Data from: Genomics of rapid ecological divergence and parallel adaptation in four tidal marsh sparrows

Theory suggests that different taxa having colonized a similar,
challenging environment will show parallel or lineage-specific adaptations
to shared selection pressures, but empirical examples of parallel
evolution in independent taxa are exceedingly rare. We employed
comparative genomics to identify parallel and lineage-specific responses
to selection within and among four species of North American sparrows that
represent four independent, post-Pleistocene colonization events by an
ancestral, upland subspecies and a derived salt marsh specialist. We
identified multiple cases of parallel adaptation in these independent
comparisons following salt marsh colonization, including selection on
twelve candidate genes linked to osmoregulation. In addition to detecting
shared genetic targets of selection across multiple comparisons, we found
many novel, species-specific signatures of selection, including evidence
of selection on loci associated with both physiological and behavioral
mechanisms of osmoregulation. Demographic reconstructions of all four
species highlighted their recent divergence and small effective population
sizes, as expected given their rapid radiation into saline environments.
Our results highlight the interplay of both shared and lineage-specific
selection pressures in the colonization of a biotically and abiotically
challenging habitat and confirm theoretical expectations that steep
environmental clines can drive repeated and rapid evolutionary
diversification in birds.