UNIDIRECTIONAL SPREAD OF SECONDARY SEXUAL PLUMAGE TRAITS ACROSS AN AVIAN HYBRID ZONE

Theory predicts that traits under positive selection can rapidly cross a hybrid zone in spite of a substantial barrier to neutral gene flow between hybridizing taxa. An avian hybrid zone between Manacus candei (white-collared manakin) and M. vitellinus (golden-collared manakin) i s reported here that displays an unusual pattern of noncoincident clin es. Male secondary sexual traits of M. vitellinus have spread into pop ulations that are genetically and morphometrically like M. candei. The se birds have a lek breeding system in which male mating success is hi ghly skewed, suggesting that sexual selection is driving male sexual t raits across the zone.