The effects of pesticide exposure on ultraviolet-B radiation avoidance behavior in tadpoles

Effects of contaminants on behavior may have important consequences on wildlife populations because behaviors such as predation, predator avoidance, reproduction, and social interaction can affect population dynamics. As a common environmental stressor, ultraviolet-B (UVB) radiation causes various deleterious effects and some aquatic organisms actively avoid UVB radiation in water. However, the extent to which environmental contaminants can impair UVB avoidance has not been evaluated, which may cause greater UVB exposure and toxicity. In the present study, we used Xenopus laevis tadpoles to determine if acute exposure to sublethal concentrations of agricultural chemicals can alter tadpole response to UVB radiation. We exposed tadpoles to four pesticides (malathion, endosulfan, α-cypermethrin, and chlorothalonil) for 96 h. At the end of the exposure, tadpoles were transferred to tanks divided into UVB and no-UVB areas. We observed tadpoles for 30 min and recorded time spent in the UVB area. We compared the proportion of time tadpoles spent in the UVB area among different concentrations for each pesticide. There was no significant difference between FETAX control and solvent control tadpoles. When combined, control tadpoles spent less than half of the time in the UVB area indicating that X. laevis tadpoles exhibit UVB avoidance behavior. Tadpoles exposed to 5 μg/L endosulfan spent significantly more time under UVB than control tadpoles. Other pesticides had no effect on tadpole UVB avoidance behavior. Our results suggest that some neurotoxic pesticides can affect UVB avoidance in larval amphibians, which may increase their exposure and subsequently the risk of UVB-induced damage. The present study highlights the importance of examining the interaction between two stressors that co-occur across broad spatial scales and to consider behavioral alteration when evaluating the risk of pesticides to amphibians.