Sex differences in androgen activation of complex courtship behaviour

Sexual dimorphism is common but evolutionarily labile in vertebrates. While it is well established that gonadal hormones exert considerable influence on the development and expression of sexual traits, studies of animals with exceptional sexually dimorphic neural or neuromuscular phenotypes are limited. We studied the extent to which androgen treatment of female golden-collared manakins, Manacus vitellinus, activates specific elements of the elaborate, acrobatic courtship behaviour characteristic of males. After 1 week, nonbreeding females and juvenile males given implants containing testosterone (T) were observed for 3 weeks in an outdoor aviary situated in the middle of Panamanian rainforest. T-treated males performed the full suite of documented masculine courtship behaviours, whereas T-treated females performed only a few of these behaviours and then at much lower rates than males. T treatment did increase aggressive behaviour to a similar degree in both males and females. These results suggest that neuromuscular systems encoding elements of male courtship as well as aggressive behaviour experience unique patterns of development from complete to limited to nonexistent sexual differentiation. The basis of these patterns represents a unique opportunity for study.