sister-species pairs in the marine gastropod subfamily Littorininae. Further work is needed to exclude other processes that may contribute to genital divergence between sympatric species, but the clear pattern we observe strongly suggests a role for genital form in reproductive isolation in this large clade.

What controls the “genitive variation” in Present-Day English?

This paper takes up the recent discussion of what controls speakers’ use of the -s and of- genitives, as in the university’s budget and the budget of the university. Most of the paper deals directly with control of that “genitive variation”. It first argues that there is a third variant, as in the university budget. It then discusses why all three just given, for example, are grammatical, but, with a litre of petrol, the alternatives (*a petrol’s litre and *a petrol litre) are not grammatical, arguing that the grammaticality is controlled by whether the word and phrase meanings are compatible with their syntax. It then argues that, where there are equally grammatical alternatives, the speakers’ choice often depends on the same issues of semantic and syntactic compatibility. The last main section of the paper deals with the grammatical status of that third variant, arguing that the university budget truly is genitive.

Evolution of reproductive morphology among recently diverged taxa in the Drosophila mojavensis species cluster.

The morphological evolution of sexual traits informs studies of speciation due to the potential role of these characters in reproductive isolation. In the current study, we quantified and compared genitalic variation within the Drosophila mojavensis species cluster to infer the mode of evolution of the male aedeagus. This system is ideal for such studies due to the opportunity to test and compare levels of variation along a divergence continuum at various taxonomic levels within the group. Shape variation was quantified using elliptic Fourier descriptors and compared among the four D. mojavensis host races, and between D. mojavensis and its sister species Drosophila arizonae. Aedeagus shape was diagnostic for D. arizonae, and among three of the four D. mojavensis subspecies. In each of these cases, there was less variation within subspecies than among subspecies, which is consistent with the pattern predicted if genitalia are evolving according to a punctuated change model, and are involved with mate recognition. However, aedeagus shape in Drosophila mojavensis sonorensis was highly variable and broadly overlapping with the other three subspecies, suggesting aedeagus evolution in this subspecies is more complex and subject to additional evolutionary factors. These results are interpreted and discussed in the context of selection on mate recognition systems and the potential for failed copulation.

Shape - but Not Size - Codivergence between Male and Female Copulatory Structures in Onthophagus Beetles

Genitalia are among the fastest evolving morphological traits in arthropods. Among the many hypotheses aimed at explaining this observation, some explicitly or implicitly predict concomitant male and female changes of genital traits that interact during copulation (i.e., lock and key, sexual conflict, cryptic female choice and pleiotropy). Testing these hypotheses requires insights into whether male and female copulatory structures that physically interact during mating also affect each other's evolution and patterns of diversification. Here we compare and contrast size and shape evolution of male and female structures that are known to interact tightly during copulation using two model systems: (a) the sister species O. taurus (1 native, 3 recently established populations) and O. illyricus, and (b) the species-complex O. fracticornis-similis-opacicollis. Partial Least Squares analyses indicated very little to no correlation between size and shape of copulatory structures, both in males and females. Accordingly, comparing shape and size diversification patterns of genitalia within each sex showed that the two components diversify readily - though largely independently of each other - within and between species. Similarly, comparing patterns of divergence across sexes showed that relative sizes of male and female copulatory organs diversify largely independent of each other. However, performing this analysis for genital shape revealed a signature of parallel divergence. Our results therefore suggest that male and female copulatory structures that are linked mechanically during copulation may diverge in concert with respect to their shapes. Furthermore, our results suggest that genital divergence in general, and co-divergence of male and female genital shape in particular, can evolve over an extraordinarily short time frame. Results are discussed in the framework of the hypotheses that assume or predict concomitant evolutionary changes in male and female copulatory organs.

Experiments with genitalia: a commentary

There has been a recent burst of studies of the function of genitalia, many of which share several important shortcomings. Given that further studies on this topic are likely (there are probably millions of species showing rapid genital divergence), I discuss the studies critically to promote clear formulation of hypotheses and interpretation of results in the future. I also emphasize some possibly important but neglected variables, including female stimulation, phylogenetic contexts, and the behavior of male genitalia, and outline simple techniques that could improve future studies.

