Sympatric speciation is considered to be difficult without the coupling between ecological traits that allow resource partitioning and reproductive traits that allow assortative mating. Such "magic traits" are known to be involved in most of the compelling examples of sympatric speciation. In this study, we report a possible case of sympatric speciation without magic traits. Three species of ricefish (genus Oryzias) are suggested to have diverged sympatrically within Lake Poso, an ancient lake in Sulawesi. An analysis of genome-wide single-nucleotide polymorphisms showed that these three species are reproductively isolated from each other throughout the lake. Stable isotope analyses revealed that the three species use different food resources, which reflect differences in their feeding morphologies (gill rakers and digestive tracts) and feeding sites. Field and laboratory observations showed that O. nebulosus and O. orthognathus share a mating habitat of cobbles, where they scatter fertilized eggs, whereas this site is never used by O. nigrimas, indicating that assortative mating is partly achieved by spatial isolation. The small, less-adhesive eggs of O. nebulosus and O. orthognathus probably reflect their adaptation to spawning on cobble beaches. Laboratory mating experiments showed strong prezygotic isolation between O. nebulosus and O. orthognathus, which is achieved by strong species recognition presumably by both sexes based on species-specific mating dances and nuptial coloration. In summary, the assortative mating of O. nebulosus and O. orthognathus is probably not coupled to resource partitioning. We discussed how sympatric speciation among these species might have been achieved even without magic traits.

中文翻译：

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在华莱士古湖中，资源分配与同域发散的稻鱼的分类交配不相关。

如果没有允许资源分配的生态特征和允许分类交配的生殖特征之间的耦合，同域物种形成被认为是困难的。众所周知，这种“神奇特征”与大多数同域物种形成的引人注目的例子有关。在这项研究中，我们报告了一个没有魔法特征的同域物种形成的可能案例。三种稻鱼（Oryzias 属）被认为在苏拉威西岛的一个古老湖泊波索湖内同域分流。对全基因组单核苷酸多态性的分析表明，这三个物种在整个湖泊中彼此生殖隔离。稳定同位素分析表明，这三个物种使用不同的食物资源，这反映了它们摄食形态（鳃耙和消化道）和摄食部位的差异。野外和实验室观察表明 O. nebulosus 和 O. orthognathus 共享一个鹅卵石交配栖息地，在那里它们散布受精卵，而 O. nigrimas 从不使用该地点，这表明混合交配部分是通过空间隔离实现的。O. nebulosus 和 O. orthognathus 的小、粘性较小的卵可能反映了它们对在鹅卵石海滩产卵的适应。实验室交配实验表明 O. nebulosus 和 O. orthognathus 之间存在很强的合子前隔离，这是通过基于物种特定的交配舞蹈和婚礼着色的两性的强烈物种识别来实现的。总之，O. nebulosus 和 O. orthognathus 可能与资源分区无关。我们讨论了即使没有魔法特征，这些物种之间的同域物种形成是如何实现的。