Clonal variation in acetylcholinesterase biomarkers and life history traits following OP exposure in Daphnia magna.

Two clones of Daphnia magna (Standard and Ruth) were exposed for 7 days to sub-lethal concentrations of acephate (5.0 and 10.0 mg/L). Survivorship, individual growth, reproduction and the population growth rate (lambda) were evaluated over three weeks. Acetylcholinesterase (AChE) activity was measured on days 2, 7 and 21. Acephate exposure inhibited AChE activity but had no direct effect on life history (LH) traits. There was also no effect of clone on AChE activity, LH and lambda. However, a significant interaction between clone and acephate concentration was found on both fecundity and lambda. AChE inhibition at 48 h was associated with a decrease in lambda in the Standard clone and an increase in lambda in clone Ruth. Therefore, our findings show that genotypic variation will influence the link between AChE activity and toxic effects at higher levels of biological organisation in D. magna.