Department of Animal and Plant Sciences, University of Sheffield, , Western Bank, Sheffield S10 2TN, UK.
Proc Biol Sci. 2012 Oct 22;279(1745):4174-82. doi: 10.1098/rspb.2012.1398. Epub 2012 Aug 15.
The striking diversity of sperm shape across the animal kingdom is still poorly understood. Postcopulatory sexual selection is an important factor driving the evolution of sperm size and shape. Interestingly, morphometric sperm traits, such as the length of the head, midpiece and flagellum, exhibit a strong positive phenotypic correlation across species. Here we used recently developed comparative methods to investigate how such phenotypic correlations between morphometric sperm traits may evolve. We compare allometric relationships and evolutionary trajectories of three morphometric sperm traits (length of head, midpiece and flagellum) in passerine birds. We show that these traits exhibit strong phenotypic correlations but that allometry varies across families. In addition, the evolutionary trajectories of the midpiece and flagellum are similar while the trajectory for head length differs. We discuss our findings in the light of three scenarios accounting for correlated trait evolution: (i) genetic correlation; (ii) concerted response to selection acting simultaneously on different traits; and (iii) phenotypic correlation between traits driven by mechanistic constraints owing to selection on sperm performance. Our results suggest that concerted response to selection is the most likely explanation for the phenotypic correlation between morphometric sperm traits.
动物界中精子形状的惊人多样性仍然知之甚少。交配后性选择是推动精子大小和形状进化的重要因素。有趣的是，形态学精子特征，如头部、中段和鞭毛的长度，在物种间表现出强烈的正表型相关性。在这里，我们使用最近开发的比较方法来研究形态学精子特征之间的这种表型相关性如何进化。我们比较了雀形目鸟类中三种形态学精子特征（头部、中段和鞭毛的长度）的比例关系和进化轨迹。我们表明，这些特征表现出强烈的表型相关性，但比例关系因科而异。此外，中段和鞭毛的进化轨迹相似，而头部长度的轨迹则不同。我们根据三种解释相关特征进化的情景讨论了我们的发现：（i）遗传相关性；（ii）同时对不同特征起作用的选择的协同反应；（iii）由于对精子性能的选择导致的机制约束下的特征之间的表型相关性。我们的结果表明，协同反应选择是形态学精子特征之间表型相关性的最可能解释。
