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, a nuclear intron, 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.