Harem-holding males do not rise to the challenge: androgens respond to social but not to seasonal challenges in wild geladas

摘要

The challenge hypothesis has been enormously successful in predicting inter specific androgen profiles for vertebrate males. Nevertheless, in the absence of another theoretical framework, many researchers ‘retrofit’ the challenge hypothesis, so that its predictions also apply to intra specific androgen comparisons. We use a wild primate, geladas ( Theropithecus gelada ), to illustrate several considerations for androgen research surrounding male contests that do not necessarily fit within the challenge hypothesis framework. Gelada society comprises harem-holding males (that can mate with females) and bachelor males (that cannot mate with females until they take over a harem). Using 6 years of data from known males, we measured androgens (i.e. faecal testosterone (fT) metabolites) both seasonally and across specific male contests. Seasonal androgen variation exhibited a very different pattern than variation resulting from male contests. Although harem-holding males had higher testosterone levels than bachelors across the year, bachelors had higher testosterone during the annual ‘takeover season’. Thus, harem-holding males did not ‘rise to the challenge’ exactly when needed most. Yet, androgen profiles across male contests indicated that both sets of males exhibit the expected fT rise in response to challenges. Results from male geladas also support the idea that the context before (e.g. male condition) and after (e.g. contest outcome) a contest are critical variables for predicting hormones and behaviour.