VINCIE, M.*; BELDEN, L.K.; Randolph-Macon Woman’s College; Virgnia Tech: Does the distance between intermediate hosts alter parasite transmission? A test using free-swimming trematode cercariae and tadpoles

Digenetic trematodes are common parasites in freshwater systems and many species are economically and medically important. These parasites generally require two intermediate hosts to complete their life cycle, with reproduction occurring in the definitive host. Usually the first intermediate host in the parasite�s life cycle is a gastropod, while the second intermediate host is typically another mollusk, a fish or an amphibian. Though much is known about the life cycle of this parasite, little has been found on the distance between a parasite and its intermediate host and the effects this has on infection in the host. We are studying the digenetic trematode Echinostoma trivolvis in an attempt to understand the environmental factors that can regulate infection in host snails and tadpoles. In this study, we examined how proximity to trematode cercariae, the free-swimming life stage that infects second intermediate hosts, impacts infection levels in tadpoles. To do this, we constructed three rectangular tanks and placed cercariae collected from naturally infected Helisoma trivolvis snails in one end and three grey tree frog, Hyla versicolor, tadpoles in fiberglass mesh sections at discreet intervals from the cercariae. We hypothesized that tadpoles closest to the cercariae would be most readily infected. Interestingly, we found the opposite result, that the tadpoles farthest away from the source of cercariae had significantly higher infection levels than those closest to the source of cercariae. Our results could have implications for understanding habitat use by tadpoles in environments where infected snails are present.