After establishing secondary contact, recently diverged populations may remain reproductively isolated or may hybridize to a varying extent depending on factors such as hybrid fitness and the strength of assortative mating. Here, we used genomic and phenotypic data from three independent contact zones between subspecies of the variable seedeater (Sporophila corvina) to examine how coloration and genetic divergence shape patterns of hybridization. We found that differences in plumage coloration are probably maintained by divergent selection across contact zones; however, the degree of plumage differentiation does not match overall patterns of hybridization. Across two parallel contact zones between populations with divergent phenotypes (entirely black vs. pied plumage), populations hybridized extensively across one contact zone but not the other, suggesting that plumage divergence is not sufficient to maintain reproductive isolation. Where subspecies hybridized, hybrid zones were wide and formed by later-generation hybrids, suggesting frequent reproduction and high survivorship for hybrid individuals. Moreover, contemporary gene flow has played an important role in shaping patterns of genetic structure between populations. Replicated contact zones between hybridizing taxa offer a unique opportunity to explore how different factors interact to shape patterns of hybridization. Overall, our results demonstrate that divergence in plumage coloration is important in reducing gene flow but insufficient in maintaining reproductive isolation in this clade, and that other factors such as divergence in song and time since secondary contact may also play an important role in driving patterns of reduced hybridization and gene flow.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics