Testis tissue data

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 testicular efficiency.

数据来源：家鼠实验种群中睾丸组织竞争的演化变化

理论假定，交配后性选择会倾向于提升睾丸体积的投入：射精内精子数量越多，其在精子竞争中的获胜概率就越高，且更大的睾丸可生成更多精子。然而，睾丸组织的结构变化同样可能影响精子生成速率。实际上，近期的比较分析表明，精子竞争会选择使睾丸内精子生成组织的占比提升。

本研究借助实验演化这一强有力的技术手段，对该假说进行了直接检验。我们让家鼠（Mus domesticus）在6个重复种群中分别以单配偶制或多配偶制模式演化，持续24代。随后通过组织学方法与图像分析，量化了雄性个体睾丸内精子生成组织（生精小管，seminiferous tubules）的占比。

研究结果显示，经历过精子竞争的雄性个体，其睾丸内的生精小管占比高于单配偶制下演化的雄性个体。此前已有研究表明，多配偶制种群的雄性个体可产生更多精子，且睾丸体积未发生变化。因此，本研究提供了证据证实：精子竞争会选择提升生精组织的密度，进而提高睾丸的生精效率。