Social dominance in several species of lizards appears related to adrenal gland activity. The purpose of this study was to test whether the adrenal hormone corticosterone (CS) would inhibit the aggressive behavior of males of the lizard Anolis sagrei. Reproductively active males were randomly assigned to either CS or placebo (P) treatment groups or to an untreated stimulus male group. Both CS and P were administered in pellet form. Corticosterone pellets were designed to release approximately 4.8 μg of CS day. Initially (Day 1), treatment males were implanted subcutaneously with a single pellet of either CS or P. After 1 week (Day 8), behavior tests were staged between treatment males and untreated stimulus males. The behavior of treatment males in response to stimulus males was videotaped. Significantly fewer CS-treated males than P-treated males approached the stimulus males, erected a crest, or showed biting behavior. Corticosterone-treated males also displayed significantly less frequently than did P-treated males and gave fewer displays of a type associated with dominance. Mean combined testis weight at the end of the experiment was significantly less in CS-treated males than in P-treated males and spermatogenic activity in CS-treated males was reduced. Plasma testosterone in CS-treated males was non-detectable, whereas P-treated males had normal levels of this steroid. These results indicate that CS can inhibit male aggressive behavior and testicular function in a lizard and support the hypothesis that the behavior changes observed in subordinate animals following defeat in agonistic encounters may in part be due to increased plasma CS levels.
ASJC Scopus subject areas
- Endocrine and Autonomic Systems
- Behavioral Neuroscience