Effects of steroid hormone interaction on activity and home-range size of male lizards.

Steroid hormones play a major role in influencing the physiology and behavior of all animals, including reptiles. Oftentimes, it is an interaction between two or more hormones that is ultimately responsible for the observed response or behavior. We designed a pair of field studies on adjacent communities of side-blotched lizards (Uta stansburiana) to provide insight into the interrelationship of testosterone (T) and corticosterone (B) in regulating aggressive behavior. On one site, males were implanted with either T or saline (S), while on the other site males received either two S implants or both a T and a B implant (T + B). T increased both activity (by 31%) and home-range size (by 150%), whereas S-implanted cohorts exhibited a reduction in both of these parameters (by 24 and 50%, respectively). However, when B was given in combination with T, not only were the positive effects of T eliminated, but there was a reduction in activity (31%) and home-range size (72%) similar to that reported in lizards that received B implants alone. S-implanted cohorts in the T + B experiment increased their activity and home-range size by 15 and 43%, respectively. Although these latter changes in the S-implanted males are not statistically significant, they are indicative of a compensatory increase similar to that seen in the T and previously reported B outcrop experiments. Taken together, these results illustrate that regulation of aggressive behavior is complicated, with both hormonal and social interactions playing critical roles in determining an individual's home-range size and, hence, reproductive success.