Behavioural ecology: the impact of parasitism

An overview of the literature in behavioural ecology and parasitology suggests that parasitism is an underestimated determinant of the survival value of behaviour. Behavioural manifestations of infection might arise as host adaptations (defence), parasite adaptations (manipulation) or simply as the result of pathological consequences of infection. The functions (if any) of most behavioural manifestations of infection are unknown. Defence and manipulation are not mutually exclusive, and selective pressures imposed by the parasite and the host on the host's behaviour can act in the same ("coexistence') or different directions ("conflict'). The behavioural manifestations of infection will thus represent the net outcome of the selective pressures acting on each of the two partners. An overview of the examples of host behaviours associated with infection gives the impression that parasite manipulation is most clearly exhibited in intermediate hosts, while behavioural changes associated with infection in definitive hosts seem more closely akin to defence. The broad patterns into which the various examples fall will depend upon factors such as the relative fitness costs of infection, the costs of defence and the costs of manipulation avoidance. Conversely, whether parasites evolve manipulative strategies will depend upon the benefits to be gained and the ease with which novel behaviours (or existing behaviours in novel contexts) can be elicited. -from Authors