Abstract
The relationship between social interactions and infectious disease transmission has long been suggested to produce an evolutionary tradeoff between sociality and individual fitness (e.g. Freeland 1976; 1979). Because primates are among the most social of animal taxa, this relationship is hypothesized to have played an important role in their social evolution. Grooming, a behavior that evolved in defense of external parasitism but also serves a vital social function, may additionally provide a direct mechanism for recruitment of certain parasitic organisms with direct life cycles. While there exists strong theoretical evidence, backed by a growing body of empirical data, to support the importance of social contact in transmission of various micro-parasites (e.g. viruses and bacteria), few studies have empirically investigated the potential link between social grooming and the acquisition of directly transmitted macro-parasitic organisms, such as intestinal nematodes. Here, we use a Social Network Analysis (SNA) framework to examine the relationship between grooming behavior, social rank, and nematode parasite transmission among wild Japanese macaques (Macaca fuscata yakui) on Yakushima Island. We have previously shown that host traits do mediate transmission of these organisms across individual macaques (MacIntosh et al. 2010), and preliminary evidence suggests that infection with at least one of the directly transmitted worms, Oesophagostomum aculeatum, appears to be related to female dominance rank (Hernandez et al. 2009). In this study, we further explore whether social factors are important mediators of nematode parasite transmission among the macaques of Yakushima. Ultimately, investigating relationships between social interactions (networks) and infection potential can highlight the roles that certain individuals, i.e. key hosts or "super spreaders", may play in the long-term transmission dynamics of infectious disease agents. Such information is imperative to any understanding of the mechanisms underlying both host and parasite population processes.
