Zoologiska institutionen: Etologi, Stockholm University, Stockholm, Sweden.
Department of Biology, University of Virginia, Charlottesville, Virginia.
J Evol Biol. 2019 Apr;32(4):302-309. doi: 10.1111/jeb.13414. Epub 2019 Feb 9.
Post-copulatory sexual selection is thought to be responsible for much of the extraordinary diversity in sperm morphology across metazoans. However, the extent to which post-copulatory selection targets sperm morphology versus sperm production is generally unknown. To address this issue, we simultaneously characterized the evolution of sperm morphology (length of the sperm head, midpiece and flagellum) and testis size (a proxy for sperm production) across 26 species of Anolis lizards, a group in which sperm competition is likely. We found that the length of the sperm midpiece has evolved 2-3 times faster than that of the sperm head or flagellum, suggesting that midpiece size may be the most important aspect of sperm morphology with respect to post-copulatory sexual selection. However, testis size has evolved faster than any aspect of sperm morphology or body size, supporting the hypothesis that post-copulatory sexual selection acts more strongly upon sperm production than upon sperm morphology. Likewise, evolutionary increases in testis size, which typically indicate increased sperm competition, are not associated with predictable changes in sperm morphology, suggesting that any effects of post-copulatory selection on sperm morphology are either weak or variable in direction across anoles. Collectively, our results suggest that sperm production is the primary target of post-copulatory sexual selection in this lineage.
交配后性选择被认为是后生动物精子形态多样性的主要原因。然而，交配后选择针对精子形态还是精子产生的程度通常是未知的。为了解决这个问题，我们同时描述了 26 种蜥蜴的精子形态（精子头部、中段和鞭毛的长度）和睾丸大小（精子产生的代表）的进化。在精子竞争可能发生的蜥蜴组中，我们发现精子中段的长度比精子头部或鞭毛进化快 2-3 倍，这表明中段大小可能是精子形态与交配后性选择有关的最重要方面。然而，睾丸大小的进化速度比任何精子形态或体型方面都快，这支持了交配后性选择对精子产生的作用强于对精子形态的作用的假说。同样，睾丸大小的进化增加，通常表明精子竞争的增加，与精子形态的可预测变化无关，这表明交配后选择对精子形态的任何影响在蜥蜴中都是微弱的或方向可变的。总的来说，我们的结果表明，在这个谱系中，精子产生是交配后性选择的主要目标。
