Parasitism and behavioural syndromes in the fish Gobiomorphus cotidianus

It is becoming clear that individual animals exhibit behaviours that are repeatable, consistent and predictable across various contexts and time, and that may be correlated to form behavioural syndromes. The influence of parasitism on host behaviour, although well-documented, is only now being examined in a multi-trait context, and behavioural syndromes provide a framework for such investigations. We test the hypothesis that parasites modify host behavioural syndromes by quantifying the relationship between infection by four trematode species and the correlations, repeatability and consistency of three host behaviours (activity, aggression and boldness) in a freshwater fish, Gobiomorphus cotidianus, in the presence and absence of a predator odour. There was a significant correlation between activity and aggression, and both these behaviour showed higher values in the presence of a chemical predator cue. Of the behaviours tested, only aggression responses were significantly related to infection with one of the parasites, Apatemon sp. Activity, aggression and boldness scores were repeatable across test sessions, but much less so in the presence of a predator cue. Interestingly, individual-level consistency in activity and aggression was significantly associated with infection by Telogaster opisthorchis, Deretrema philippae and/or Apatemon sp., with the direction of the association depending on the behaviour tested. These findings suggest that behavioural syndromes may not only be targets for adaptive host manipulation by parasites, but also that, even if through mere pathology, parasites could act as external agents generating variation in behavioural syndromes.