Data from: Postmating sexual selection and the enigmatic jawed genitalia of Callosobruchus subinnotatus

Insect genitalia exhibit rapid divergent evolution. Truly extraordinary structures have evolved in some groups, presumably as a result of post-mating sexual selection. To increase our understanding of this phenomenon, we studied the function of one such structure. The male genitalia of Callosobruchus subinnotatus (Coleoptera: Bruchinae) contain a pair of jaw-like structures with unknown function. Here, we used phenotypic engineering to ablate the teeth on these jaws. We then experimentally assessed the effects of ablation of the genital jaws on mating duration, ejaculate weight, male fertilization success and female fecundity, using a double-mating experimental design. We predicted that copulatory wounding in females should be positively related to male fertilization success. However, we found no significant correlation between genital tract scarring in females and male fertilization success. Male fertilization success was, however, positively related to the amount of ejaculate transferred by males and negatively related to female ejaculate dumping. Ablation of male genital jaws did not affect male relative fertilization success but resulted in a reduction in female egg production. Our results suggest that postmating sexual selection in males indeed favors these genital jaws, but not primarily through an elevated relative success in sperm competition but by increasing female egg production.

昆虫生殖器呈现出快速趋异演化。部分类群演化出了极为独特的生殖器结构，这一现象推测是交配后性选择（post-mating sexual selection）作用的结果。为加深对该现象的理解，我们针对一类此类结构的功能展开了研究。四纹豆象（Callosobruchus subinnotatus，鞘翅目：豆象亚科）的雄性生殖器具有一对功能未知的颚状结构。本研究通过表型工程（phenotypic engineering）技术切除了该颚状结构上的齿突，并采用双交配实验设计（double-mating experimental design），评估了生殖器颚状结构切除对交配时长、射精量、雄性受精成功率以及雌性繁殖力的影响。我们曾预测雌性的交配创伤程度与雄性受精成功率呈正相关，但实验结果显示，雌性生殖器的瘢痕形成情况与雄性受精成功率之间并无显著相关性。不过，雄性受精成功率与雄性转移的射精量呈正相关，与雌性的精液倾倒行为呈负相关。雄性生殖器颚状结构的切除并未影响雄性的相对受精成功率，但却导致雌性产卵量下降。本研究结果表明，雄性的交配后性选择确实对这类生殖器颚状结构存在正向选择，但这一选择并非主要通过提升精子竞争（sperm competition）中的相对成功率实现，而是通过提高雌性的产卵量来达成。