Anthropology, Rutgers University
Saturday 2:15-2:30, Grand Ballroom II
The Challenge Hypothesis (Wingfield et al., 1990) posits a correlation between male androgen levels and mating system, male-male aggression in a sexual context, and parental effort. This model has received support across a variety of taxa, including primates. Most primate studies refer to multi-male societies with high levels of male-male aggression and limited paternal care. To expand this dataset, I tested predictions of the Challenge Hypothesis in a population of wild siamangs (Symphalangus syndactylus), small apes characterized by intense territoriality, monogamous/polyandrous grouping, dominance relationships between co-resident males, and varying amounts of paternal behavior. I collected behavioral data on 11 siamang groups (five one-male, six two-male groups) between August 2007 and April 2009. Over a 13-month period, I collected 747 fecal samples from 21 adult males, and subsequently radio-immunoassayed testosterone levels. Results show no effect of grouping, rank, frequency of intragroup aggression and intergroup encounters on male androgen levels. Testosterone levels were negatively correlated with paternal behavior. Highest testosterone values corresponded to a period of social instability (two attempts at supplanting a resident male). Males in two-male groups experienced higher rates of intragroup agonistic interactions and lower intergroup aggression than males in one-male groups. Results support the Challenge Hypothesis.
Research funded by the National Science Foundation (Grant ID 0726022) and Wenner-Gren Foundation (Gr. 7766).