Genitalic variation and taxonomic discrimination in the semi-aquatic spider genus Paratrechalea (Araneae: Trechaleidae)

For spiders, morphological differentiation within genitalic traits is the main diagnostic criterion of a species. Beside some well-described exceptions of genitalic polymorphism and crypticity, spider genitalic variation is seldom quantitatively analyzed. Using geometric morphometrics landmark analysis, we report clear evidence of quantitative interspecific divergence and intraspecific variation in the genital shape of three species of the genus Paratrechalea (P. azul, P. ornata and P. galianoae). The genitalic species recognition was very consistent with our quantitative data for both sexes. Interspecific variation suggested a character displacement pattern between two syntopic populations of P. azul and P ornata, and also a possible case of species crypticity in P. ornata that will involve splitting the Uruguayan populations from the Brazilian ones.

On the pseudoterrestris species group of the spider genus Coelotes (Araneae, Amaurobiidae)

Nine species of the spider genus Coelotes are described from China and Thailand, and assigned to the pseudoterrestris species group. Six of the species are described from both sexes (Coelotes acicularis sp. nov., C. guangxian Zhang et al. 2003, C. pseudoterrestris Schenkel 1963, C. pseudoyunnanensis sp. nov., C. suthepicus Dankittipakul, Chami-Kranon & Wang 2005 and C. thailandensis Dankittipakul & Wang 2003) and three from the female only (C. pseudoguangxian sp. nov., C. yunnanensis Schenkel 1963 and C. yanhengmei sp. nov.). Significant morphological variation in the epigynum and vulva was found in C. pseudoterrestris, a species widespread from eastern to western Yunnan. The combination of significant genitalic variation and widespread occurrence suggest that C. pseuduterrestris may be a cryptic species complexs, but this hypothesis needs to be justified by further collection of both male and female specimens from other localities.

Taxonomic revision of the Mecyclothorax beetles (Coleoptera: Carabidae) of Oahu: epithets as epitaphs for an endangered fauna?

Abstract.The Mecyclothorax Sharp beetle fauna of Oahu, Hawaii is revised, including the description of 13 new species—M. acherontius, M. uncinus, M. lobatus, M. dentatus, M. calceus, M. euryoides, M. invictus, M. ovatulus, M. lemur, M. satyrus, M. ramsdalei, M. pelops and M. niobespp.n.—to complement the six previously described species. Several cryptic species complexes characterized by similar external anatomy and highly divergent male genitalia are present in the fauna, including the M. brevis (Blackburn) species complex—four species sympatrically distributed on Tantalus, a mountain on the northern margin of Honolulu—and the sympatric sister species M. carteri (Perkins) and M. invictus from Mt. Kaala in the western Waianae Range. This repeated pattern of closely related species characterized by divergent male genitalia and relatively static external anatomy is also observed in the Mecyclothorax fauna of Molokai, an island of moderate geologic age within the Hawaiian archipelago, but not in the Mecyclothorax fauna of the most recently emergent Hawaii Island. Species distributions are generally also much more restricted on the older islands. These results are consistent with the occurrence of rampant, unfixed infraspecific genitalic variation early in an island radiation, with subsequent fixation of divergent genitalic characters occurring as speciation proceeds. Three distinct areas of endemism are defined by distributions of Oahu Mecyclothorax: the Waianae Range, the north Koolau Range and the south Koolau Range. Species distributions in two other carabid beetle genera in Hawaii containing native species—Blackburnia Sharp and Bembidion Latreille—congruently define these areas. The historical range of sampling dates is compared for Mecyclothorax species across the three areas, with the greatest diminution of recently collected species‐level diversity characterizing the south Koolau Range, where several Mecyclothorax species are characterized both by restricted geographic distributions within the developmental footprint of Honolulu, and by a lack of recent field collections, suggesting that they may qualify for endangered species status.

Assessment of rampant genitalic variation in the spider genus Homalonychus (Araneae, Homalonychidae)

Abstract. Animal genitalia are often complex and thought to vary little within species but differ between closely related species making them useful as primary characters in species diagnosis. Spiders are no exception, with nearly all of the 40,462 (at the time of this writing) described species differentiated by genitalic characteristics. However, in some cases, the genitalia of putative species are not uniform, but rather vary within species. When intraspecific variation overlaps interspecific variation, it can be difficult (if not impossible) to place a name on a specimen. The quantification of shape variation in genitalia has not often been attempted, probably because until recently it was not a methodologically and computationally simple process. In the two currently recognized species of the spider genus Homalonychus, genitalic variation is rampant in both male and female structures, with some parts of the genitalia (e.g., the retrolateral tibial apophysis) differing in each specimen examined. In this study, geometric morphometric analysis employing landmark data is used to quantify both intra‐ and interspecific variation in this genus. The large amount of variation is condensed into two or three groups depending on the structures examined, and these groups correspond to either the two species or to previously established mitochondrial DNA clades within one of the species. The results also show that analyses of female structures do not separate the groups as readily as the analyses of the male structures. The large amount of variation present in some structures is not correlated with geography or population genetic structure.

