Tadpole size, cholinesterase activity, and swim speed in four frog species after exposure to sub-lethal concentrations of chlorpyrifos.

While physiological biomarkers exist to verify exposure of amphibians in natural populations to agricultural chemicals, the ecological relevance of changes in these parameters is often difficult to determine. We compare the relationship between tadpole cholinesterase (ChE; a common enzymatic biomarker of exposure to OP pesticides) and measures of size and swim speed in four native North American species of anurans (Hyla chrysoscelis, Rana sphenocephala, Acris crepitans, and Gastrophryne olivacea). We used four environmentally realistic levels (1, 10, 100 and 200microg/l) of a commonly used organophosphate pesticide (OP), chlorpyrifos, and examined tadpole response at the conclusion of 4 days of exposure. We further examined if the presence or absence of pond sediment influenced tadpole responses, and, in two species, we determined how a 12-day exposure influenced responses. We found species-specific differences in response to the pesticide, with H. chrsysoscelis and G. olivacea being most sensitive; however, the levels of inhibition of ChE activity were generally not sufficient to exert an effect on swim speed as we measured it. Generally, tadpole mass was reduced 20-35% in the highest concentration after 4 days of exposure. We found the presence of sediment to influence these responses, although the effects were not consistent among species. Given these differences in ecologically relevant responses, we recommend exercising caution when making generalizations across different anuran amphibian taxa regarding responses to pesticide exposure.