9222763 Levin The purpose of this project is to investigate the origin of sex differences in social behavior by examining bird song. Bird studies have focused on species in which only males sing, have identified specific areas in male brains that control song behavior, and have shown that these areas are turned on and off by testosterone. Non-singing females of these species don't have these well-developed brain regions and lack significant levels of testosterone in their blood. Dr. Levin will expand this understanding of the origin of sex differences in behavior by looking at a tropical species in which both sexes sing, in which sex differences are maintained in songs. She plans to raise young birds hearing only one male song, only female song, the song of both sexes, or no song. Examining what these birds learn to sing and how their hormone levels change during song learning will help reveal the roles played by hormones and social role models in the development of sex differences in song. She will test any suggested role of hormones in song development by examining song development in surgically castrated birds. While the issue of the origin of sex differences in behavior, particularly in humans, is a topic of much interest, it is difficult to address in a rigorous, systematic fashion. Studies of bird species offer a unique opportunity to do so because the avian nervous system is so amenable to study and because of the vast array of species differences in the relative roles played by males and females, population differences in sex-species behaviors within one species, and individual differences within a population that can be found among birds. Avian systems have been successfully used to generate and test proposed models in other areas of interest, such as the inter-relationships of hormones, aggression, and social environment, and the results of these studies have proven to be remarkably parallel to those from studies of primates and other ve rtebrates. Thus, it seems likely that simply by prudently choosing appropriate species, we can exploit avian systems to reveal the mechanisms that might be associated with the process of sexual differentiation in the behavior of vertebrates.
