1Department of Evolutionary Anthropology, Duke University, 2Population Biology, Ecology and Evolution Graduate Program, Emory University, 3Department of Psychology, Franklin & Marshall College, 4Department of Veterinary Population Medicine, University of Minnesota, 5Department of Environmental Sciences, Emory University, 6Department of Environmental Health, Rollins School of Public Health, Emory University
April 14, 2016 10:45, A 706/707
Increased risk of pathogen transmission through close proximity and physical contact is a well-documented cost of sociality. For highly social animals like primates, however, affiliative social contact is an integral part of group life and can have beneficial effects on health through its role in ameliorating stress. The tradeoff between costs and benefits of social contact has implications for the evolution of social structures and relationships within social groups, yet remains poorly understood. Here, we test whether variation in social behavior among wild chimpanzees (Pan troglodytes) is associated with intestinal parasite infections, which recent studies suggest can be transmitted through social contact. Using a dataset of 385 fecal samples from 43 adult males and females of the Kasakela community in Gombe National Park, we modelled individual mean parasite richness over a three-year period with a generalized estimating equations approach. As potential predictors of parasite richness we considered number of social partners, mean party size, strength of social connections, party association and grooming network centrality, time spent grooming, age, and dominance rank. We found that, all else being equal, more gregarious individuals had more parasites, and individuals with stronger grooming bonds had fewer parasites. Effect sizes varied by sex. Our results suggest a negligible risk of exposure to infective parasite stages through grooming, contrasting to conclusions reached by recent studies in other primates. Instead, strong grooming bonds came with tangible health benefits, particularly for females, while gregariousness carried health costs, particularly for males. We discuss potential mechanisms behind these patterns.
Funding provided by The Jane Goodall Institute, National Science Foundation (IOS LTREB-1052693), National Institutes of Health (R01-AI058715), Morris Animal Foundation (MAF D09ZO-041), Emory University Global Health Institute, and Duke University.