Data from: Rapid postglacial diversification and long-term stasis within the songbird genus Junco: phylogeographic and phylogenomic evidence

Natural systems composed of closely-related taxa that vary in the degree of phenotypic divergence and geographic isolation, provide an opportunity to investigate the rate of phenotypic diversification and the relative roles of selection and drift in driving lineage formation. The genus Junco (Aves: Emberizidae) of North America includes parapatric northern forms that are markedly divergent in plumage pattern and color, in contrast to geographically isolated southern populations in remote areas that show moderate phenotypic divergence. Here, we quantify patterns of phenotypic divergence in morphology and plumage color, and use mitochondrial DNA genes, nuclear introns, and genome-wide SNPs to reconstruct the demographic and evolutionary history of the genus to infer relative rates of evolutionary divergence among lineages. We found that geographically isolated populations have evolved independently for hundreds of thousands of years despite little differentiation in phenotype, in sharp contrast to phenotypically diverse northern forms, which have diversified within the last few thousand years as a result of the rapid postglacial recolonization of North America. SNP data resolved young northern lineages into reciprocally monophyletic lineages, indicating low rates of gene flow even among closely related parapatric forms, and suggesting a role for strong genetic drift or multifarious selection acting on multiple loci in driving lineage divergence. Juncos represent a compelling example of speciation-in-action, where the combined effects of historical and selective factors have produced one of the fastest cases of speciation known in vertebrates.

由亲缘关系密切的类群组成的自然系统，其表型分化程度与地理隔离程度各不相同，为研究表型多样化速率，以及自然选择和遗传漂变在驱动谱系形成中的相对作用提供了绝佳研究契机。北美洲的灯草鹀属（Junco，鸟纲：鹀科）包含邻域分布的北部类群，这类群在羽色图案与体色上存在显著分化；与之形成鲜明对比的是，偏远区域的地理隔离南部种群仅表现出中等程度的表型分化。本研究量化了形态学与羽色的表型分化模式，并利用线粒体DNA基因、核内含子以及全基因组单核苷酸多态性（Single Nucleotide Polymorphism, SNPs）重构了该属的种群历史与演化历史，以推断不同谱系间的演化分化相对速率。研究发现，尽管表型分化程度极低，地理隔离的种群已独立演化数十万年；这与表型多样的北部类群形成鲜明反差——后者因北美冰期后快速再定植，在数千年内便完成了多样化演化。单核苷酸多态性数据将年轻的北部谱系解析为相互单系类群，表明即便在亲缘关系密切的邻域类群间，基因流水平也极低；这暗示强遗传漂变或作用于多基因座的多向选择，在驱动谱系分化中发挥了关键作用。灯草鹀属是极具说服力的正在进行中的物种形成实例，历史因素与选择因素的共同作用造就了脊椎动物中已知演化速度最快的物种形成事件之一。