Kleven Oddmund, Laskemoen Terje, Fossøy Frode, Robertson Raleigh J, Lifjeld Jan T
Natural History Museum, Department of Zoology, University of Oslo, PO Box 1172 Blindern, NO-0318 Oslo, Norway.
Evolution. 2008 Feb;62(2):494-9. doi: 10.1111/j.1558-5646.2007.00287.x. Epub 2007 Dec 7.
Spermatozoa are among the most diversified cells in the animal kingdom, but the underlying evolutionary forces affecting intraspecific variation in sperm morphology are poorly understood. It has been hypothesized that sperm competition is a potent selection pressure on sperm variation within species. Here, we examine intraspecific variation in total sperm length of 22 wild passerine bird species (21 genera, 11 families) in relation to the risk of sperm competition, as expressed by the frequency of extrapair paternity and relative testis size. We demonstrate, by using phylogenetic comparative methods, that between-male variation in sperm length within species is closely and negatively linked to the risk of sperm competition. This relationship was even stronger when only considering species in which data on sperm length and extrapair paternity originated from the same populations. Intramale variation in sperm length within species was also negatively, although nonsignificantly, related to sperm competition risk. Our findings suggest that postcopulatory sexual selection is a powerful evolutionary force reducing the intraspecific phenotypic variation in sperm-size traits, potentially driving the diversification of sperm morphology across populations and species.
精子是动物王国中最多样化的细胞之一，但影响精子形态种内变异的潜在进化力量却鲜为人知。有假说认为，精子竞争是物种内精子变异的强大选择压力。在此，我们研究了22种野生雀形目鸟类（21属，11科）的精子总长度的种内变异与精子竞争风险之间的关系，精子竞争风险通过婚外父权频率和相对睾丸大小来表示。我们运用系统发育比较方法证明，物种内雄性间精子长度的变异与精子竞争风险密切且呈负相关。当仅考虑精子长度和婚外父权数据来自相同种群的物种时，这种关系更为强烈。物种内雄性个体精子长度的变异与精子竞争风险也呈负相关，尽管不显著。我们的研究结果表明，交配后的性选择是一种强大的进化力量，可减少精子大小性状的种内表型变异，有可能推动精子形态在种群和物种间的多样化。
