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Fine-scale genital morphology affects male ejaculation success: an experimental test.

ABSTRACT: The evolution of male genital traits is usually ascribed to advantages that arise when there is sperm competition, cryptic female choice or sexual conflict. However, when male-female contact is brief and sperm production is costly, genital structures that ensure the appropriate timing of sperm release should also be under intense selection. Few studies have examined the role of individual structures in triggering ejaculation. We therefore conducted a series of anatomical manipulations of fine-scale features of the complex intromittent organ (gonopodium) of a freshwater fish with internal fertilization (Gambusia holbrooki) to determine their effects on sperm release. Mating in G. holbrooki is fleeting (less than 50 ms), so there should be strong selection for control over the timing of sperm release. We surgically removed three features at the tip of the gonopodium (claws, spines, awl-shape) to test for their potential role in triggering ejaculation. We show that the 'awl-shape' of the tip affects sperm release when a male makes contact with a female, but neither gonopodial claws nor spines had a detectable effect. We suggest that the claws and spines may instead function to increase the precision of sperm deposition (facilitating anchorage and contact time with the female's gonopore), rather than the initiation of ejaculation.

SUBMITTER: Chung MJ

PROVIDER: S-EPMC7336860 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Male genital lobe morphology affects the chance to copulate in Drosophila pachea.

Project description:IntroductionMale genitalia are thought to ensure transfer of sperm through direct physical contact with female during copulation. However, little attention has been given to their pre-copulatory role with respect to sexual selection and sexual conflict. Males of the fruitfly Drosophila pachea have a pair of asymmetric external genital lobes, which are primary sexual structures and stabilize the copulatory complex of female and male genitalia. We wondered if genital lobes in D. pachea may have a role before or at the onset of copulation, before genitalia contacts are made.ResultsWe tested this hypothesis with a D. pachea stock where males have variable lobe lengths. In 92 mate competition trials with a single female and two males, females preferentially engaged into a first copulation with males that had a longer left lobe and that displayed increased courtship vigor. In 53 additional trials with both males having partially amputated left lobes of different lengths, we observed a weaker and non-significant effect of left lobe length on copulation success. Courtship durations significantly increased with female age and when two males courted the female simultaneously, compared to trials with only one courting male. In addition, lobe length did not affect sperm transfer once copulation was established.ConclusionLeft lobe length affects the chance of a male to engage into copulation. The morphology of this primary sexual trait may affect reproductive success by mediating courtship signals or by facilitating the establishment of genital contacts at the onset of copulation.

| S-EPMC7877081 | biostudies-literature

Male genital morphology and its influence on female mating preferences and paternity success in guppies.

Project description:In internally fertilizing species male genitalia often show a higher degree of elaboration than required for simply transferring sperm to females. Among the hypotheses proposed to explain such diversity, sexual selection has received the most empirical support, with studies revealing that genital morphology can be targeted by both pre-and postcopulatory sexual selection. Until now, most studies have focused on these two episodes of selection independently. Here, we take an alternative approach by considering both components simultaneously in the livebearing fish, Poecilia reticulata. We allowed females to mate successively (and cooperatively) with two males and determined whether male genital length influenced the female's propensity to mate with a male (precopulatory selection, via female choice) and whether male genital size and shape predicted the relative paternity share of subsequent broods (postcopulatory selection, via sperm competition/cryptic female choice). We found no evidence that either episode of sexual selection targets male genital size or shape. These findings, in conjunction with our recent work exposing a role of genital morphology in mediating unsolicited (forced) matings in guppies, further supports our prior speculation that sexual conflict may be an important broker of genital evolution in this species.

| S-EPMC3142123 | biostudies-literature

Coevolution of male and female genital morphology in waterfowl.

Project description:Most birds have simple genitalia; males lack external genitalia and females have simple vaginas. However, male waterfowl have a phallus whose length (1.5->40 cm) and morphological elaborations vary among species and are positively correlated with the frequency of forced extra-pair copulations among waterfowl species. Here we report morphological complexity in female genital morphology in waterfowl and describe variation vaginal morphology that is unprecedented in birds. This variation comprises two anatomical novelties: (i) dead end sacs, and (ii) clockwise coils. These vaginal structures appear to function to exclude the intromission of the counter-clockwise spiralling male phallus without female cooperation. A phylogenetically controlled comparative analysis of 16 waterfowl species shows that the degree of vaginal elaboration is positively correlated with phallus length, demonstrating that female morphological complexity has co-evolved with male phallus length. Intersexual selection is most likely responsible for the observed coevolution, although identifying the specific mechanism is difficult. Our results suggest that females have evolved a cryptic anatomical mechanism of choice in response to forced extra-pair copulations.

| S-EPMC1855079 | biostudies-literature

tartan underlies the evolution of Drosophila male genital morphology.

