Post-copulatory sexual selection is associated with sperm aggregate quality in Peromyscus mice

In some species, sperm form coordinated groups that are hypothesized to improve their swimming performance in competitive contexts or to navigate through the viscous fluids of the female reproductive tract. Here we investigate sperm aggregation across closely-related species of Peromyscus mice that naturally vary by mating system to test the predictions that sperm aggregates (1) are faster than solitary sperm in species that females mate multiply to aid cells in sperm competition, and (2) outperform solitary sperm cells in viscous environments. We find significant variation in the size of sperm aggregates, which negatively associates with relative testis mass, a proxy for sperm competition risk, suggesting that post-copulatory sexual selection has a stabilizing effect on sperm group size. Moreover, our results show that sperm aggregates are faster than solitary sperm in some, but not all, species, and this can vary by fluid viscosity. Of the two species that produce the largest and most...部分物种的精子会形成协同聚集的群体，学界推测此类聚集可提升精子在竞争环境中的游动能力，或帮助其穿透雌性生殖道的粘性体液。本研究针对交配系统存在自然差异的近缘鹿鼠属（Peromyscus）小鼠物种开展精子聚集相关研究，以验证两项假说：其一，在雌性存在多次交配行为的物种中，精子聚集体的游动速度快于单个精子，以帮助精子在精子竞争中获胜；其二，在粘性环境中，精子聚集体的表现优于单个精子。研究发现精子聚集体的大小存在显著差异，且该差异与相对睾丸质量呈负相关——相对睾丸质量可作为精子竞争风险的替代指标，这表明交配后性选择对精子群体大小具有稳定选择作用。此外，本研究结果显示，在部分而非全部物种中，精子聚集体的游动速度快于单个精子，且该差异会随流体粘度的变化而改变。在两类可形成最大且最……