WIDDER, P. D. *; BIDWELL, J.R.; Oklahoma State University, Stillwater: Performance and Predation Evaluations of Pesticide Exposed Rana sphenocephala

Small wetlands embedded throughout modern agricultural landscapes provide important breeding habitat for many amphibians. However, these habitats receive inadvertent doses of agricultural chemicals, including organophosphate pesticides (OPs), due to run-off, overspray, and/or atmospheric deposition. A commonly used biomarker for exposure to OPs is cholinesterase (ChE) activity and recent studies have correlated reductions in this essential neurological enzyme with declines in amphibian populations. However, the ecological mechanisms that tie amphibian population declines to ChE activity reductions have not been specifically investigated. Combining ChE analyses with behavioral or performance evaluations may assist in understanding the significance of reductions in its activity. We examined the effect of four sub-lethal exposure levels (1, 10, 100, 200 μg/L) of a common OP, chlorpyrifos, on ChE activity and evaluated swim speed performance in Rana sphenocephala tadpoles. We also examined how including pond sediment in test chambers influenced responses to the pesticide. Finally, we examined how chlorpyrifos dose influenced odonate predation rates in both laboratory and mesocosm trials. We found tadpole swim speed unaffected by dose despite reductions in ChE greater than 50% in the highest three doses, but qualitative changes to swimming behavior were evident when pond sediment was not present. There were no differences in tadpole survival in laboratory predation trials. However, mesocosm predator trials resulted in high predator mortality, and subsequently higher tadpole survival rates in exposed ponds. This greater sensitivity to chlorpyrifos in odonate predators suggests reductions in tadpole ChE will not result in an increase in invertebrate predation.