Tropical Biosphere Research Center, University of the Ryukyus, Okinawa, 903-0213, Japan.
Faculty of Social and Cultural Studies, Kyushu University, Fukuoka, 819-0395, Japan.
Evolution. 2019 Sep;73(9):1898-1915. doi: 10.1111/evo.13821. Epub 2019 Aug 27.
Sympatric speciation has been demonstrated in few empirical case studies, despite intense searches, because of difficulties in testing the criteria for this mode of speciation. Here, we report a possible case of sympatric speciation in ricefishes of the genus Oryzias on Sulawesi, an island of Wallacea. Three species of Oryzias are known to be endemic to Lake Poso, an ancient tectonic lake in central Sulawesi. Phylogenetic analyses using RAD-seq-derived single nucleotide polymorphisms (SNPs) revealed that these species are monophyletic. We also found that the three species are morphologically distinguishable and clearly separated by population-structure analyses based on the SNPs, suggesting that they are reproductively isolated from each other. A mitochondrial DNA chronogram suggested that their speciation events occurred after formation of the tectonic lake, and existence of a historical allopatric phase was not supported by coalescent-based demographic inference. Demographic inference also suggested introgressive hybridization from an outgroup population. However, differential admixture among the sympatric species was not supported by any statistical tests. These results all concur with criteria necessary to demonstrate sympatric speciation. Ricefishes in this Wallacean lake provide a promising new model system for the study of sympatric speciation.
尽管经过了密集的搜索，但由于难以测试这种物种形成模式的标准，仅有少数实证案例研究证明了同域物种形成的存在。在这里，我们报告了华莱士地区苏拉威西岛上的稻鱼属鱼类中可能存在的同域物种形成案例。已知有三种稻鱼属鱼类是苏拉威西中部古老构造湖波索湖的特有种。基于 RAD-seq 衍生的单核苷酸多态性 (SNP) 的系统发育分析表明，这些物种是单系的。我们还发现，这三个物种在形态上是可区分的，并且基于 SNP 的种群结构分析清楚地将它们分开，表明它们彼此之间存在生殖隔离。线粒体 DNA 时标表明，它们的物种形成事件发生在构造湖形成之后，并且没有证据支持基于合并的种群动态推断存在历史的异域阶段。种群动态推断还表明，来自一个外群群体的渐渗杂交。然而，任何统计检验都不支持同域物种之间的差异混合。这些结果都符合证明同域物种形成所需的标准。这个华莱士湖中的稻鱼属鱼类为同域物种形成的研究提供了一个很有前途的新模型系统。
