Lauren Elizabeth Nadler , Jolle W Jolles, Sandra Ann Binning, Jeremy De Bonville, Paolo Domenici, Shaun S Killen, Matthew Silk 

Animals form social groups to gain benefits to numerous fitness-enhancing processes, such as foraging, defense, and energy expenditure. While social grouping can increase parasite exposure, it can also serve as a defensive mechanism against parasites (defined broadly here as organisms with obligate, persistent, and harmful consumer associations with a host). Here, we present a conceptual framework that explores how host sociability affects parasite infection risk in the context of parasite life history, arguing that the positive or negative impact of a social lifestyle on infection risk is strongly linked to the parasite’s transmission mode. This framework focuses on common, non-mutually exclusive differences in parasite transmission: direct vs. indirect, density- vs. frequency-dependent, and simple vs. complex life cycles. We then use this framework to discuss the mechanisms for active parasite avoidance, passive effects of infection-induced phenotypes, and their impacts on host social networks, as well as the additional factors that can modulate these dynamics (e.g., parasite virulence, infection intensity, co-infection by multiple parasites, and environmental factors). The goal of this broad, comparative approach is to provide researchers from multiple disciplines with a unified framework to better understand the relationship between social grouping and host-parasite interactions across diverse systems.