By Morgan Hicok

Faculty Mentor: Dr. Abbie Tomba

Abstract

Trematodes are parasitic flatworms that infect freshwater snails and can cause changes in metabolic function and growth. Flow rates and water levels are now more variable due to climate change, increasing stress and dislodgment in the snail population. This study investigates parasitic induced changes in shell morphology and the effect they may have on resistance to changing flow rates. To examine differing flow environments, Elimia populations in two different rivers were sampled for differences in parasitism, shell morphology, and ability to withstand high flow environments. Sample sites at the Potomac River were tidal with low flow, while sites at the Rappahannock River were higher flow with pools and riffles. Snails from both sites were randomly sampled and preserved in 95% ethanol. Approximately 10 random subsamples were taken per sample location. Snails were dissected and measured for shell morphological features, looking specifically at width and aperture (size of shell opening). Shell width, shell aperture, and shell thickness in the Potomac was significantly larger than in the Rappahannock (Kruskal-Wallis p<0.0001). Shell widths and apertures were both significantly larger in infected snails than non-infected snails (Krusal-Wallis p<0.0001). Prevalence of parasitism did not differ between rivers (Χ2 p=0.51). To measure snails' response to high flow, approximately 300 snails were collected per sample location and were subjected to a high flow environment (0.75 m/s) for 10 minutes to determine time of dislodgment. Excluding un-dislodged snails, the Potomac snails were able to hold on for longer than Rappahannock snails in the high flow treatment (Wilcoxon p=0.001). There were no significant differences between parasite groups in ability to maintain traction in high flow (Wilcoxon p=0.39). Infected Elimia in both populations have larger shell widths and apertures, this increase in size does not influence the snail’s ability to resist dislodgment in high flow.