Effects of a Neonicotinoid Insecticide and Population Density on Behavior and Development of Wood Frogs (Rana sylvatica)

Abstract

Amphibians have been facing global declines over the last decades from direct and indirect effects of anthropogenic activities. A contributor to declines is waterway contamination from agricultural runoffs of pesticides such as neonicotinoids. Beyond direct and indirect effects of the pesticide, few studies have investigated the possible interactions between neonicotinoids and natural environmental stressors across larval development, which could alter the strength and direction of observed neonicotinoid effects. The present study used a fully crossed design to investigate how a concentration of imidacloprid (a neonicotinoid; 10 µg/L) measured in surface waters interacted with low and high population densities (0.33 and 1 tadpole/L, respectively), an important environmental stressor, to influence behavior and development across metamorphosis in wood frogs (Rana sylvatica), known to breed in agricultural landscapes. Behaviors were measured in the absence and presence of predation cues using open‐field tests at three distinct developmental stages, up to the metamorph stage. We found that imidacloprid did not interact with population density or independently affect behaviors in the absence of predation cues. However, individuals raised at high density compared with low density were more active at an early developmental stage but less active at metamorphic climax. Furthermore, both density and imidacloprid independently decreased the natural freezing response of tadpoles to predation cues. Finally, we found that distance traveled in the open‐field test was weakly repeatable between aquatic stages but not repeatable across metamorphosis, a pattern that was not affected by treatments. The present study provides novel insights on the ecotoxicology of imidacloprid in the presence of a natural stressor, highlighting the importance of including behavioral assays and natural stressors in studies of amphibian ecotoxicology. Environ Toxicol Chem 2022;41:2968–2980. © 2022 SETAC

Connecting the Pipes: Agricultural Tile Drains and Elevated Imidacloprid Brain Concentrations in Juvenile Northern Leopard Frogs (Rana pipiens)

“…Neonicotinoids are known to have detrimental effects on aquatic, emergent, and terrestrial invertebrate communities, which serve as prey for metamorphs and adult amphibians. ,− It is plausible that decreased food consumption could lead to differences in brain size; however, Woodley et al did not find differences in brain size among northern leopard frog tadpoles raised under reduced food availability compared to the control. Furthermore, high density is known to cause smaller body mass at metamorphosis; − however, we did not detect differences in body mass between wetland types during this study. Given the findings of previous studies in conjunction with the results from the present study, we suggest that changes in cerebellum size in juvenile northern leopard frogs are likely a result of exposure to contaminants in the field.…”