Laboratoire Ecologie, Systématique et Evolution, Université Paris Sud, 91405 Orsay, France.
Evolution. 2012 Jun;66(6):1917-30. doi: 10.1111/j.1558-5646.2011.01563.x. Epub 2012 Mar 3.
Closely related species coexisting in sympatry provide critical insight into the mechanisms underlying speciation and the maintenance of genetic divergence. Selfing may promote reproductive isolation by facilitating local adaptation, causing reduced hybrid fitness in parental environments. Here, we propose a novel mechanism by which selfing can further impair interspecific gene flow: selfing may act to ensure that nonhybrid progeny systematically co-occur whenever hybrid genotypes are produced. Under a competition arena, the fitness differentials between nonhybrid and hybrid progeny are then magnified, preventing development of interspecific hybrids. We investigate whether this "sibling competition arena" can explain the coexistence in sympatry of closely related species of the plant fungal pathogens (Microbotryum) causing anther-smut disease. The probabilities of intrapromycelial mating (automixis), outcrossing, and sibling competition were manipulated in artificial inoculations to evaluate their contribution to reproductive isolation. We report that both intrapromycelial selfing and sibling competition significantly reduced rates of hybrid infection beyond that expected based solely upon selfing rates and noncompetitive fitness differentials between hybrid and nonhybrid progeny. Our results thus suggest that selfing and a sibling competition arena can combine to constitute a barrier to gene flow and diminish selection for additional barriers to gene flow in sympatry.
在同域共存的密切相关的物种中，它们共同为物种形成和遗传分化的维持机制提供了重要的见解。自交可以通过促进局部适应来促进生殖隔离，导致亲代环境中杂种的适应性降低。在这里，我们提出了一个自交可以进一步损害种间基因流动的新机制：自交可以确保每当产生杂种基因型时，非杂种后代系统地共同出现。在竞争场中，非杂种和杂种后代之间的适应性差异就会放大，从而阻止种间杂种的产生。我们研究了这种“兄弟姐妹竞争场”是否可以解释引起花药黑粉病的植物真菌病原体（Microbotryum）的密切相关物种在同域共存的现象。在人工接种中操纵了胞内交配（自体受精）、异交和兄弟姐妹竞争的概率，以评估它们对生殖隔离的贡献。我们报告说，胞内自交和兄弟姐妹竞争都显著降低了杂种感染的速度，这超过了仅基于自交率和杂种与非杂种后代之间非竞争适应性差异的预期。因此，我们的研究结果表明，自交和兄弟姐妹竞争场可以结合起来形成对基因流动的障碍，并减少对同域中额外基因流动障碍的选择。
