Gregariousness is associated with parasite species richness in a community of wild chimpanzees

Increased risk of pathogen transmission through proximity and contact is a well-documented cost of sociality. Affiliative social contact, however, is an integral part of primate group life and can benefit health. Despite its importance to the evolution and maintenance of sociality, the tradeoff between costs and benefits of social contact for group-living primate species remains poorly understood. To improve our understanding of this interplay, we used social network analysis to investigate whether contact via association in the same space and/or physical contact measured through grooming were associated with helminth parasite species richness in a community of wild chimpanzees ( Pan troglodytes schweinfurthii ). We identified parasite taxa in 381 fecal samples from 36 individuals from the Kasekela community of chimpanzees in Gombe National Park, Tanzania, from November 1, 2006, to October 31, 2012. Over the study period, eight environmentally transmitted helminth taxa were identified. We quantified three network metrics for association and grooming contact, including degree strength, betweenness, and closeness. Our findings suggest that more gregarious individuals—those who spent more time with more individuals in the same space—had higher parasite richness, while the connections in the grooming network were not related to parasite richness. The expected parasite richness in individuals increased by 1.13 taxa (CI: 1.04, 1.22; p = 0.02) per one standard deviation increase in degree strength of association contact. The results of this study add to the understanding of the role that different types of social contact play in the parasite richness of group-living social primates. Significance statement Parasite infections reveal costs of group living among wild animal populations. We studied the relationship between sociality and parasite transmission by assessing whether variation in social behavior among wild chimpanzees is associated with the number of unique helminth parasites detected in individual fecal samples. Our findings revealed that associating in the same shared space, but not grooming contact, is related to higher parasite richness. These findings improve our understanding of the complex interplay of parasitism and sociality with important implications for parasite transmission patterns in host species with flexible grouping patterns.