Glucocorticoids, androgens, testis mass, and the energetics of vocalization in breeding male frogs

Male advertisement vocalization in frogs is known to be one of the energeti cally most expensive activities of ectothermic vertebrates. Glucocorticoids have marked effects on energy metabolism, and, generally, plasma concentra tions of glucocorticoids increase during the course of prolonged exercise b outs. Androgen concentrations are also known to vary considerably among bre eding male frogs. Intraspecific and interspecific comparisons were used to test for a relationship among androgen concentration, corticosterone concen tration, testis mass, and the energetics of vocalization in natural populat ions of calling male frogs. The results of this study indicate that: (I) in traspecific variation in androgen and corticosteroid concentrations in bree ding male frogs is positively correlated as a result of both interindividua l variation in the amount of performed vocalization and the relationship be tween calling effort of an individual male and the level of calling in othe r males, (2) interspecific variation in corticosteroid concentration of cal ling male frogs is correlated with the relative energy expended in the spec ies-specific vocalization, and (3) when differences in testis mass are cont rolled for, vocalization effort is correlated with androgen concentration a mong species of breeding male frogs. These findings are in contrast to some recent work reported from laboratory experiments on calling frogs. (C) 200 1 Academic Press.