Ashley Darst

The Twin Cities metropolitan region, like many urban environments, has a history of heavy metal pollution from sources such as leaded gasoline and paint, in addition to continued inputs from industry and transportation. Urban metal pollution contributes to elevated childhood blood lead levels and less explored impacts on the urban ecosystem. The Minneapolis-St. Paul Long Term Ecological Research Program seeks to investigate these impacts and to understand why some organisms tolerate exposure to heavy metals better than others. We are testing the hypothesis that evolutionary histories with environmental toxins have pre-adapted certain organisms to anthropogenic pollutants, such as heavy metals. Butterflies are a good system to investigate this question because closely related species vary widely in host plant chemistry, and we can quantify their evolutionary history with mutagenic host plant defensives. We collected 26 species representing independent larval diet shifts from across a gradient of pollution in the Twin Cities, using wing area as a proxy for performance. Wing area decreased with increasing lead concentrations, and this relationship differed between butterfly species. However, differences in tolerance to lead was not associated with host plant mutagenicity. Other factors such as the degree of host plant specialization and the amount of lead uptake by host plants may contribute to differences in species tolerances. Knowing why certain species are better at tolerating pollutants than others will be important as we continue to contaminate the environment.