Hybridization Between Neotropical Primates with Contrasting Sexual Dichromatism

Hybridization is relatively well documented among Old World primates, but poorly investigated among New World monkeys. We investigated hybridization between the sexually dichromatic howlers Alouatta caraya and Alouatta guariba clamitans, whose lineages diverged ca. 5 million years ago. These taxa show allopatric distributions with a few recently discovered narrow contact zones. We collected 169 individual fecal samples of A. caraya and A. g. clamitans within (N=121) and outside (N=48) two contact zones in southern Brazil. We used mtDNA and Y-chromosome (SRY gene) sequences, and three diagnostic microsatellite loci to investigate their parental origin. We found 33 individuals (27%) with evidence of hybrid origin in the contact zones. Thirteen individuals presented mtDNA of A. caraya origin and Y-chromosome of A. g. clamitans origin and eight individuals have the opposite combination of markers. We assigned the hybrid origin of the remaining 12 individuals based on the discrepancy between their uniparental markers and microsatellite data, or a combination of diagnostic alleles of both species. This is the first evidence of hybridization between A. caraya and A. g. clamitans. We hypothesize that this hybridization is bidirectional, ancient, and geographically wider than previously thought. The confirmation of hybridization in our contact zones provides evidence that interspecific differences in male coat color do not function as prezygotic barriers. We concluded that sexual selection by means of mate recognition is a weak explanation for the evolution of sexual dichromatism in these species. Finally, our system highlights the great complexity of this mechanism and its potential for the evolution and diversification of primates.