Both sexes exhibited convergent evolution of genital traits among populations inhabiting similar habitat types. These analyses revealed rapid and correlated divergence of female and male genitalia across evolutionarily independent population pairs exposed to divergent selection regimes. We quantified genital variation in replicated population pairs of Poecilia mexicana with ongoing ecological speciation between sulfidic (H2S‐containing) and nearby non‐sulfidic habitats. Despite widespread evidence for genital trait diversity among closely related lineages and coevolution of female and male genitalia within lineages, few studies have investigated genital evolution during the early stages of speciation. Regardless of the mechanism of sexual selection driving genital divergence, reproductive isolation may then arise as a by-product if genital incompatibilities among lineages decrease fertilization success.ĭivergence of genital traits among lineages has the potential to serve as a reproductive isolating barrier when copulation, insemination, or fertilization are inhibited by incompatibilities between female and male genitalia. Alternatively, postcopulatory sexual selection via cryptic female choice or sexual conflict-both of which may be modulated by ecological factors-can drive genital coevolution within lineages, which can incidentally lead to genital divergence between lineages (Martin and Hosken 2003 Arnqvist and Rowe 2005 Masly 2012 Evans et al. 2016), predicting that natural selection should favor the evolution of genital incompatibilities between lineages and the evolution of complementary female (lock) and male (key) genitalia within lineages when inter-lineage matings have negative fitness consequences (e.g., hybrid inferiority, physical damage Dufour 1844 Masly 2012 Langerhans et al. The lock-and-key hypothesis assumes reinforcement mechanisms (Masly 2012 Langerhans et al. Our data thereby provide novel insight into the potential for the coevolutionary divergence of male and female genital traits in a mammal. Our results reveal significant additive genetic variation in house mouse baculum morphology and cervix width, as well as evidence for genetic covariation between male and female genital measures. We applied a landmark‐based morphometrics approach to measure baculum size and shape in males and the length of the vaginal tract and width of the cervix in females. In light of this, we used a paternal half‐sibling design to explore patterns of additive genetic variation and covariation underlying baculum shape and female vaginal tract size in house mice (Mus musculus domesticus ). Much less is known of the morphology of female genitalia and its coevolution with male genitalia. Studies of house mice suggest that the shape of the baculum (penis bone) affects male reproductive fitness and experimentally imposed postmating sexual selection has been shown to drive divergence in baculum shape across generations. Male genitalia are among the most phenotypically diverse morphological traits, and sexual selection is widely accepted as being responsible for their evolutionary divergence. Our subsequent finding that physically interacting female genital traits exhibit corresponding levels of genetic (co)variation reveals the potential intersexual coevolutionary dynamics of male and female genitalia, thereby fulfilling a fundamental assumption underlying CFC and SC theory. Our results from a paternal half-sibling breeding design reveal substantial levels of additive genetic variation underlying male genital size and morphology-two traits known to predict mating success during non-consensual matings. Here, we provide evidence for this prediction in the guppy (Poecilia reticulata), a polyandrous livebearing fish in which males transfer sperm internally to females via consensual and forced matings. A critical but rarely explored assumption underlying both processes is that male and female reproductive traits coevolve, either via the classic Fisherian model of preference-trait coevolution (CFC) or through sexually antagonistic selection (SC). On the one hand, females may exploit postcopulatory mechanisms of selection to favour males with preferred genital traits (cryptic female choice CFC), while on the other hand females may evolve structures or behaviours that mitigate the direct costs imposed by male genitalia (sexual conflict SC). Among the evolutionary mechanisms proposed to account for this diversity, two processes in particular have generated considerable interest. The spectacular variability that typically characterizes male genital traits has largely been attributed to the role of sexual selection.
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