Steroid hormone profiles and relative body condition of calling and satellite toads: implications for proximate regulation of behavior in anurans

Males of most anuran species (frogs and toads) vocalize to attract mates. However, individuals of many vocal species may also adopt alternative noncalling "satellite" tactics. Satellite males characteristically remain in close proximity to calling conspecifics and attempt to intercept incoming females attracted to advertising males. Emerson proposed that alternation between calling and noncalling behavior in anurans is mediated by a reciprocal interaction between circulating levels of corticosterone and androgens that is driven by depletion of energy reserves during vocalization. We tested this hypothesis by examining steroid hormone profiles and the relative body condition of calling and satellite Woodhouse's toads (Bufo woodhousii) and Great Plains toads (B. cognatus). Consistent with Emerson's hypothesis, callers had significantly higher circulating corticosterone levels and were in better condition than satellites. However, levels of testosterone and dihydrotestosterone did not differ significantly between satellites and callers, and we found no evidence that high levels of corticosterone had an inhibitory effect on androgen production in either species. These data thus support a relationship between corticosterone levels and depletion of energy reserves during bouts of vocalization but suggest that alternation between calling and satellite behavior may be associated with direct effects of corticosterone on brain vocal control centers. We propose a model that incorporates relationships among energy reserves, androgens, corticosterone, and arginine vasotocin-producing neurons in the telencephalon to explain transitions between calling and satellite tactics in toads.