Data from: How the length of genital parts affects copulation performance in a carabid beetle: implications for correlated genital evolution between the sexes

To identify factors leading to the correlated evolution of exaggerated male and female genitalia, we studied the effects of the variable dimensions of corresponding functional genital parts (male copulatory piece and female vaginal appendix) on copulatory performance in the polygamous carabid beetle Carabus (Ohomopterus) maiyasanus. We used mating pairs of individuals from two populations to increase the variances in genital dimensions and determined the copulation performance (insemination and spermatophore replacement, and copulation time) in single- and double-mating situations. In single mating, insemination success was not affected by genital dimensions, although the copulation time was significantly shorter when the male aedeagus was longer. In the double-mating experiment, insemination and replacement of spermatophores by the second male succeeded more frequently when the copulatory piece was shorter and the vaginal appendix was longer, and when the difference between the length of the copulatory piece and the vaginal appendix was smaller. Thus, a matching of the corresponding genital parts between the sexes increases the male's reproductive success in sperm competition, but elongation of the copulatory piece cannot be explained simply by the improvement in male reproductive success. We discuss possible factors for the elongation of genital parts in terms of sexual conflict and reproductive interference through interspecific copulation.

为明确驱动雌雄夸张生殖器协同演化的潜在因素，我们以多配制步甲科甲虫大文字步行虫（Carabus (Ohomopterus) maiyasanus）为研究对象，探究对应功能性生殖器结构（雄性交配片（copulatory piece）与雌性阴道附件（vaginal appendix））的可变尺寸对交配表现的影响。我们采用两个种群的个体构建交配配对，以扩大生殖器尺寸的变异范围，并分别测定单交配与双交配情境下的交配表现，包括授精情况、精荚替换行为及交配时长。
在单交配情境中，尽管雄性阳茎（aedeagus）更长的个体交配时长显著更短，但授精成功率并未受生殖器尺寸的影响。在双交配实验中，当雄性交配片更短、雌性阴道附件更长，且二者长度差值较小时，首次授精与第二雄性的精荚替换行为成功率均显著更高。
由此可见，雌雄对应生殖器结构的匹配度提升可增强雄性在精子竞争中的繁殖成功率，但雄性交配片的伸长演化无法仅通过雄性繁殖成功率的提升来解释。我们将从性冲突以及种间交配引发的生殖干扰两个维度，探讨生殖器结构伸长演化的潜在驱动因素。