1School of Human Evolution and Social Change, Arizona State University, 2Department of Evolutionary Anthropology, Duke University
April 14, 2016 8:30, A 706/707
Alpha male chimpanzees have high reproductive success, yet body mass does not predict rank, begging the question: How do individuals acquire and maintain rank? One hypothesis is that large and small alphas exhibit distinct dominance styles that are suited to their body size. Indeed, there is evidence that body size affects how much and how equitably alpha males groom others. Here, we use 33 years of behavioral data from Gombe National Park to investigate mating behavior as a correlate of dominance style among eight alpha male chimpanzees. Using a generalized linear model to control for party composition and relatedness to the female, we found that alphas varied in the degree to which they monopolized matings with parous, sexually receptive females (mean ± SD = 21.6 ± 8.0% of all matings; range = 12.4 - 33.3%). This variation could reflect an alpha’s tolerance for others’ mating attempts (concession model), potentially in exchange for coalitionary support. Alternatively, this variation might simply reflect the degree to which each alpha is able to monopolize access to females (tug-of-war model). In preliminary analyses, we found no systematic relationship between either dominance (as measured by Elo ratings) or body size (relative to other adult males) and an alpha’s degree of mating monopolization, although the most dominant and largest alpha was most successful at monopolizing matings. Further work on monopolization during the periovulatory period, and on grooming relationships and coalitions, is needed to test these hypotheses.
Funding provided by the Jane Goodall Institute, the National Science Foundation (9021946, 9319909, 0452315, 1052693, 0431141) and the National Institutes of Health (R01-AI058715, R00-HD057992).