REPRODUCTIVE STRATEGY OF DAPHNIA-MAGNA AFFECTS THE SENSITIVITY OF ITS PROGENY IN ACUTE TOXICITY TESTS

Maternal nutrition in Daphnia magna affects the body size of the young and the sensitivity of the brood for acute exposure to cadmium, but not to chromium (VI). This phenomenon may contribute to inter-as well as intra-laboratory variation in test results, because Daphnia culture techniques are not yet standardised in a sufficient way. In one set of trials four food ration levels of the green alga Chlorella pyrenoidosa were given to a cohort of adult D. magna. After eight days brood size and the size of young became adapted to the new food ration level. At low levels, small broods were produced which consisted of large neonates, whereas at high food levels many tiny young were born. In acute toxicity tests with cadmium the sensitivity of the neonates appeared to be connected with their body size. The smallest young were three times more sensitive than the largest neonates, comparing the 48-h LC50. No difference in sensitivity occurred during acute exposure to chromium. © 1990.