Metabolic switch explains the sublethal effects induced by glyphosate-based herbicide in tadpoles of a farmland frog Microhyla fissipes

The sublethal effects of a practically nontoxic GBH (KISSUN®) were investigated in tadpoles of M. fissipes, a farmland inhabiting amphibian. GBH exposure caused higher temperature preference, growth suppression, shorter and weaker tails in these tadpoles. These sublethal effects would likely affect the environmental adaptation ability, locomotor activity, competitive capacity and survival rate of tadpoles and thus might have profound influence on their population dynamics. Higher temperature preference might be an adaptive strategy for improving the efficiency of damage repair system activated by GBH exposure, as well as compensating for the reduced locomotor activity and sustaining energy metabolism. Growth suppression and tail morphological change were associated with reduced intensity of overall protein synthesis and structural protein synthesis, especially muscle specific genes. Transcriptional analysis suggested that GBH-treated tadpoles had suppressed carbohydrate and lipid catabolism, while encouraged amino acid catabolism. We speculated that metabolic switch to amino acid might be an adaptive strategy for compensating the reduced contribution of carbohydrate and lipid in energy production, and it provide a metabolic explanation for the downregulation of protein synthesis, growth synthesis and morphological change. Our results systemically revealed the molecular processes underlying the sublethal effects in an amphibian caused by GBH. It suggested that metabolic switch might be a consensus toxicologic mechanism of growth suppression across fish and amphibians. GBH exposure were carried out in plastic containers (29 cm×19.5 cm×7 cm) with 1000 mL water at 24 ± 0.5°C (L : D = 12 : 12). Tadpoles were randomly assigned to 0 mg/L (control), 60 mg/L, 90 mg/L, and 120 mg/L GBH exposure groups (5 replicates/containers for each treatment group; 20 tadpoles in each replicate). GBH exposure lasted for 10 days, and survival rates were recorded daily. Firstly, observe the distribution of tadpoles in plastic containers and measure the morphological traits of tadpoles. Next, Paraffin section and H&E staining were performed to explore the histopathological response of tadpoles. Thirdly, Comparative transcriptomics was conducted to analyze the underlying mechanisms between control, 60 mg/L and 90mg/L GBH exposure group.