Dean Matthew D, Nachman Michael W
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USA.
Evolution. 2009 Jan;63(1):20-8. doi: 10.1111/j.1558-5646.2008.00499.x. Epub 2008 Aug 26.
Barriers to gene flow can arise at any stage in the reproductive sequence. Most studies of reproductive isolation focus on premating or postzygotic phenotypes, leaving the importance of differences in fertilization rate overlooked. Two closely related species of house mice, Mus domesticus and M. musculus, form a narrow hybrid zone in Europe, suggesting that one or more isolating factors operate in the face of ongoing gene flow. Here, we test for differences in fertilization rate using laboratory matings as well as in vitro sperm competition assays. In noncompetitive matings, we show that fertilization occurs significantly faster in conspecific versus heterospecific matings and that this difference arises after mating and before zygotes form. To further explore the mechanisms underlying this conspecific advantage, we used competitive in vitro assays to isolate gamete interactions. Surprisingly, we discovered that M. musculus sperm consistently outcompeted M. domesticus sperm regardless of which species donated ova. These results suggest that in vivo fertilization rate is mediated by interactions between sperm, the internal female environment, and/or contributions from male seminal fluid. We discuss the implications of faster conspecific fertilization in terms of reproductive isolation among these two naturally hybridizing species.
基因流动的障碍可能在生殖序列的任何阶段出现。大多数关于生殖隔离的研究都集中在交配前或合子后的表型上，而受精率差异的重要性则被忽视了。家鼠的两个近缘物种，即小家鼠（Mus domesticus）和小鼠（M. musculus），在欧洲形成了一个狭窄的杂交带，这表明在持续的基因流动面前，存在一个或多个隔离因素。在这里，我们通过实验室交配以及体外精子竞争试验来检测受精率的差异。在非竞争性交配中，我们发现同种交配与异种交配相比，受精发生得明显更快，而且这种差异出现在交配后和受精卵形成之前。为了进一步探究这种同种优势背后的机制，我们使用竞争性体外试验来分离配子间的相互作用。令人惊讶的是，我们发现无论哪个物种提供卵子，小鼠的精子始终比小家鼠的精子更具竞争力。这些结果表明，体内受精率是由精子、雌性内部环境和/或雄性精液的贡献之间的相互作用介导的。我们讨论了在这两个自然杂交物种中，同种受精更快对生殖隔离的影响。
