Trematode community structure in the pulmonate snail Physa gyrina.

Trematode community structure was examined in the pulmonate snail Physa gyrina over a 12-mo period. A total of 1,181 snails was collected from Charlie's Pond, North Carolina, and was found to be parasitized by 6 trematode species. Infracommunities were relatively species rich when compared to previous studies, with 18.4% of infected snails having multi-species infections. Halipegus eccentricus was found in 88.4% of multiple infections, usually with 1 of 2 other autogenic, egg-transmitted species (Haematoloechus complexus and Glypthelmins quieta). Neither negative interspecific interactions nor a dominance hierarchy were apparent among the trematodes. These factors, along with high snail vagility and the temporal heterogeneity of infective stages in the environment, are suggested to have contributed to the high number of multiple infections. Halipegus eccentricus was also the most prevalent parasite throughout the study, occurring in nearly 50% of all snails during May, June, and July. Apparent parasite-induced host mortality caused by this trematode species contributed to increasing species diversity in larger snails. The component community was also affected by the continuous recruitment of new snails into the host population and by changes in the number of infective stages present over time.