Predators alter host-parasite interactions via trait-mediated indirect effects

Predators directly interact with their prey. These direct interactions can indirectly alter the interactions between prey and other community members. For example, predators can alter prey life history, behavior, or morphology resulting in an indirect change in the interaction between their prey and another species (Trait-mediated indirect effects). We used two dominant predators of the zooplankter Daphnia, Bluegill sunfish (Lepomis macrochirus) and larvae of the phantom midge fly Chaoborus punctipennis, to observe how predator presence altered Daphnia traits. These trait changes were predicted to influence the interaction between Daphnia and Metschnikowia bicuspidata, a virulent and common (>40% prevalence in some lakes) fungal endo-parasitoid. In a series of susceptibility and life history assays, we determined that predators altered prey susceptibility in a genotype specific manner, they influenced parasite fitness, and affected prey life history. All of these effects have important implications in disease dynamics. This study highlights the importance of predator-induced trait-mediated indirect effects on host-parasite interactions and more generally of examining species interactions in the context of the community in which they occur