Parasite-induced behavioural changes to the trade-off between foraging and predator evasion in a marine snail

Abstract

Trophic interactions in ecological communities not only affect consumer-resource densities, but also induce phenotypic responses that can ripple through a food web to influence prey resources, competitors and other predators (i.e. trait-mediated interactions). Predators affect short-term trade-off decisions in prey species through behavioural alterations, yet the role of parasites in the context of trait-mediated interactions is rarely discussed, despite our extensive knowledge of parasite-induced behavioural alterations. Adding parasites to the picture, the foraging–predation trade-off presents an interesting case where the effects of predator- and parasite-induced behavioural responses occur in conjunction. Empirical studies on the effect of parasites on trait-mediated anti-predator responses are still scarce, especially in marine systems. Our experiments used marine mud snails, Zeacumantus subcarinatus (Batillariidae), infected with the trematode parasites Maritrema novaezealandensis and Philophthalmus sp. to investigate the effects of trematode-induced behavioural alterations on the trade-off between food acquisition and predator avoidance in the presence of a range of predation cues. We found that the time taken to initiate anti-predator responses was overall significantly shorter in M. novaezealandensis-infected snails than in uninfected snails, while it was significantly longer for Philophthalmus-infected snails. In the simultaneous presence of odours from an injured conspecific and a crab predator, however, the reaction time between uninfected and M. novaezealandensis-infected snails did not differ while Philophthalmus-infected snails were still markedly slower than the former groups. Our results demonstrate species-specific parasite-induced behavioural changes in the presence of imminent predation risk. However, effects of the trematodes on overall feeding and fleeing times were not detected in our experiments; thus, the net effect of parasitism on the foraging–predation trade-off remains unknown.