Date of Award

Spring 5-9-2023

Document Type

Honors Thesis



First Advisor

Jacob Kerby, Ph.D.

Second Advisor

Jeff Wesner, Ph.D.

Third Advisor

David Swanson, Ph.D.


selenium, false map turtles, zebra mussels, bioaccumulation, Missouri River

Subject Categories

Biology | Terrestrial and Aquatic Ecology


Metals and metalloids are becoming more prevalent in lakes and reservoirs of South Dakota which are toxic and hazardous in high concentrations or when biomagnified through trophic levels. Selenium is of particular concern as it can bind into the structures of proteins in place of other elements, changing protein structure and function within affected organisms. Zebra mussels (Dreissena polymorpha) are an invasive filter-feeding metal-bioaccumulating species that are rapidly spreading upstream through the Missouri River. They can take up selenium and directly transfer it to higher trophic level taxa. False map turtles (Graptemys pseudogeographica) are a common predator of zebra mussels and serve as a model organism to detect selenium levels in higher trophic level organisms. It was predicted that there would be a higher selenoprotein content in turtles residing in downstream vs upstream reservoirs of the Missouri River due the prevalence of zebra mussels downstream that may contribute to dietary selenium intake. To test this hypothesis, false map turtles were randomly sampled from Lake Francis Case (upstream) and the 59 Mile Stretch of the Missouri River (downstream). Blood samples were randomly selected from both sites and tested for selenoprotein concentration using an ELISA assay. Based on a Bayesian statistical model, there is a 96.3% probability that Lake Francis Case absorbance values are higher than the 59 Mile Stretch absorbance values. Higher absorbance values are indicative of higher concentrations of selenoprotein. These results suggest that the turtles of the 59 Mile Stretch are exposed to lower levels of selenium than those of Lake Francis Case. This indicates that there are other factors to consider. More work must be done to understand the reason for variance in selenoprotein absorbance values between sites and what impact the invasive zebra mussels truly have on other marine inhabitants.



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