Institut für Populationsgenetik, Vetmeduni Vienna, Vienna, Austria.
Evolution. 2012 Jan;66(1):229-39. doi: 10.1111/j.1558-5646.2011.01423.x. Epub 2011 Aug 28.
Hybridization is common in nature, even between "good" species. This observation poses the question of why reinforcement is not always successful in leading to the evolution of complete reproductive isolation. To study this question, we developed a new "quasi-linkage disequilibrium" (QLD) approximation to obtain the first analytic results for the evolution of modifiers that increase mate discrimination against hybrids and heterospecifics. When such modifiers have small effects, they evolve more readily under a one-allele than a two-allele mechanism (sensu Felsenstein 1981). The strength of selection on the modifier decreases as hybrids decrease in frequency, and so further reinforcement may not occur once hybridization is sufficiently rare. The outcome is qualitatively different when modifiers have large effects, however, for example, when a single mutation can cause complete reproductive isolation. In this case, modifiers in a two-allele mechanism can be selected as or more strongly than those in a one-allele mechanism. Furthermore, they can spread under quite general conditions. Thus, whether complete closure of genetic introgression by reinforcement occurs may depend on the size of effects that mutations have on the sensory systems used in mate choice.
杂交在自然界中很常见，即使在“良好”的物种之间也是如此。这一观察结果提出了一个问题，即为什么强化并不总是成功地导致完全生殖隔离的进化。为了研究这个问题，我们开发了一种新的“准连锁不平衡”（QLD）近似方法，以获得第一个关于增加对杂种和异质个体的配偶歧视的修饰因子进化的分析结果。当这些修饰因子的影响较小时，它们在单等位基因机制下比在双等位基因机制下更容易进化（Felsenstein 1981 年）。随着杂种频率的降低，对修饰因子的选择强度也会降低，因此一旦杂交变得足够罕见，进一步的强化可能不会发生。然而，当修饰因子的影响较大时，结果就会有所不同，例如，当单个突变可以导致完全生殖隔离时。在这种情况下，双等位基因机制中的修饰因子可以被选择，或者比单等位基因机制中的修饰因子更强烈地被选择。此外，它们可以在相当普遍的条件下传播。因此，强化是否会导致遗传渗入的完全关闭，可能取决于突变对用于配偶选择的感觉系统的影响大小。
