Postcopulatory sexual selection is associated with accelerated evolution of sperm morphology

Rapid diversification of sexual traits is frequently attributed to sexual selection, though explicit tests of this hypothesis remain limited. Spermatozoa exhibit remarkable variability in size and shape, and studies report a correlation between sperm morphology (sperm length and shape) and sperm competition risk or female reproductive tract morphology. However, whether postcopulatory processes (e.g. sperm competition and cryptic female choice) influence the speed of evolutionary diversification in sperm form is unknown. Using passerine birds, we quantified evolutionary rates of sperm length divergence among lineages (i.e. species pairs) and determined whether these rates varied with the level of sperm competition (estimated as relative testes mass). We found that relative testes mass was significantly and positively associated with more rapid phenotypic divergence in sperm midpiece and flagellum lengths, as well as total sperm length. In contrast, there was no association between relati...

性特征的快速多样化通常被归因于性选择，但针对该假说的直接检验仍较为有限。精子在大小与形态上表现出显著变异，已有研究表明精子形态（包括精子长度与外形）与精子竞争（sperm competition）风险或雌性生殖道形态之间存在相关性。然而，交配后过程（如精子竞争与隐性雌性选择（cryptic female choice））是否会影响精子形态的进化多样化速率，目前仍不明确。本研究以雀形目鸟类（passerine birds）为研究对象，量化了不同谱系（即物种对）间精子长度分化的进化速率，并检验了这些速率是否随精子竞争水平（以相对睾丸质量（relative testes mass）估算）发生变化。研究结果显示，相对睾丸质量与精子中段（sperm midpiece）、鞭毛（flagellum）长度以及总精子长度的更快表型分化呈显著正相关。与之相反，相对