Multigenerational effects of glyphosate-based herbicide and emamectin benzoate insecticide on the reproduction and gene expression of the copepod Pseudodiaptomus annandalei (Sewell, 1919).

This study investigates the effects of glyphosate-based herbicide (GLY) and pure emamectin benzoate (EB) insecticide on the brackish copepod Pseudodiaptomus annandalei. The 96h median lethal concentration (96 h LC50) was higher in the GLY exposure (male: 3420.96 ± 394.67 μg/L; female: 3093.46 ± 240.67 μg/L) than in the EB (male: 79.10 ± 7.30 μg/L; female: 6.38 ± 0.72 μg/L). Based on the result of 96h LC50, we further examined the effects of GLY and EB exposures at sub-lethal concentrations on the naupliar production of P. annandalei. Subsequently, a multigenerational experiment was conducted to assess the long-term impact of GLY and EB at concentrations 375 μg/L, and 0.025 μg/L respectively determined by sub-lethal exposure testing. During four consecutive generations, population growth, clutch size, prosome length and width, and sex ratio were measured. The copepods exposed to GLY and EB showed lower population growth but higher clutch size than the control group in most generations. Gene expression analysis indicated that GLY and EB exposures resulted in the downregulation of reproduction-related (vitellogenin) and growth-related (myosin heavy chain) genes, whereas a stress-related gene (heat shock protein 70) was upregulated after multigenerational exposure. The results of the toxicity test after post-multigenerational exposure indicated that the long-term GLY-exposed P. annandalei displayed greater vulnerability towards GLY toxicity compared to newly-exposed individuals. Whereas, the tolerance of EB was significantly higher in the long-term exposed copepod than in newly-exposed individuals. This suggests that P. annandalei might have greater adaptability towards EB toxicity than towards GLY toxicity. This study reports for the first time the impacts of common pesticides on the copepod P. annandalei, which have implications for environmental risk assessment and contributes to a better understanding of copepod physiological responses towards pesticide contaminations.