Maternal nutritional state determines the sensitivity of Daphnia magna offspring to Fenvalerate pulse exposure.

Abstract
Daphnia populations in the field suffer periodic natural stress conditions such as low food levels. It is known that at low nutritional supply, Daphnia produces fewer but larger offspring, which are acutely less sensitive to chemical stress. We hypothesized that the change in the reproductive strategy may also alter the chronic sensitivity of offspring to pesticides, which usually occur in the field in a pulsed manner. We therefore investigated the influence of maternal food quantity of Daphnia magna on (1) offspring size and successive performance and (2) sensitivity to a 24-h exposure to the pyrethroid insecticide Fenvalerate. Daphnia cultures were maintained at a high and low food level. Produced offspring were subsequently used in life-table response experiments, which were performed under low food conditions. Results showed that low maternal food conditions (compared to high) increased the offspring size at time of birth, reduced age at first reproduction and increased reproductive output, which jointly enhanced offspring fitness as estimated by the population growth rate (r). Fenvalerate exposure in combination with low maternal food levels caused (compared to high) a strong decrease in acute sensitivity of neonates, which was generally also observed for chronic endpoints. Hence, reduction in population growth rate resulting from short-term pesticide exposure appeared to be less strong when compared to daphnids originating from high fed mothers. Our findings illustrate the importance of considering more environmentally relevant conditions (i.e. low maternal food level, short-term exposure) when linking effects observed in laboratory tests to potential risks in the field.

Keywords: Short-term Fenvalerate exposure; Daphnia magna; Food quantity; Maternal effects; Sensitivity; Extrapolation