Changes in thermal sensitivity of Rhinella arenarum tadpoles (Anura: Bufonidae) exposed to sublethal concentrations of different pesticide fractions (Lorsban® 75WG)

Abstract

The intensive use of agrochemicals and the rapid increase of global temperatures have modified the thermalconditions of aquatic environments, thus increasing amphibians’ vulnerability to global warming and positioningthem at great risk. Commercial formulations of chlorpyrifos (COM) are the pesticides most widely used inagricultural activities, with a high toxic potential on amphibians. However, little is known about the separateeffects of the active ingredient (CPF) and adjuvants (AD). We studied the thermal sensitivity at different concentrationsand pesticide fractions in Rhinella arenarum tadpoles, on thermal tolerance limits (CTmax = Criticalthermal maximum and CTmin = Critical thermal minimum), swimming speed (Ss), Optimum temperature (Top),and Thermal breadth 50 (B50). Our results demonstrate that the pesticide active ingredient, the adjuvants, andthe commercial formulation of chlorpyrifos differentially impair the thermal sensitivity of R. arenarum tadpoles.The pesticide fractions affected the heat and the cold tolerance (CTmax and CTmin), depending on the concentrationsthey were exposed to. The locomotor performance (Ss, Top, and B50) of tadpoles also varied amongfractions, treatments, and environmental temperatures. In the context of climate change, the outcomes presentedare particularly relevant, as mean temperatures are increasing at unprecedented rates, which suggests thattadpoles inhabiting warming and polluted ponds are currently experiencing deleterious conditions. Consideringthat larval stages of amphibians are the most susceptible to changing environmental conditions and the alarmingpredictions about environmental temperatures in the future, it is likely that the synergism between high temperaturesand pesticide exposure raise the threat of population deletions in the coming years.