Carryover effects of pesticide exposure and pond drying on performance, behavior, and sex ratios in a pool breeding amphibian

Abstract

AbstractNeonicotinoid pesticides are widely used to combat agricultural and forest pests, yet the extent of their biological effects and synergies with other stressors is not well understood, particularly for species with complex life cycles such as amphibians. While there is extensive research on the impacts of agricultural chemicals on amphibians (particularly larval stage), research on the effects of the new class of widely used neonicotinoid pesticides across life stages is lacking. In this study, we used aquatic mesocosm manipulations and terrestrial locomotor and behavior trials to evaluate demographic, behavioral, and fitness carryover effects of sublethal neonicotinoid pesticide (imidacloprid) exposure and hydroperiod length on the wood frog (Rana sylvatica), a model organism. We found that the interaction of imidacloprid exposure and shorter hydroperiod led to decreased larval survival to metamorphosis (0.54 ± 0.14, compared to control 0.75 ± 0.04). When exposed to their thermal optimum (18°C), individuals exposed to imidacloprid as larvae had higher terrestrial locomotor performance (284.08 ± 28.62 body lengths traveled) but also experienced the largest decreases in performance (147.88 ± 19.27 fewer body lengths traveled) after terrestrial imidacloprid exposure. In a 48‐h substrate choice experiment, post‐metamorphic frogs did not show behavioral avoidance of imidacloprid‐treated substrates. Finally, we observed a skewed juvenile sex ratio from imidacloprid treatments (~10% fewer males compared to control), and we were not able to assign 15.7% of individuals from imidacloprid treatments to either sex due to ambiguous reproductive organ morphology. Our empirical assessment of carryover effects of chemical exposure and pond drying provides insights into the physiological capacity of taxa with complex lifecycles to respond to contaminants experienced at multiple life stages and informs best practices for neonicotinoid pesticide use in forest settings and conservation strategies for pond‐breeding amphibians.