An increasing volume of empirical studies demonstrated that hybridization between distant lineages may have promoted speciation in various taxa. However, the timing, extent and direction of introgressive hybridization remain unknown in many cases. Here, we report a possible case in which repeated hybridization promoted divergence of Oryzias ricefishes (Adrianichthyidae) on Sulawesi, an island of Wallacea. Four Oryzias species are endemic to the Malili Lake system in central Sulawesi, which is composed of five tectonic lakes; of these, one lake is inhabited by two species. Morphological and population genomic analyses of genome-wide single-nucleotide polymorphisms revealed that these two sympatric species are phylogenetically sister to but substantially reproductively isolated from each other. Analyses of admixture and comparison of demographic models revealed that the two sympatric species experienced several substantial introgressions from outgroup populations that probably occurred soon after they had secondary contact with each other in the lake. However, the ratio of migrants from the outgroups was estimated to be different between the two species, which is consistent with the hypothesis that these introgressions aided their divergence or prevented them from forming a hybrid swarm. Repeated lake fragmentations and fusions may have promoted diversification of this freshwater fish species complex that is endemic to this ancient lake system.

中文翻译：

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苏拉威西亚湖系统中的物种分化和重复的古代杂交。

越来越多的实证研究表明，远距离谱系之间的杂交可能促进了各种分类群的物种形成。然而，在许多情况下，渐进杂交的时间、程度和方向仍然未知。在这里，我们报告了一个可能的案例，其中重复杂交促进了华莱士岛苏拉威西岛稻鱼（Adrianichthyidae）的分化。四种 Oryzias 物种是苏拉威西中部马里湖系统的特有物种，该系统由五个构造湖组成；其中，一个湖居住着两个物种。全基因组单核苷酸多态性的形态学和种群基因组分析表明，这两个同域物种在系统发育上是姐妹，但在生殖上彼此隔离。对混合物的分析和人口统计模型的比较表明，这两个同域物种经历了外群种群的几次大量渗入，这可能发生在它们在湖中第二次接触后不久。然而，估计来自外群的移民比例在两个物种之间是不同的，这与这些基因渗入有助于它们的分化或阻止它们形成混合群的假设一致。反复的湖泊破碎和融合可能促进了这个古老湖泊系统特有的淡水鱼类物种复合体的多样化。