Comparative toxicant sensitivity of sexual and asexual reproduction in the rotifer Brachionus calyciflorus

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Abstract
Cyclically parthenogenetic zooplankters like rotifers are important tools for assessing toxicity in aquatic environments Sexual reproduction is an essential component of rotifer life cycles, but current toxicity tests utilize only asexual reproduction We compared the effects of four toxicants on asexual and sexual reproduction of the rotifer Brachionus calyciflorus Toxicants had a differential effect on sexual and asexual reproduction, with sexual reproduction consistently the most sensitive Concentrations of 0 2 μg/ml PCP (sodium pentachlorophenate) had no effect on the asexual reproductive rate, but significantly reduced sexual reproduction Likewise, chlorpyrifos concentrations of 0 3 μg/ml had no significant effect on asexual reproduction, but sexual reproduction was significantly reduced There was no difference in NOECs, LOECs, and chronic values for asexual and sexual reproduction for cadmium and naphthol tests However, comparison of toxicant effect levels revealed that sexual reproduction was more strongly reduced at each toxicant concentration The four toxicants tested inhibited sexual reproduction 2 to 68 times more than asexual reproduction at the lowest observed effect concentrations Toxicants inhibited sexual reproduction in its initial step sexual female production Because sexual reproduction is more sensitive, toxicity tests based exclusively on asexual reproduction may not be protective of rotifer life cycles