Effects of chlorpyrifos on early development and anti-predator behavior of agile frogs

The widespread application of pesticides makes it important to understand the impacts of these chemicals on wildlife populations. Chlorpyrifos is an organophosphate insecticide which can affect the development and behavior of aquatic organisms and may thereby alter predator-prey interactions. To investigate how environmentally relevant, sublethal concentrations of chlorpyrifos affect anti-predator behavior and larval development of the agile frog (Rana dalmatina), we exposed tadpoles to one of three concentrations (0, 0.5 and 5 μg chlorpyrifos / L) either for a brief period of three days (acute exposure) or throughout larval development (chronic exposure). We observed tadpole activity and space use in the presence or absence of chemical cues of predatory fish. We also assessed mortality, time to metamorphosis, mass at metamorphosis, brain morphology and sex ratio. We found that tadpoles chronically exposed to 5 μg/L chlorpyrifos swam distances that were longer by more than 20 % and exhibited body masses at metamorphosis that were lower by ca. 7 % than in control individuals, but the other fitness-related traits remained unaffected. The lower concentration of chlorpyrifos applied chronically, and either one of the acute chlorpyrifos treatments did not influence any measured trait. Our results demonstrate that exposure to chlorpyrifos can induce changes in locomotor activity and may result in lowered body mass of agile frog tadpoles, but only if the insecticide is present chronically at concentrations which are rarely reached in natural waterbodies. Thus, agile frog tadpoles appear to be relatively tolerant to chlorpyrifos, but may nonetheless suffer from its presence in situations of repeated high-dose application.