Asymmetric effects of avermectin insecticides on testicular morphology and function in Bufo gargarizans

Avermectins (AVMs) are widely used insecticides that pose potential risks to non-target organisms through environmental exposure. However, their effects on amphibian reproductive systems remain poorly understood. This study conducted a 14-day exposure experiment on the Asiatic toads (Bufo gargarizans) through food (0.36 ng/d), water (0.02 μg/L), and combined treatments to investigate the asymmetric toxic effects of AVM on testicular morphology and function in this species. Results showed that AVM exposure significantly reduced sperm motility and induced histopathological damage in testes, with the strongest toxicity observed in the combined exposure group. Physiological and biochemical analyses revealed oxidative stress and glycolipid metabolic disorders in the testes of AVM-exposed toads, with the left testis exhibiting more severe oxidative damage, glucose accumulation, and weakened antioxidant capacity compared to the right. Transcriptome analysis further demonstrated distinct gene expression patterns between left and right testes: the left testis exhibited more differentially expressed genes (DEGs) that were enriched in amino acid metabolism pathways, while the right testis exhibited adaptive responses through downregulation of the gluconeogenesis gene PCK1 and upregulation of the antioxidant gene SOD2, enhancing ATP production and antioxidant defense. These findings indicate that AVM induces asymmetric testicular dysfunction in Asiatic toads through oxidative stress and metabolic reprogramming, providing new insights into pesticide ecological risk assessment and amphibian conservation strategies.