Steroid hormones play key roles in the development of gender differences in behavior, part of the process known as sexual differentiation. In many vertebrates, one such hormone-mediated difference is that males often are more aggressive than females. Features that rarely occur in combination, but are found in Sceloporus lizards, make them an ideal model for the integrative study of variation in hormonal mediation of aggression: They are a set of closely related species that (1) vary reliably in male-female differences in levels of aggression; (2) have unambiguous aggressive behaviors; (3) are amenable to hormone manipulations both in the laboratory and under free-living conditions, and to both perinatal and adult hormone manipulations, and (4) can be reared to adulthood in the laboratory and will exhibit the full array of typical adult behavior, including aggression. Dr. Hews will examine the neuroendocrine basis of dramatic differences among three Sceloporus species in the morphological color traits used in signaling territorial aggression and in the degree to which males and females differ in levels of aggression. This Research Planning Grant will enable Dr. Hews to (1) establish levels of aggression in free-living males and females of the three study species, using a well-established testing paradigm, (2) develop a laboratory paradigm for testing aggression in the three species, (3) obtain breeding-season blood samples for radioimmunoassay to assess plasma hormone levels (data needed for future experiments in which implants manipulate hormone level in a physiological manner), and (4) determine the size of a hormone implant needed to deliver a maximum physiological level.
