The consequences of parasitic infections for host behavioural correlations and repeatability

The lifecycles of parasites are often complex, with multiple successive hosts. Many parasites have evolved the ability to modify the behaviour of their present host to increase the chance of transmission to the next host. Few studies to date have considered how a suite of related behavioural traits in the host can be affected by parasitic manipulations. The present study investigated the effect of two trematode parasites, Coitocaecum parvum and Microphallus sp., on the behaviour of their amphipod host (Paracalliope fluviatilis) in a behavioural syndrome framework. This framework focused on the correlations between, and repeatabilities within suites of behavioural traits. Three activity-related behavioural tests were conducted: phototaxis (response to light), horizontal activity, and vertical distribution. Infection by C. parvum did not have any significant effect on any of the behavioural traits investigated. However, amphipods infected by Microphallus sp. spent less time in the light. Surprisingly, amphipods harbouring Microphallus sp. also showed stronger behavioural correlations in general, compared to those of uninfected hosts. Furthermore, the repeatability of the phototaxis test for infected amphipods was lower than that of uninfected amphipods. Given these results, we encourage future studies to use this behavioural syndrome framework.