Assortative mating by genomic regions involved in plumage coloration in a rapid avian radiation

DI GIACOMO, ADRIÁN SANTIAGO; SAFRAN, REBECCA; BROWNE, MELANIE; TAYLOR, SCOTT; TURBEK, SHEELA; KOPUCHIAN, CECILIA; CAMPAGNA, LEONARDO

Pacific Grove

Congreso; Meeting of the American Society of Naturalists; 2020

American Society of Naturalists

Post-zygotic isolation often takes longer to evolve than the time to speciation of many taxa, and pre-mating isolation has therefore been proposed as a powerful reproductive barrier maintaining sympatric species early in divergence. However, the ease with which assortative mating can break down has called the importance of pre-mating isolation during incipient speciation into question. We combined whole-genome and double digest restriction-site associated DNA (ddRAD) data with fine-scale behavioral analyses to quantify assortative mating between two sympatric species of capuchino seedeaters (Sporophila hypoxantha and Sporophila iberaensis), which belong to a recent, rapid avian radiation characterized by striking differences in male plumage coloration and song despite remarkably little ecological or genomic divergence. The two species exhibit an extremely low level of background differentiation (genome-wide FST = 0.006)that is punctuated by three narrow regions of elevated genomic divergence. These peaks, ranging from 5-50 kb long,encompass 11 genes, two of which are known to be involved in the regulation of coloration. Though S. hypoxantha and S. iberaensis lack temporal or spatial barriers to reproduction and rates of extra-pair paternity were extremely high, we documented complete assortative mating by the genomic regions that underlie differences in male plumage patterning over the course of two breeding seasons. Given that females of the two species are phenotypically indistinguishable, our findings provide strong evidence that pre-mating isolation related to male sexual signaling may be sufficient to maintain species boundaries extremely early in divergence.