Harvard Society of Fellows, Harvard University, Cambridge, MA 02138;
Department of Biological Sciences, Columbia University, New York, NY 10027.
Proc Natl Acad Sci U S A. 2017 Oct 10;114(41):10936-10941. doi: 10.1073/pnas.1711238114. Epub 2017 Sep 25.
The emergence of new species is driven by the establishment of mechanisms that limit gene flow between populations. A major challenge is reconciling the theoretical and empirical importance of assortative mating in speciation with the ease with which it can fail. Swordtail fish have an evolutionary history of hybridization and fragile prezygotic isolating mechanisms. Hybridization between two swordtail species likely arose via pollution-mediated breakdown of assortative mating in the 1990s. Here we track unusual genetic patterns in one hybrid population over the past decade using whole-genome sequencing. Hybrids in this population formed separate genetic clusters by 2003, and maintained near-perfect isolation over 25 generations through strong ancestry-assortative mating. However, we also find that assortative mating was plastic, varying in strength over time and disappearing under manipulated conditions. In addition, a nearby population did not show evidence of assortative mating. Thus, our findings suggest that assortative mating may constitute an intermittent and unpredictable barrier to gene flow, but that variation in its strength can have a major effect on how hybrid populations evolve. Understanding how reproductive isolation varies across populations and through time is critical to understanding speciation and hybridization, as well as their dependence on disturbance.
新物种的出现是由限制种群间基因流动的机制所驱动的。一个主要的挑战是调和在物种形成中选择性交配的理论和经验重要性与它容易失败之间的关系。剑尾鱼的进化历史经历了杂交和脆弱的合子前隔离机制。20 世纪 90 年代，由于污染导致的选择性交配破裂，两种剑尾鱼之间可能发生了杂交。在这里，我们使用全基因组测序技术，在过去十年中追踪了一个混合种群中的异常遗传模式。到 2003 年，该种群中的杂种形成了单独的遗传簇，并通过强烈的祖先选择性交配，在 25 代以上保持了近乎完美的隔离。然而，我们也发现选择性交配具有可塑性，其强度随时间变化，并在人为条件下消失。此外，附近的一个种群没有表现出选择性交配的证据。因此，我们的研究结果表明，选择性交配可能构成基因流动的间歇性和不可预测的障碍，但它的强度变化可能对杂种种群的进化产生重大影响。了解生殖隔离在不同种群和不同时间的变化对于理解物种形成和杂交以及它们对干扰的依赖关系至关重要。
