Data from: Evolution of male and female genitalia following release from sexual selection

Despite the key functions of the genitalia in sexual interactions and fertilization, the role of sexual selection and conflict in shaping genital traits remains poorly understood. Seed beetle (Callosobruchus maculatus) males possess spines on the intromittent organ, and females possess a thickened reproductive tract wall that also bears spines. We investigated the role of sexual selection and conflict by imposing monogamous mating on eight replicate populations of this naturally polygamous insect, while maintaining eight other populations under polygamy. To establish whether responses to mating system manipulation were robust to ecological context, we simultaneously manipulated life history selection (early/late reproduction). Over 18-21 generations, male genital spines evolved relatively reduced length in large males (i.e., shallower static allometry) in monogamous populations. Two non-intromittent male genital appendages also evolved in response to the interaction of mating system and ecology. In contrast, no detectable evolution occurred in female genitalia, consistent with the expectation of a delayed response in defensive traits. Our results support a sexually antagonistic role for the male genital spines, and demonstrate the evolution of static allometry in response to variation in sexual selection opportunity. We argue that further advances in the study of genital coevolution will require a much more detailed understanding of the functions of male and female genital traits.尽管生殖器在性交互与受精过程中发挥着核心功能，但性选择与性冲突在塑造生殖器性状演化中的作用仍未得到充分阐释。豆象（Callosobruchus maculatus）雄性的交尾插入器官上生有棘刺，而雌性的生殖道壁不仅增厚，同样带有棘刺。为探究性选择与性冲突的作用，我们将该天然多配偶昆虫的8个重复种群实施单配偶交配处理，同时将另外8个种群维持于多配偶交配体系。为明确交配体系操控的响应是否在不同生态背景下均具有稳健性，我们同时对生活史选择（早/晚繁殖）进行了操控。历经18至21代演化后，单配偶种群中的雄性个体，其生殖器棘刺在体型较大的雄性中演化出相对更短的长度——即静态异速生长（static allometry）变缓。另外两种非交尾插入式的雄性生殖器附肢，也随交配体系与生态因子的交互作用发生了演化。与之形成鲜明对比的是，雌性生殖器未出现可检测到的演化，这与防御性状响应存在延迟的理论预期相符。我们的研究结果为雄性生殖器棘刺的性拮抗作用提供了实证支持，并证实静态异速生长可随性选择机会的变化发生演化。我们主张，若要在生殖器协同进化（genital coevolution）研究领域取得进一步突破，需对雌雄两性生殖器性状的功能开展更为细致深入的解析。