The objectives of the proposed research are 1) to investigate the impact of mermithid parasitism on depression of mayfly host population size, 2) to investigate the ecological effect and the possible source of parasite induced behavioral alterations of larval host behavior, and 3) to test that behavioral alterations are caused by, rather than correlated with, parasitic infection. Proposed methodology includes: 1) extensive field sampling to estimate mermithid prevalence combined with predictive mathematical models; 2) microcosm experiments to a) quantify ecological effects of parasite induced behavioral alterations on larval mayfly vulnerability to predation from stoneflies and trout, b) infer possible role of host nutritional stress and physical obstruction of host internal function by parasite in producing the behavioral alterations; and 3) the development of a laboratory culture to control and monitor parasite development in the larval host. The key contributions of this research will be 1) an understanding of immediate and long term consequences to host fitness of parasite infections and 2) a consideration of the evolutionary source of behavioral alterations, the importance of side effects of the infection as mediators of the alterations, and the possible constraints acting on the evolution of parasite induced behavioral alterations.
