Change in sexual signalling traits outruns morphological divergence across an ecological gradient in the post‐glacial radiation of the songbird genus Junco

The relative roles of natural and sexual selection in promoting evolutionary lineage divergence remains controversial and difficult to assess in natural systems. Local adaptation through natural selection is known to play a central role in promoting evolutionary divergence, yet secondary sexual traits can vary widely among species in recent radiations, suggesting that sexual selection may also be important in the early stages of speciation. Here we compare rates of divergence in ecologically relevant traits (morphology) and sexually selected signaling traits (coloration) relative to neutral structure in genome-wide molecular markers, and examine patterns of variation in sexual dichromatism to explore the roles of natural and sexual selection in the diversification of the songbird genus Junco (Aves: Passerellidae). Juncos include divergent lineages in Central America and several dark-eyed junco (J. hyemalis) lineages that diversified recently as the group recolonized North America follow...