Hormonal and social correlates of courtship signal quality and behaviour in male green treefrogs

Circulating hormone levels often vary considerably among males competing for mates, but how thisvariation affects the signalling phenotype is poorly understood. In the green treefrog, Hyla cinerea, malescompeting for mates engage in vocal contests that increase circulating levels of the adrenal glucocor-ticoid corticosterone (CORT) and decrease androgens in contest losers, who characteristically adopt anoncalling ‘satellite’ mating tactic. We previously showed that CORT administration to calling malesreduces vocal effort and increases the probability of satellite behaviour during simulated territorial in-trusions, suggesting that elevated CORT compromises vocal quality and decreases the propensity to callin a context-dependent manner. However, the extent to which these effects reflect variation in vocalbehaviour of males in natural choruses is unclear. Here, we examined how hormone levels, social contextand other potential determinants of vocalization, including body size and condition, relate to vocal at-tributes and behaviour in calling males and in associated satellites after removal of calling ‘host’ males.Results revealed that satellites had higher CORT and lower androgens and were smaller and in poorercondition than host males. Host removal resulted in vocalization in 74% of satellites. These males investedless effort in vocalization than hosts, and CORT level best explained these differences. The remaining 26%of satellites did not vocalize after host removal and had lower androgens than satellites that vocalized.Results provide support for context-dependent effects (i.e. host presence/absence) of elevated CORT onthe probability of vocalization and link high CORT to reduced vocal quality. In contrast, low androgenswere associated with a low probability of vocalization regardless of social context, and androgen levelwas a poor predictor of vocal attributes. Our results link high CORT and low androgens to variation insignalling quality and behaviour that potentially reduces the probability of attracting females.