Linking Ecology, Physiology and Human Land Use: The Impact of Environmental Stress on Disease Susceptibility in Larval Amphibians

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Understanding the role that infectious diseases play in natural communities is a key question in community ecology. Host-pathogen interactions, perhaps more so than other types of interactions (e.g. predator-prey & competition), are largely determined by the physiological condition of the host. To gain a predictive understanding of the impact that infection may have on host population dynamics requires a detailed understanding of host physiology and immunology. Freshwater wetlands are primary habitat for snails serving as intermediate hosts for a variety of helminthic parasites including digenetic trematodes. Trematodes are responsible for hundreds of thousands of cases of human disease each year (e.g., schistosomiasis) and have been linked with developmental abnormalities in amphibians. Amphibian deformities, in particular those related to limb development, have now been reported throughout North America. The widespread nature and apparent increase in the prevalence of deformities has lead to substantial interest from scientists and the general public. While preliminary laboratory experiments suggest that infection by trematodes can cause some deformities, researchers have pointed out that there is a need for more fieldwork to evaluate the association in nature. In addition, some research has suggested that land use changes in wetlands, such as increased eutrophication and altered hydrology, may precipitate outbreaks of deformities by increasing abundance of intermediate hosts (snails). We propose to examine the role of the host's hormonal response to land use changes (environmental stress) in terms of how it can regulate disease susceptibility. The proposed project will complement an ongoing study examining how land use changes affect snail (intermediate host) abundance and therefore influence amphibian infection rates. This proposal will add significantly to our knowledge of how free-living animals respond physiologically to anthropogenic land use changes, and the data generated on host susceptibility will add significantly to the development of a predictive model for disease outbreak in this host/parasite system.