Left high and dry: The interactions between trematodes and pond drying events in Boulder, Colorado

Elliott, Sophie

Undergraduate Honors Thesis

Left high and dry: The interactions between trematodes and pond drying events in Boulder, Colorado Public Deposited

Analytics

Citations

Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/td96k4048

Abstract

The frequency and intensity of drought conditions in the western United States have increased over the past several decades and are forecasted to worsen in the future. Wetlands and their aquatic inhabitants are highly vulnerable to drought, including the freshwater snails that function as important hosts for trematode parasites. During a survey from 2007-2009, trematode infections in pond snails were found to be rare in Boulder. However, in the summer of 2022, a high prevalence and diversity of trematode infections were detected in aquatic snails in South Boulder. This presented an interesting opportunity to track the populations of these trematode taxa, and their snail hosts, over the course of a drying event to measure how parasites respond to progressive dry downs in ponds. Using a natural experiment, I explored the following questions: a) how does drought impact snail density?, b) how does infection status and living status of snails change with time, and what impact does snail size have on those variables?, and c) how does the overall prevalence of each trematode taxon change with time (in the case of a perennial pond)? I focused on three ponds (two ephemeral that dry out seasonally and one perennial that holds water year round), and carried out biweekly field samples per pond from early September to mid-November 2022. The dissection of nearly 3,000 snails of two species revealed the detection of six trematode taxa. Results indicated that the density of snails decreased significantly over time at the two ephemeral ponds but increased at the perennial pond. Larger snails were disproportionately more likely to die based on the recovery of dead and empty shells at the ephemeral ponds. At the perennial pond, where ~20% of all snails were infected, infection prevalence was greatest among larger snails and showed significant declines through time, although prevalence differed among trematode taxa. This is likely due to a decline in the addition of new infections to ponds over time. These findings help gain insight into how trematodes in Boulder could be impacted by future drought conditions and raise important questions about why infections in 2022 appear to have increased relative to an earlier survey.

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