Female adaptations to sense or oppose features of male genitalia can be subtle, requiring careful study. Female genitalia also tend to be softer than male genitalia and thus their morphology may be more difficult to describe, and can more easily be distorted on dissection and preservation. Male genitalia are generally kept inside of the body cavity, but are everted before, or during copulation, so their functional morphology can be more easily studied than the internal genitalia of females. However, studying female genitalia is undeniably challenging. Female genitalia are not studied as often as male genitalia, perhaps because of a male-biased view of evolutionary processes by researchers ( Ah-King et al. In contrast, female genitalia have typically been found not to be as interspecifically variable as male genitalia in several studies that specifically examined and described them ( Eberhard 1985, 2010a, b). Male genitalia are among the most variable structures in nature ( Eberhard 1985). Shape correspondence is often taken as evidence of coevolution, although it is not as conclusive as other approaches. The evidence provided by the studies can be comparative among species or among populations, experimental evolution, cross-species matings, full-sibling (sib)/half-sib matings, shape, and length correspondence. The likely mechanism is that suggested by the authors, and it includes sexually antagonistic coevolution (SAC), natural selection, sexual selection, female choice, or none specified. Shape correspondence and comparison with close relatives
Vestibular colliculus (fleshy fold) that partially obstructs the entrance to the vagina Morphological observation and two-species comparison Rodents: Cape dune mole: Bathyergus suillus Insectivores: Short-tailed shrew: Blarina brevicaudaįiliform penis (up to 70% of the male’s body length) PLR Brennan, K Zyscowski, and RO Prum, unpubl. Pope 1941 Böhme and Ziegler 2009 King et al. Signa: Sclerotized structure to break spermatophores Spermathecal ducts length, base of the ductįemale competition (role reversal), coevolution SAC
yakubaĬomparative among species and morphological Vaginal appendix (pocket attached to the vaginal apophysis)ĭiptera: Drosophila santomea and D. Robertson and Paterson 1982 McPeek et al. Natural selection against fluid loss, lock and key, and sexual selectionįunctional morphology, comparative among species Two-species comparison, shape correspondence Mechanical incompatibility resulting from Intersexual selectionĪccesory lobe of the vulva and distal projection Therefore, attention to vertebrates in any of these areas is badly needed. Knowledge of the ecology and behavior of the studied species combined with functional morphology, quantitative morphological tools, experimental manipulation, and experimental evolution have been provided in the best-studied species, all of which are invertebrates. A combination of different approaches is required to continue to advance our understanding of genital coevolution. Although some good examples exist in support of each of these mechanisms, more data on quantitative female genital variation and studies of functional morphology during copulation are needed to understand more general patterns. Genital coevolution is explicitly predicted by at least three mechanisms of genital evolution: lock and key to prevent hybridization, female choice, and sexual conflict. Natural selection on genital morphology will result in size coevolution to allow for copulation to be mechanically possible, even as other features of genitalia may reflect the action of other mechanisms of selection. Here we review the diverse mechanisms of genital coevolution that include natural selection, female mate choice, male–male competition, and how their interactions generate sexual conflict that can lead to sexually antagonistic coevolution. Genital coevolution between the sexes is expected to be common because of the direct interaction between male and female genitalia during copulation.
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