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.

中文翻译：

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杂种的交配和持久生殖隔离

建立限制种群之间基因流动的机制可以驱动新物种的出现。一个主要的挑战是如何使物种交配在物种形成中的理论和经验重要性与失败的可能性相协调。剑尾鱼具有杂交和脆弱的合子前分离机制的进化历史。在1990年代，两种剑尾鱼之间的杂交很可能是由于污染介导的交配交配的破坏而引起的。在这里，我们使用全基因组测序来追踪过去十年中一个杂种种群的异常遗传模式。到2003年，该种群中的杂种形成了独立的遗传簇，并通过强大的祖先-交配交配，在25代中保持了近乎完美的隔离。但是，我们还发现分类交配是塑料的，强度会随时间变化，并在受控条件下消失。另外，附近的人群没有显示出交配的迹象。因此，我们的发现表明，杂种交配可能构成基因流的间歇性和不可预测的障碍，但是其强度的差异可能会对杂种种群的进化产生重大影响。了解生殖隔离在不同人群之间以及随着时间的变化如何，对于了解物种形成和杂交以及它们对干扰的依赖性至关重要。但是强度上的差异可能会对杂种种群的进化产生重大影响。了解生殖隔离在不同人群之间以及随着时间的变化如何，对于了解物种形成和杂交以及它们对干扰的依赖性至关重要。但是强度上的差异可能会对杂种种群的进化产生重大影响。了解生殖隔离在不同人群之间以及随着时间的变化如何，对于了解物种形成和杂交以及它们对干扰的依赖性至关重要。