Animal behaviour meets microbial ecology

Microbial ecologists strive to understand the factors that influence the structures and functions of microbial communities. At first glance, understanding these communities might not seem to offer much to biologists studying the behaviour of animals. However, several exciting new studies demonstrate that microbial ecology has the potential to advance research on both proximate and ultimate questions in animal behaviour. Here we review three such questions: (1) how do animals recognize individuals, group members and kin, (2) how do animals choose among potential mates, and (3) what are the evolutionary costs and benefits of social relationships? Contributions to these problems from microbial ecology come from two basic ideas. First, the structure of animals’ bacterial communities is shaped by their hosts’ environments, physiologies, genotypes and social relationships. In turn, these communities can communicate this information about their animal hosts, especially through odour. Second, social relationships can mediate exposure and susceptibility to bacteria, and this socially mediated transmission can influence the evolutionary costs and benefits of social relationships. Throughout our review, we focus on the bacterial communities of vertebrates because their behaviourally relevant symbionts have received little attention compared to those of invertebrates. We focus on how new genetic tools in microbial ecology make it possible to test long-standing hypotheses in behavioural ecology, and we highlight future research directions at the interface of microbial and behavioural ecology.