Impact of a microphallid trematode on the behaviour and survival of its isopod intermediate host: phylogenetic inheritance?

The extent to which the ability of parasites to alter host behaviour is phylogenetically inherited as opposed to independently evolved has received little attention. We investigated the impact of an undescribed species of Microphallus on the behaviour and survival of its host, the freshwater isopod Austridotea annectens, to determine if it produced effects comparable to those induced by other trematodes of this genus. There was no difference between the vertical distribution and responses to light of infected isopods and those of uninfected isopods. In contrast, we found that infected isopods were more active swimmers than uninfected isopods, and that they failed to show the evasive responses shown by uninfected isopods when exposed to a simulated predator. There was no detectable effect of Microphallus infection on isopod survival, however. Overall, our results provide no strong evidence that the behavioural manipulation shown by our Microphallus species and that displayed by the well-studied Microphallus papillorobustus are inherited from a common ancestor rather than independently derived.