The adaptive radiations of East African cichlid fish in the Great Lakes Victoria, Malawi, and Tanganyika are well known for their diversity and repeatedly evolved phenotypes. Convergent evolution of melanic horizontal stripes has been linked to a single locus harboring the gene agouti-related peptide 2 (agrp2). However, where and when the causal variants underlying this trait evolved and how they drove phenotypic divergence remained unknown. To test the alternative hypotheses of standing genetic variation versus de novo mutations (independently originating in each radiation), we searched for shared signals of genomic divergence at the agrp2 locus. While we discovered similar signatures of differentiation at the locus level, the haplotypes associated with stripe patterns are surprisingly different. In Lake Malawi, the highest associated alleles are located within and close to the 5′ untranslated region of agrp2 and likely evolved through recent de novo mutations. In the younger Lake Victoria radiation, stripes are associated with two intronic regions overlapping with a previously reported cis-regulatory interval. The origin of these segregating haplotypes predates the Lake Victoria radiation since they are also found in more basal riverine and Lake Kivu species. This suggest that both segregating haplotypes were present as standing genetic variation at the onset of the Lake Victoria adaptive radiation with their more than 500 species and drove phenotypic divergence within the species flock. In summary, both new (Lake Malawi) or ancient (Lake Victoria) allelic variation at the same locus can fuel rapid and convergent phenotypic evolution.

中文翻译：

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等位基因变异的不同来源导致慈鲷鱼重复出现颜色模式差异。

维多利亚大湖、马拉维和坦噶尼喀的东非慈鲷鱼的适应性辐射以其多样性和反复进化的表型而闻名。黑色水平条纹的趋同进化与包含基因agouti 相关肽 2 ( agrp2 )的单个基因座有关。然而，这种特征背后的因果变异在何时何地进化以及它们如何导致表型差异仍然未知。为了测试固定遗传变异与从头突变（独立起源于每个辐射）的替代假设，我们在agrp2 上搜索了基因组差异的共享信号轨迹。虽然我们在基因座水平发现了类似的分化特征，但与条纹图案相关的单倍型却出人意料地不同。在马拉维湖中，关联度最高的等位基因位于agrp2的 5' 非翻译区域内并靠近该区域，并且可能是最近从头进化而来的突变。在较年轻的维多利亚湖辐射中，条纹与两个内含子区域相关，这些区域与先前报道的顺式调节间隔重叠。这些分离单倍型的起源早于维多利亚湖辐射，因为它们也存在于更基础的河流和基伍湖物种中。这表明，在维多利亚湖适应性辐射开始时，这两种分离单倍型均作为常设遗传变异存在，其 500 多个物种导致了物种群内的表型分化。总之，同一位点的新（马拉维湖）或古代（维多利亚湖）等位基因变异都可以促进快速和趋同的表型进化。