Collective disruption: consequences of parasitism for collective animal behaviour

Highly coordinated animal groups such as schooling fish, migrating birds and swarming insects are ubiquitous in nature, and these complex displays of collective behaviour emerge from local interactions between individuals. Although collective behaviours are known to confer benefits, they also come with the standard costs of group living, including increased risk of parasite infection. Notably, parasites can have profound effects on individual behaviour, which may in turn affect the inter-individual interactions that drive collective behaviour. Thus, given the commonness of parasites in animal populations and their widely appreciated effects on animal hosts, parasitism may be a key force shaping the ecology of collective behaviour. In this article, we use information transfer as a unifying theme to explore how the effects of parasites on individuals translate to the collective, focusing on four common collective behaviours: decision-making, collective movement, synchronization and construction. We also discuss the implications of parasite-altered collective behaviour for processes such as parasite transmission, wildlife conservation and animal culture.