Corticosterone Treatment Has Subtle Effects on Thermoregulatory Behavior and Raises Metabolic Rate in the New Zealand Common Gecko, Hoplodactylus maculatus

Baseline concentrations of adrenal glucocorticoids often vary substantially in wild vertebrates in the field. In at least one ectotherm, females of the New Zealand common gecko, Hoplodactylus maculatus, this variation in baseline (not stress‐induced) corticosterone appears to be correlated with variation in body temperature (T_b). We tested the hypothesis that elevated corticosterone affects thermoregulatory behavior so as to raise T_b and that, independently of an increase in T_b, corticosterone increases metabolic rate. Compared with geckos receiving placebo implants, those that received implants containing corticosterone displayed heat‐seeking behaviors, had a higher mean T_b in their home cages, and, at one time of day, selected a higher mean T_b in a thermal gradient. At a constant T_b, corticosterone‐treated geckos consumed oxygen at a rate approximately 50% higher than placebo geckos. This work has far‐reaching implications for a variety of physiological and ecological processes in ectotherms and suggests that corticosterone should be considered as a variable influencing T_b and metabolism in future studies.