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 ...为揭示驱动雌雄夸张生殖器协同演化的关键因子，本研究以多配性步甲科甲虫Maiyasan步行甲（Carabus (Ohomopterus) maiyasanus）为实验材料，探究对应功能性生殖器组分——雄性交配突（copulatory piece）与雌性阴道附器（vaginal appendix）——的可变尺寸对交配表现的影响。我们选取两个种群的个体组建交配对以增大生殖器尺寸的变异度，并测定了单次交配与两次交配情境下的交配表现，包括授精成功率、精荚（spermatophore）替换情况以及交配时长。在单次交配实验中，尽管雄性阳茎（aedeagus）更长时交配时长显著缩短，但授精成功率并未受到生殖器尺寸的影响。在两次交配实验中，当雄性交配突更短、雌性阴道附器更长，且二者长度差异……时，第二次雄性的授精与精荚替换成功率显著更高。