Assortative Mating by Plumage Coloration Genes in an Incipient Avian Radiation

TURBEK, SHEELA; BROWNE, MELANIE; DI GIACOMO, ADRIÁN S.; KOPUCHIAN, CECILIA; SAFRAN, REBECA; TAYLOR, SCOTT; CAMPAGNA, LEONARDO

Congreso; VII North American Ornithological Conference; 2020

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 into question the importance of pre-mating isolation during incipient speciation. We combined whole-genome and double digest restriction-site associated DNA (ddRAD) datawith fine-scale behavioral analyses from two years of detailed field study to quantify assortative mating between two sympatric species of capuchino seedeaters(Sporophila hypoxantha and Sporophila iberaensis). Capuchino seedeaters comprise a recent, rapid avian radiation characterized by striking differences in maleplumage coloration and song despite remarkably little ecological or genomic divergence. We found that the two species exhibit an extremely low level of backgrounddifferentiation (genome-wide Fst = 0.006) that is punctuated by three narrow regions of elevated genomic divergence. These peaks, ranging from 30-50 kblong, 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 spatialbarriers to reproduction, and the rate of extra-pair paternity was extremely high, we documented complete assortative mating with regard to both social and extrapair mates by the genomic regions that underlie differences in male plumage patterning. 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.