Ecology and evolution of parasite-host relationships in a real ecosystem

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Parasite infections shape the evolution and ecology of fishes, but we have little understanding of how rapidly changes in parasite levels lead to changes in populations, communities, and ecosystems. Our proposed research project will investigate these questions through collaboration with a 5 million dollar research initiative funded by the National Science Foundation (NSF) of the United States. This NSF project involves experimental manipulations of whole stream ecosystems on the tropical island of Trinidad. In particular, guppies (a small and prolific freshwater fish) will be introduced from streams characterized by high predation and parasitism into formerly guppy-free streams characterized by low predation and parasitism. Very detailed monitoring by the NSF team following this introduction will enable a detailed investigation of the speed of evolutionary change in the guppies and any consequences for interacting species and for the ecosystem. The NSF project focuses entirely on the effects of predation, whereas we will add the parasite dimension. Our study thus examines the ecological and evolutionary consequences of shielding a fish population from one of its major parasites. This is a common strategy in aquaculture and in the conservation of endangered species in Canada, and our results will therefore inform the consequences of these activities. For example, a reduction in parasitism may lead to a rapid loss of resistance to parasites, thus having negative consequences when populations are re-exposed to parasites. The potential relevance to Canadian fishes is particularly likely because the specific ectoparasite under study (Gyrodactylus) is an extremely important pathogen of freshwater and marine fishes in Canada. Our proposed project is novel because no studies have examined the consequences of controlled and replicated experimental manipulations of parasitism in otherwise natural ecosystems. It is timely because the NSF experiments commence this spring and we need to have our sampling team in place as soon as possible.