Data from: Evolutionary change in testes tissue competition among experimental populations of house mice

Theory assumes that postcopulatory sexual selection favours increased investment in testes size because greater numbers of sperm within the ejaculate increase the chance of success in sperm competition, and larger testes are able to produce more sperm. However, changes in the organization of the testes tissue may also affect sperm production rates. Indeed, recent comparative analyses suggest that sperm competition selects for greater proportions of sperm-producing tissue within the testes. Here, we explicitly test this hypothesis using the powerful technique of experimental evolution. We allowed house mice (Mus domesticus) to evolve via monogamy or polygamy in six replicate populations across 24 generations. We then used histology and image analysis to quantify the proportion of sperm-producing tissue (seminiferous tubules) within the testes of males. Our results show that males that had evolved with sperm competition had testes with a higher proportion of seminiferous tubules compared with males that had evolved under monogamy. Previously, it had been shown that males from the polygamous populations produced greater numbers of sperm in the absence of changes in testes size. We thus provide evidence that sperm competition selects for an increase in the density of sperm-producing tissue, and consequently increased testes efficiency.

现有理论认为，交配后性选择会倾向于促使生物体增大睾丸体积——因为射精中精子数量越多，在精子竞争中获胜的概率就越高，而更大的睾丸能够产生更多精子。不过，睾丸组织的结构变化同样可能影响精子生成速率。事实上，近期的比较分析研究表明，精子竞争会促使睾丸内精子生成组织的占比提升。本研究借助实验进化这一强大研究手段，对该假说进行了直接检验。我们让小家鼠（Mus domesticus）在6个重复种群中分别以单配制或多配制的方式繁衍，历经24代演化。随后我们通过组织学和图像分析技术，对雄性个体睾丸内精子生成组织（生精小管，seminiferous tubules）的占比进行了定量检测。研究结果显示，经历过精子竞争的演化种群的雄性个体，其睾丸内的生精小管占比显著高于单配制演化种群的雄性。此前已有研究证实，多配制种群的雄性个体在睾丸体积未发生改变的前提下，能够产生更多的精子。因此，本研究为精子竞争会促使精子生成组织密度提升、进而提升睾丸生精效率这一结论提供了实证依据。