Data from: Are sympatrically speciating Midas cichlid fish special? Patterns of morphological and genetic variation in the closely related species Archocentrus centrarchus

Established empirical cases of sympatric speciation are scarce, although there is an increasing consensus that sympatric speciation might be more common than previously thought. Midas cichlid fish are one of the few substantiated cases of sympatric speciation, and they formed repeated radiations in crater lakes. In contrast, in the same environment, such radiation patterns have not been observed in other species of cichlids and other families of fish. We analyze morphological and genetic variation in a cichlid species (Archocentrus centrarchus) that co-inhabits several crater lakes with the Midas species complex. In particular, we analyze variation in body and pharyngeal jaw shape (two ecologically important traits in sympatrically divergent Midas cichlids) and relate that to genetic variation in mitochondrial control region and microsatellites. Using these four datasets, we analyze variation between and within two Nicaraguan lakes: a crater lake where multiple Midas cichlids have been described and a lake where the source population lives. We do not observe any within-lake clustering consistent across morphological traits and genetic markers, suggesting the absence of sympatric divergence in A. centrarchus. Genetic differentiation between lakes was low and morphological divergence absent. Such morphological similarity between lakes is found not only in average morphology, but also when analyzing covariation between traits and degree of morphospace occupation. A combined analysis of the mitochondrial control region in A. centrarchus and Midas cichlids suggests that a difference between lineages in the timing of crater lake colonization cannot be invoked as an explanation for the difference in their levels of diversification. In light of our results, A. centrarchus represents the ideal candidate to study the genomic differences between these two lineages that might explain why some lineages are more likely to speciate and diverge in sympatry than others.

已报道的同域物种形成（sympatric speciation）实证案例较为稀少，但学界越来越多的共识认为，同域物种形成的实际发生率可能远超此前的认知。迈达斯丽鱼（Midas cichlid）是少数确证的同域物种形成案例之一，它们在火山口湖中多次发生物种辐射演化。与之形成鲜明对比的是，在相同的火山口湖生境中，其他丽鱼科鱼类乃至其他鱼类类群均未观察到此类辐射演化模式。本研究针对一种与迈达斯丽鱼复合群共同栖息于多个火山口湖的丽体鱼——中丽体鱼（Archocentrus centrarchus），对其形态与遗传变异展开分析。具体而言，我们重点检测了其躯体与咽颌的形态变异——这两个性状正是同域分化的迈达斯丽鱼的关键生态适应性性状，并将该形态变异与线粒体控制区（mitochondrial control region）及微卫星标记（microsatellites）的遗传变异相关联。依托上述四类数据集，我们对两个尼加拉瓜湖泊中的种群展开了种群间与种群内的变异分析：其中一个火山口湖已发现多种迈达斯丽鱼物种，另一个湖泊则为该中丽体鱼源种群的栖息生境。研究未观察到跨形态性状与遗传标记的种群内聚类现象，表明中丽体鱼不存在同域分化过程。不同湖泊间的遗传分化程度较低，且未出现形态分化。湖泊间的形态相似性不仅体现在平均形态特征上，在性状间协变关系与形态空间占据度的分析中同样成立。对中丽体鱼与迈达斯丽鱼的线粒体控制区进行联合分析后发现，两谱系在火山口湖定殖时间上的差异，无法解释二者演化分化水平的差异。综上，本研究结果表明，中丽体鱼是探究两谱系间基因组差异的理想研究对象，此类差异或可解释为何部分类群更易发生同域物种形成与分化。