| The study of parasites and disease in ecological systems is becoming increasingly urgent as diseases emerge at unprecedented rates. Anthropogenic change is a potential driver of the recent acceleration in disease emergence Amphibians are currently undergoing global declines, and habitat alteration and disease are two main causes. Echinostome parasites that infect amphibians in North America have been associated with human development. I explored the impact of echinostomes on amphibians and the mechanisms underlying increased echinostome infection in amphibians in wetlands associated with human development.;First, I used laboratory experiments to examine the impact of echinostome infection on green frog (Rana clamitans) tadpole growth, development and mortality. I found that echinostomes cause high rates of mortality in green frog tadpoles at early developmental stages. Histological analysis revealed that echinostomes disrupt the glomeruli, the main filtration units of the kidney. As tadpoles grow and develop they gain the ability to expel or destroy echinostome cysts post-infection. This ability to eliminate echinostome cysts may protect older tadpoles from the adverse effects of echinostomes.;Next, I utilized field studies to explore the mechanisms underlying elevated echinostome infection abundance and prevalence in amphibians in wetlands associated with human development in northeastern Connecticut. In field enclosure experiments, I found that human development surrounding wetlands did not affect the ability of green frog tadpoles to respond to echinostome infection. These represent the first field experiments to examine the impact of echinostomes on amphibians. Echinostome infection caused high rates of tadpole mortality, similar to levels observed in predation experiments, suggesting that echinostomes could impact tadpole populations. In a second set of field experiments, human development surrounding wetlands did not impact the susceptibility of either gray tree frogs (Hyla versicolor) or green frogs to echinostome infection. Instead, increased echinostome infection prevalence and intensity in amphibians in developed wetlands is more likely driven by changes in the density of snail and bird hosts involved in parasite transmission. Together, these studies show that the impact of echinostomes on tadpoles is determined by factors that operate on a range of scales from cellular through the level of the ecological community. |
