WIDDER, P. D. *; HUSAK, J.F.; BIDWELL, J.R.; Oklahoma State University, Stillwater; Oklahoma State University, Stillwater; Oklahoma State University, Stillwater: Swim Speed and Cholinesterase Activity in Organophosphate Exposed Anuran Tadpoles

A commonly used biomarker for exposure to organophosphate pesticides is cholinesterase (ChE) activity, however the ecological relevance of this parameter remains largely unexplored in anurans. Combining ChE analyses with behavioral or performance evaluations may assist in understanding the ecological significance of reductions in activity of this enzyme. We examined the effect of three sub-lethal, environmentally relevant exposure levels (0.001, 0.01, and 0.1 mg/l) of a common organophosphate insecticide, chlorpyrifos, on swim speed and cholinesterase activity of Rana sphenocephala (southern leopard frog) and Pseudacris streckeri (Strecker�s chorus frog) tadpoles. Concern over environmental realism of wholly aqueous exposure prompted us to examine how inclusion of pond sediment in test chambers for one species (Rana) influenced responses to the pesticide. ChE activity decreased with increasing dose and was significantly different at the highest dose from controls in all tests (p<0.0001). Swim speed never differed significantly from controls in either species, however tended to not change in the sediment treatment but decrease in non-sediment treatments such that swim speeds were significantly different at the highest dose (p<0.0001). Individual swim speed did not correlate with individual ChE activity. Our results suggest that while ChE activity decreases with dose in tadpoles, the ecologically relevant parameter of swim speed may not be similarly affected. Additionally, our results demonstrate including sediment in contaminant exposures influences tadpole response to chlorpyrifos, an aspect that should be considered in future assessments of this type.