Project description:Male genital structures are among the most rapidly evolving morphological traits and are often the only features that can distinguish closely related species. This process is thought to be driven by sexual selection and may reinforce species separation. However, while the genetic bases of many phenotypic differences have been identified, we still lack knowledge about the genes underlying evolutionary differences in male genital organs and organ size more generally. The claspers (surstyli) are periphallic structures that play an important role in copulation in insects. Here, we show that divergence in clasper size and bristle number between Drosophila mauritiana and Drosophila simulans is caused by evolutionary changes in tartan (trn), which encodes a transmembrane leucine-rich repeat domain protein that mediates cell-cell interactions and affinity. There are no fixed amino acid differences in trn between D. mauritiana and D. simulans, but differences in the expression of this gene in developing genitalia suggest that cis-regulatory changes in trn underlie the evolution of clasper morphology in these species. Finally, analyses of reciprocal hemizygotes that are genetically identical, except for the species from which the functional allele of trn originates, determined that the trn allele of D. mauritiana specifies larger claspers with more bristles than the allele of D. simulans Therefore, we have identified a gene underlying evolutionary change in the size of a male genital organ, which will help to better understand not only the rapid diversification of these structures, but also the regulation and evolution of organ size more broadly.

| S-EPMC6754542 | biostudies-literature

The Genetic Basis of Rapidly Evolving Male Genital Morphology in Drosophila

2011-07-22 | GSE28663 | GEO

The Genetic Basis of Rapidly Evolving Male Genital Morphology in Drosophila.

2011-07-21 | GSE26348 | GEO

The Genetic Basis of Rapidly Evolving Male Genital Morphology in Drosophila.

Project description:We performed genome-wide expression assays comparing gene expression in the Drosophila melanogaster third larval instar genital imaginal disc between males and females. We used microarrays to compare the relative expression levels of five independent male versus female comparisons for each of two different D. melanogaster wild-type strains, Canton-S and Berlin. All microarrays were dual channel direct comparisons of late third larval instar male versus female genital imaginal discs from two Drosophila melanogaster wildtype strains, Canton S and Berlin. For each strain five independent biological samples were analyzed using a dye-swap design (i.e. male samples labeled with Cy5 in three replicates were labeled with Cy3 in the other two replicates in that experimental set).

2011-07-20 | E-GEOD-26348 | biostudies-arrayexpress

The Genetic Basis of Rapidly Evolving Male Genital Morphology in Drosophila

Project description:Deep sequencing of total RNA extracted from the genital discs of males for each of the following strains : Drosophila sechellia, Drosophila mauritiana, hybrid introgression line 3Q1(A) and hybrid introgression line Q1(A) Analysis of poly(A)+ RNA for three independent biological replicates of sequencing libraries for each of the following strains: D. sechellia w, D. mauritiana P-insertion Q1, hybrid introgression line 3Q1(A), and hybrid introgression line Q1(A). Male genital discs were obtained as described above, and total RNA was extracted using RNAqueousM-CM-^BM-BM-.-Micro Kit (Ambion). Poly(A)+ transcripts were isolated subsequently using MicroPoly(A)PuristM-CM-"M-BM-^DM-BM-" Kit (Ambion). To facilitate normalization of reads across our samples, at this stage of library construction we spiked-in small amounts of exogenous RNA from ArrayControlM-CM-"M-BM-^DM-BM-" Kit (Ambion) into each sample of poly(A)+ RNA. Paired-end sequencing was carried out by loading the samples onto four lanes (three samples per lane) of a flow cell and run on an Illumina Genome Analyzer IIx sequencer using 72 cycles per end of each paired-end read. Biological replicates of each genotype were loaded onto separate lanes.

2011-07-22 | E-GEOD-28663 | biostudies-arrayexpress

Baculum morphology predicts reproductive success of male house mice under sexual selection.

Project description:Diversity in penile morphology is characterised by extraordinary variation in the size and shape of the baculum (penis bone) found in many mammals. Although functionally enigmatic, diversity in baculum form is hypothesised to result from sexual selection. According to this hypothesis, the baculum should influence the outcome of reproductive competition among males within promiscuous mating systems. However, a test of this key prediction is currently lacking.Here we show that baculum size explains significant variation in the reproductive success of male house mice under competitive conditions. After controlling for body size and other reproductive traits, the width (but not length) of the house mouse baculum predicts both the mean number of offspring sired per litter and total number of offspring sired.By providing the first evidence linking baculum morphology to male reproductive success, our results support the hypothesis that evolutionary diversity in baculum form is driven by sexual selection.

| S-EPMC3693876 | biostudies-other

Male clasping ability, female polymorphism and sexual conflict: fine-scale elytral morphology as a sexually antagonistic adaptation in female diving beetles.

Project description:During sexual conflict, males and females are expected to evolve traits and behaviours with a sexually antagonistic function. Recently, sexually antagonistic coevolution was proposed to occur between male and female diving beetles (Dytiscidae). Male diving beetles possess numerous suction cups on their forelegs whereas females commonly have rough structures on their elytra. These rough structures have been suggested to obstruct adhesion from male suction cups during mating attempts. However, some diving beetle species are dimorphic, where one female morph has a rough elytra and the other has a smooth elytra. Here, we used biomechanics to study the adhesive performance of male suction cups on the female morphs in two diving beetle species: Dytiscus lapponicus and Graphoderus zonatus. We compared adhesion on the rough and the smooth female morphs to infer the function of the rough elytral modifications. We found that the adhesive force on the rough structures was much lower than on other surfaces. These findings support the suggestion of sexual conflict in diving beetles and a sexually antagonistic function of the rough female structures. In addition, males differed in their adhesive capacity on different female surfaces, indicating a male trade-off between adhering to smooth and rough female morphs.

| S-EPMC3730688 | biostudies-literature

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