Abstract
Social networks capture the occurrence, direction and strength of pairwise interactions among individual animals in a group. Their structure has proven to be a key determinant of the patterns of parasite transmission and disease spread within groups. In contrast, little is known about how parasites themselves may have influenced the evolution of host social networks. Here, we use a comparative analysis among primate species to test the hypothesis that strong selective pressures exerted by parasites may have favoured the evolution of social network patterns that reduce the probability of infection. After controlling for variation in study effort and for host phylogeny, we find that social networks in primate species infected by multiple species of contagious (contact- or proximity-transmitted) parasites present slightly different topology than those in primates exposed to fewer parasites. In particular, we uncovered a positive relationship across primate species between parasite species richness and degree heterogeneity, that is, the coefficient of variation in number of social contacts per individual. While correlative evidence is insufficient to demonstrate causality, this result provides some support for our hypothesis on the link between host sociality and parasitism: host social networks shape patterns of intra-group parasite transmission, whereas selective pressures from parasites may in turn influence the structure of host social networks. Significance statement Patterns of interactions among animals within a group form a social network, which provides a map of the possible routes of parasite transmission and disease spread within the group. At the same time, it is possible that selective pressures from the parasites themselves have shaped animal social networks, with species experiencing strong pressures from parasites (i.e. infected by many species of contagious parasites) having evolved social networks that limit the risk of infection for individual group members. We provide correlative evidence for the possible evolutionary influence of parasitism on social network structure, using a comparison among primate species. Our study provides a reversed narrative to the usual one in which social network structure drives infection.