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.
2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.