Pitnick Scott, Miller Gary T, Schneider Karin, Markow Therese A
Department of Biology, Syracuse University, 108 College Place, Syracuse, NY 13244-1270, USA.
Proc Biol Sci. 2003 Jul 22;270(1523):1507-12. doi: 10.1098/rspb.2003.2382.
Interspecific studies indicate that sperm morphology and other ejaculatory traits diverge more rapidly than other types of character in Drosophila and other taxa. This pattern has largely been attributed to postcopulatory sexual selection involving interaction between the sexes. Such divergence has been suggested to lead rapidly to reproductive isolation among populations and thus to be an 'engine of speciation.' Here, we test two critical predictions of this hypothesis: (i) there is significant variation in reproductive traits among incipient species; and (ii) divergence in interacting sex-specific traits exhibits a coevolutionary pattern among populations within a species, by examining geographical variation in Drosophila mojavensis, a species in the early stages of speciation. Significant among-population variation was identified in sperm length and female sperm-storage organ length, and a strong pattern of correlated evolution between these interacting traits was observed. In addition, crosses among populations revealed coevolution of male and female contributions to egg size. Support for these two important predictions confirms that coevolving internal characters that mediate successful reproduction may play an important part in speciation. The next step is to determine exactly what that role is.
种间研究表明，在果蝇和其他分类群中，精子形态及其他射精特征比其他类型的性状分化得更快。这种模式很大程度上归因于涉及两性相互作用的交配后性选择。有人认为这种分化会迅速导致种群间的生殖隔离，因此是“物种形成的引擎”。在此，我们通过研究处于物种形成早期阶段的莫哈韦果蝇的地理变异，来检验这一假说的两个关键预测：（i）初始物种间生殖性状存在显著差异；（ii）相互作用的性别特异性性状的分化在一个物种内的种群间呈现协同进化模式。我们在精子长度和雌性精子储存器官长度方面发现了显著的种群间差异，并观察到这些相互作用性状之间存在强烈的协同进化模式。此外，种群间的杂交揭示了雄性和雌性对卵大小的贡献的协同进化。对这两个重要预测的支持证实，介导成功繁殖的协同进化内部性状可能在物种形成中起重要作用。下一步是确切确定这个作用是什么。
