Behavioural impacts of trematodes on their snail host: Species‐specific effects or generalised response?

Abstract

AbstractBehavioural changes induced by parasites are extremely common, but their ultimate causes are often difficult to determine: they may represent adaptive manipulation by the parasite, adaptive responses by the host, or non‐adaptive side‐effects of infection. Contrasting the impacts of different parasites on the same host species offers an opportunity to test for species‐specific changes in host behaviour, which are less likely to be general side‐effects. Here, we tested the impacts of three trematode species (Apatemon sp. I, Plagiorchioid sp. I, and Maritrema poulini) on movement, microhabitat choice and responses to predator cues of their common intermediate host, the freshwater snail Potamopyrgus antipodarum. All three trematodes cause the castration of their host, and thus adaptive host responses to infection can be ruled out. In laboratory trials, snails infected with Apatemon sp. I moved a shorter total distance during the experimental period than uninfected control snails. However, all three trematode species similarly neutralised the attraction to lighted areas shown by uninfected snails, and none of the trematodes affected the time spent moving by their host or its responses to predator cues. Overall, there was little evidence for species‐specific effects on host behaviour by the three different trematode species in the same snail host. The single difference in induced behavioural change, involving one trematode species and one specific behavioural measure, is insufficient to reject the hypothesis that the behavioural impacts on the snail host are general and non‐adaptive by‐products of trematode infection.