Mate choice influences differential introgression in a hybrid zone

Hybrid zones are widely recognized as important sources of genetic variation, and conduits for the exchange of genes from one species to another. How and which traits move, or introgress, is an important area of study in evolutionary biology. A hybrid zone between two manakin (Pipridae) species, Manacus candei and Manacus vitellinus, exists in Bocas del Toro Province, in western Panama. The hybrid zone is unique in that the plumage genes of Manacus vitellinus introgress up to 50 km beyond the genetic center of the hybrid zone, into populations that are morphologically and genetically similar to M. candei. M.vitellinus males are more aggressive than Manacus candei males in mixed leks where both species occur. If M. candei females preferred males with M. vitellinus plumage traits, introgression of M. vitellinus plumage genes would be explained by both intra- and inter-sexual selection. Manacus spp. have a lek mating system; males perform elaborate, acrobatic courtship displays on small arenas on the forest floor, producing loud ‘wingsnaps’ and maximizing the visibility of their colored throat feathers. We have recently shown that display performance is associated with female preference in M. vitellinus, with females perferring males that perform certain moves faster. Thus, we hypothesized that female choice based on courtship display drives asymmetrical trait introgression. We studied whether display performance differs between the two species. Using high speed videography to film courtship displays of males of the two species, we compared them for those traits which in M. vitellinus are correlated to female preference. Contrary to our expectations, we found that M. candei males outperform M. vitellinus males. We propose that vitellinus-like plumage is preferred by females, but only when it recombines with the candei morphometric background, and hence, the superior display ability of M. candei.