Assortative Mating by Plumage Coloration Genes in an Incipient Avian Radiation

SHEELA P. TURBEK; CECILIA KOPUCHIAN; LEONARDO CAMPAGNA; MELANIE BROWNE; REBECCA J SAFRAN; ADRIAN S. DI GIACOMO; SCOTT A TAYLOR

Virtual

Congreso; VII North American Ornithological Conference; 2020

Post-zygotic isolation often takes longer to evolve thanthe time to speciation of many taxa, and pre-matingisolation has therefore been proposed as a powerful re-productive barrier maintaining sympatric species earlyin divergence. However, the ease with which assor-tative mating can break down has called into questionthe importance of pre-mating isolation during incipientspeciation. We combined whole-genome and doubledigest restriction-site associated DNA (ddRAD) datawith fine-scale behavioral analyses from two years ofdetailed field study to quantify assortative mating be-tween two sympatric species of capuchino seedeaters(Sporophila hypoxantha and Sporophila iberaensis).Capuchino seedeaters comprise a recent, rapid avianradiation characterized by striking differences in maleplumage coloration and song despite remarkably lit-tle ecological or genomic divergence. We found thatthe two species exhibit an extremely low level of back-ground differentiation (genome-wide Fst = 0.006) thatis punctuated by three narrow regions of elevated ge-nomic divergence. These peaks, ranging from 30-50 kblong, encompass 11 genes, two of which are known tobe involved in the regulation of coloration. Though S.hypoxantha and S. iberaensis lack temporal or spatialbarriers to reproduction, and the rate of extra-pair pa-ternity was extremely high, we documented completeassortative mating with regard to both social and extra-pair mates by the genomic regions that underlie differ-ences in male plumage patterning. Given that femalesof the two species are phenotypically indistinguishable,our findings provide strong evidence that pre-matingisolation related to male sexual signaling may be suf-ficient to maintain species boundaries extremely earlyin divergence.