Variation in Pesticide Sensitivity Among Resurrected Daphnia pulicaria Genotypes from Hill Lake, MN

Abstract

Previous research on South Center Lake, a eutrophic lake in Minnesota, has shown that ancestral genotypes are more sensitive to a novel contaminant (chlorpyrifos) than contemporary genotypes. It was suggested that the eutrophication history of South Center Lake could have indirectly caused a shift in sensitivity over time. To further investigate this hypothesis, we examined Daphnia genotypes originating from a mesotrophic lake in Minnesota (Hill Lake). The genotypes were hatched from dormant eggs that were laid between 1984 and 2010 A.D., which we divided into two age classes: 1984-1997 A.D. (n=3) and 1997-2010 A.D. (n=6). The genotypes were exposed to chlorpyrifos during 48-hour toxicity tests. Sensitivity, measured as the median effect concentration (EC50), was not significantly different between age classes. This lack of a trend could be explained by the lake’s trophic status (mesotrophic vs. eutrophic). Further testing of Daphnia from Hill Lake could shed light on the influence of eutrophication on contaminant sensitivity.