By Kate Green

Faculty Mentor: Dr. Abbie Tomba

Abstract

The differential impacts of parasitism on male and female freshwater snails by trematodes, a flatworm, is largely unstudied. While trematode diversity indicates the health of aquatic ecosystems, they have a negative impact on snails by sterilizing them. Snails are vital in aquatic ecosystems; they are an important food source, and their role as dominant grazers of detritus and algae improves water quality. To better understand interactions between snails and trematodes, it is necessary to examine how effects of parasitism differ between sexes, as well as the differences in shell morphology and habitat distribution in both parasitized and non-parasitized snails. In this study, snails of species Elimia virginica were collected from the Rappahannock and Potomac rivers; these distinct populations were sampled randomly within 10-15 square-foot quadrats per sampling location, where flow, depth, and substrate size were measured, as well as non-randomly. All were dissected, with the aperture width, length, shell thickness, and shell width measured with digital calipers and the program ImageJ. Sex and parasitism were determined. Parasitized snails were preserved, with the number and size of parasites quantified. It was determined that parasitized female snails were the largest demographic, with the exception of in shell thickness (p < 0.001). Snails with a larger shell width and aperture length were also indicated to have a greater number of parasites (p = 0.004, p < 0.001), but there was no relationship between the number of parasites and sex (p = 0.932). Rates of parasitism were highly variable between the summer and fall months, with a 10.36% parasitism rate in the summer, and a 4.26% parasitism rate in the fall. While there was a significant difference in the proportions of males vs females parasitized in the summer, they were equally parasitized in the fall (p = 0.007, p = 1). The density of snails in a quadrat was negatively correlated with percent parasitized (p = 0.003, r = -0.76), but positively correlated with percent males (p = 0.004, r = 0.37).