Data from: Experimental reduction of intromittent organ length reduces male reproductive success in a bug

It is now clear in many species that male and female genital evolution has been shaped by sexual selection. However, it has historically been difficult to confirm correlations between morphology and fitness, as genital traits are complex and manipulation tends to impair function significantly. In this study, we investigate the functional morphology of the elongate male intromittent organ (or processus) of the seed bug Lygaeus simulans, in two ways. We first use micro-computed tomography (micro-CT) and flash-freezing to reconstruct in high resolution the interaction between the male intromittent organ and the female internal reproductive anatomy during mating. We successfully trace the path of the male processus inside the female reproductive tract. We then confirm that male processus length influences sperm transfer by experimental ablation and show that males with shortened processi have significantly reduced post-copulatory reproductive success. Importantly, male insemination function is not affected by this manipulation per se. We thus present rare, direct experimental evidence that an internal genital trait functions to increase reproductive success and show that, with appropriate staining, micro-CT is an excellent tool for investigating the functional morphology of insect genitalia during copulation.

目前已有明确证据表明，诸多物种的雌雄生殖器演化均受性选择（sexual selection）塑造。然而长期以来，由于生殖器性状结构复杂，且对其进行操作往往会显著损伤其功能，学界难以确证生殖器形态与适合度（fitness）之间的相关性。本研究以模拟长蝽（Lygaeus simulans）的雄性细长插入器官（或称突起，processus）的功能形态学为研究对象，通过两种方式展开探究：其一，我们借助显微计算机断层扫描（micro-computed tomography，简称micro-CT）与快速冷冻技术，以高分辨率重构交配过程中雄性插入器官与雌性内生殖器官的相互作用模式，并成功追踪到雄性突起在雌性生殖道内的行进路径；其二，我们通过实验切除法证实，雄性突起的长度会影响精子传递——突起被缩短的雄性，其交配后繁殖成功率显著降低。值得注意的是，该操作本身并不会对雄性的授精功能造成影响。因此，本研究提供了极为罕见的直接实验证据，证明内部生殖器性状可提升繁殖成功率；同时证实，在适配恰当染色流程的前提下，micro-CT是探究昆虫交配过程中生殖器功能形态学的优质工具。