Weak effects of chlorpyrifos at environmentally relevant concentrations on fitness-related traits in agile frogs

The widespread application of pesticides makes it important to understand the impacts of these chemicals on wildlife. Chlorpyrifos, an organophosphate insecticide that is still used en masse over large parts of the globe, can affect the development and behavior of non-target organisms and may thereby alter predator-prey interactions. To investigate whether environmentally relevant concentrations of chlorpyrifos affect survival, somatic, cerebral, and sexual development, as well as anti-predator behavior of the agile frog (Rana dalmatina), we exposed tadpoles to one of three treatments (0, 0.5, or 5 μg chlorpyrifos / L) either for three days (acute exposure) or throughout larval development (chronic exposure). We measured mortality, activity, and space use in the presence or absence of chemical cues of predatory fish, brain morphology, length of larval development, body mass at metamorphosis and two months later, and phenotypic sex. Compared to control individuals, tadpoles acutely exposed to 5 μg/L chlorpyrifos showed a shorter freezing response to predator cue on the first observation day. Also, chronic exposure to the same concentration decreased body mass at metamorphosis. Neither the chronically nor the acutely applied 0.5 μg/L chlorpyrifos concentration had any significant effect on the evaluated traits. Our results demonstrate that exposure to chlorpyrifos can induce changes in behavior and may result in lowered body mass of agile frog tadpoles, but only if the insecticide is present chronically at relatively high concentrations. Thus, agile frog tadpoles appear to be relatively tolerant to chlorpyrifos, but may suffer from its repeated high-dose application.