Reproductive strategy of Daphnia magna and toxicity of organic compounds

Abstract

Five groups of Daphnia magna were cultured up to the 11th brood on five graded food levels comprised between 0.6 × 10 5 and 5 × 10 5 cells/ml/day of both Selenastrum capricornutum and Saccharomyces cerevisiae and fed with equal amounts. Reproduction, adult body length, weight and age at first brood production were markedly affected by food rations. Minor or no effects were observed on neonate length and weight, though a negative relationship between neonate length and parental food ration was verified. In addition, it was observed that brood to brood oscillations of neonate weight and length are inversely related to the oscillations of mean brood size. Neonates from the last five broods were acutely tested for their sensitivity to two organic compounds of increasing lipophilicity, i.e. ethylbenzene ( K ow = 3.15) and n-butylbenzene ( K ow = 4.05). Toxicity test results at 48 h of exposure revealed only minor effects of feeding levels which could not be explained either by neonate weights or lengths which were measured for the broods tested. Present results show that reproductive strategy, i.e. the inverse relationship between brood size and neonate parameters, should be regarded as generic potential which can be activated to a variable extent and is also effective at constant food condition in the sequence of brood to brood variations.