1Department of Anthropology, University of Michigan, 2Department of Psychology, University of Michigan, 3Department of Ecology and Evolutionary Biology, University of Michigan
Friday 8:15-8:30, Ballroom A
Among male vertebrates, the challenge hypothesis predicts that seasonal patterns in androgen secretion vary in accordance with mating system, male-male competition, and paternal care. For example, in male primates competition for dominance rank is associated with increases in androgen levels. For reproductive success, gelada (Theropithecus gelada) males must first overthrow a dominant leader for access to a unit of females (“takeover”) and then, as the new leader of that unit, fend off rival males. Here, we examine the social and seasonal factors contributing to variation in male gelada androgen levels using noninvasive fecal samples (N=2730 samples and 133 males) collected over 6 years (2006-2011). We found a strong seasonal pattern in fecal testosterone metabolites (fT) for all males, with peak fT levels at the end of the rainy season when food is most abundant. Although leader males exhibited the highest levels of fT overall, bachelor males exhibited significantly higher fT levels across a few months each year characterized by a high rate of takeovers. Moreover, bachelors were more likely to engage in and escalate aggressive contests with leader males during this “takeover season”. Our results suggest that bachelors may be maximizing the likelihood of a successful takeover by challenging leader males when their fT levels are lowest.
Funding for this research was provided by the National Science Foundation (BCS-0715179, BCS-0962160, BCS-0962118, and Graduate Research Fellowship Program), the Leakey Foundation, the U.S. Fulbright Program, and the University of Michigan.