Humans have caused major changes to our environment, one example being pesticide pollution. Over 1 billion pounds of pesticides are used annually in the United States. Pesticides do not remain isolated in the terrestrial environment but accumulate in freshwater systems. Globally, parasite-induced diseases are on the rise and pesticide pollution may be a contributing factor. Echinostoma trivolvis, a prominent trematode parasite in SW Ohio, requires Ramshorn snails (Helisoma trivolvis) as an intermediate host in their complex life cycle. We investigated the impacts of pesticide exposure on E. trivolvis infected-Ramshorn snails. We hypothesized that snails would be negatively impacted by parasites, pesticides, and their combined effect. We predicted that survival, reproduction, and growth would decrease when subjects were exposed to either parasites, pesticides, or both. To conduct our experiment, snails were collected from the Ecological Research Center, evaluated for infection status, and exposed to their treatment in the lab for 41-days. We recorded mortality, the number of egg masses laid, and mass change for each of the 150 subjects. We found that chronic pesticide exposure by atrazine (p=0.014), carbaryl (p=0.050), and malathion (p<0.001) significantly decreased survival in Ramshorn snails. We also found that infection by parasites stopped Ramshorn egg-laying completely, significantly decreasing reproduction (p<0.001). There were no interactive effects between parasite and pesticide exposure on snail response. Our findings suggest that Ramshorn populations may decline due pesticide-induced mortality. Since Ramshorn snails are important intermediate hosts for many trematode species, pesticide pollution may decrease parasite load in freshwater systems. This indicates that anthropogenic stressors (pesticides) have the potential to disrupt naturally occurring parasite systems. However, this study only encompasses a small part of parasite dynamics in ecosystems, so further research must be explored. This experiment developed my practical research skills, which will be advantageous when I attend graduate school after graduation.
Authors: Emma Svatos
Advisors: Michelle Boone and Miranda Strasburg, Department of Biology
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