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Data from: Maintenance of local adaptation despite gene flow in a coastal songbird

Clark, Jonathan D.1; Luther, David A.1; Benham, Phred M.2; Maldonado, Jesus E.3; Lim, Haw Chuan1

Published Apr 18, 2022 on Dryad. https://doi.org/10.5061/dryad.ghx3ffbr5

Data files

Apr 19, 2022 version files 23.58 MB
Apr 18, 2022 version files 23.58 MB

Abstract

Adaptation to local environments is common in widespread species and the basis of ecological speciation. The song sparrow (Melospiza melodia) is a widespread, polytypic passerine that occurs in shrubland habitats throughout North America. We examined the population structure of two parapatric subspecies that inhabit different environments: the Atlantic song sparrow (M. m. atlantica), a coastal specialist; and the eastern song sparrow (M. m. melodia), a shrubland generalist. These populations lacked clear mitochondrial population structure, yet coastal birds formed a distinct nuclear genetic cluster. We found weak overall genomic differentiation between these subspecies, suggesting either recent divergence, extensive gene flow, or a combination thereof. There was a steep genetic cline at the transition to coastal habitats, consistent with isolation by environment (IBE), not isolation by distance (IBD). A phenotype under divergent selection, bill size, varied with the amount of coastal ancestry in transitional areas, but larger bill size was maintained in coastal habitats regardless of ancestry, further supporting a role for selection in the maintenance of these subspecies. Demographic modeling suggested a divergence history of limited gene flow followed by secondary contact, which has emerged as a common theme in adaptive divergence across taxa.