Parasite life cycle evolution and the ecology of trophic interactions

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Many parasites, some of medical and veterinary importance, have complex life cycles, in that they infect one or more intermediate hosts as larvae before they reproduce sexually in a final (definitive) host. Transmission between hosts is often trophic; the current host is eaten by the next host. Incredibly, some parasites infect up to four different hosts before reproducing. Why do parasites have such complex life cycles? This is a puzzling lifestyle, given that at each step in the life cycle, parasites risk not being transmitted to their next host and thus dying before reproducing. This project aims to better understand the evolution of parasite life cycles and has two objectives: 1) to reconstruct how life cycles evolved in the major groups of parasitic worms, and 2) to evaluate life cycle variation in the context of food webs and foraging ecology (i.e. who eats who and how often). These objectives will be addressed by compiling a comprehensive database on parasite life cycles as well as on the position of the parasites hosts in food webs (i.e. their body sizes and trophic levels). The project will lead to a better appreciation of how feeding interactions shape parasite strategies, and it will help to understand the ecological roles of parasites, an important research priority given the rapid pace of contemporary environmental change.