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.

Revision von Oxychilus diaphanellus (Krynicki, 1836) aus der Krim (Gastropoda: Stylommatophora: Zonitidae)

1. Professor dr hab. Adolf Riedel February 24th 1930 - August 21st 2010 Andrzej Wiktor, Ewa Stworzewicz, Dominika Mierzwa Folia Malacologica CrossRef

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.

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.

RAPID ANTAGONISTIC COEVOLUTION BETWEEN PRIMARY AND SECONDARY SEXUAL CHARACTERS IN HORNED BEETLES

Different structures may compete during development for a shared and limited pool of resources to sustain growth and differentiation. The resulting resource allocation trade-offs have the potential to alter both ontogenetic outcomes and evolutionary trajectories. However, little is known about the evolutionary causes and consequences of resource allocation trade-offs in natural populations. Here, we explore the significance of resource allocation trade-offs between primary and secondary sexual traits in shaping early morphological divergences between four recently separated populations of the horned beetle Onthophagus taurus as well as macroevolutionary divergence patterns across 10 Onthophagus species. We show that resource allocation trade-offs leave a strong signature in morphological divergence patterns both within and between species. Furthermore, our results suggest that genital divergence may, under certain circumstances, occur as a byproduct of evolutionary changes in secondary sexual traits. Given the importance of copulatory organ morphology for reproductive isolation our findings begin to raise the possibility that secondary sexual trait evolution may promote speciation as a byproduct. We discuss the implications of our results on the causes and consequences of resource allocation trade-offs in insects.

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.

Taxonomic revision of Mecyclothorax Sharp (Coleoptera, Carabidae) of Hawaii Island: abundant genitalic variation in a nascent island radiation

The Hawaii Island fauna of Mecyclothorax Sharp, 1903 is taxonomically revised and found to comprise 30 species, 18 newly described: M. gagnei sp. n., M. nitidus sp. n., M. maunakukini sp. n., M. punakukini sp. n., M. kaukukini sp. n., M. perivariipes sp. n., M. aa sp. n., M. giffini sp. n., M. hephaestus sp. n., M. funebris sp. n., M. granulipennis sp. n., M. rufipennis sp. n., M. blackburnianus sp. n., M. swezeyi sp. n., M. sinuosus sp. n., M. williamsi sp. n., M. purpuripennis sp. n., and M. footei sp. n. New synonymies include: Mecyclothorax parvus Britton, 1948 = M. subunctus (Perkins), 1917; Thriscothorax munroi Perkins, 1937 = M. karschi (Blackburn), 1882; Thriscothorax gracilis Sharp, 1903 and Mecyclothorax proximus Britton, 1948 = M. konanus Sharp, 1903; Mecyclothorax terminalis Britton, 1948 = M. discedens (Sharp) 1903. Mecyclothorax vulcanus (Blackburn) was described from a mixed series, with the cryptic sibling species M. hephaestus newly described to correct the partial misidentification. Species delimitation for the highly variable M. konanus is achieved using a hierarchical analysis based on infraspecifically variable attributes. Extensive male genitalic variation is documented within M. konanus and M. deverilli (Blackburn), and also among the cryptic sibling species pair M. variipes (Blackburn) and M. perivariipes. The observed variation is consistent with various hypotheses of sexual selection, but not with the genitalic lock and key hypothesis. Areas of endemism are tentatively proposed based on the most restricted distributions of Hawaii Island Mecyclothorax, with various flanks of Mauna Kea and Mauna Loa volcanoes identified as distinctive areas. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Recent changes in the function and frequency of Standard English genitive constructions: a multivariate analysis of tagged corpora

This study of present-day English genitive variation is based on all interchangeable instances of s- and of-genitives from the ‘Reportage’ and ‘Editorial’ categories of the ‘Brown family’ of corpora. Variation is studied by tapping into a number of independent variables, such as precedence of either construction in the text, length of the possessor and possessum phrases, phonological constraints, discourse flow, and animacy of the possessor. In addition to distributional analyses, we use logistic regression to investigate the probabilistic factor weights of these variables, thus tracking language change in progress as evidenced in the language of the press. This method, married to our large database, yields the most detailed perspective to date on frequently discussed issues, such as the relative importance of possessor animacy and end-weight in genitive choice (cf. most recently Rosenbach 2005), or on the exact factorial dynamics responsible for the ongoing spread of the s-genitive.