PW12 Pesticide II
Exhibit Hall
8:00 AM - Wednesday
(PW217) Development of a screening method for endocrine disruptors in crustaceans using Daphnia magna (Crusacea, Cladocera).
Tatarazako, N1, 2, Oda, S1, Abe, R1, Morita, M1, Iguchi, T2, 3, 1 National Institute for Environmental Studies, Japan, Tsukuba, Ibaraki, Japan2 CREST, Japan, Kawaguchi, Saitama, Japan3 Okazaki National Research Institute, Okazaki, Aichi, Japan
ABSTRACT- Experiments were conducted to investigate the period of sex differentiation in small cladoceran (Daphnia magna) neonates. Gravid female were exposed to a juvenile hormone-mimicking insecticide, fenoxycarb, which have been found to induce daphnids to develop into male neonates in the previous studies. The stage when eggs are in the ovary prior to the release into the brood chamber was estimated as the period susceptible to the juvenile hormone (JH) analog. Effects of JH analog exposure on daphnids both change in the offspring sex ratio and number of neonates, disappeared immediately after the end of the exposure. This result suggests that the male neonates are induced by the JH analog through the disruption in the endocrine system. Twenty-one-day reproduction experiments revealed that the development into males was not induced by the selected endocrine disruptors for vertebrates, bisphenol A, nonylphenol, and octylphenol, at concentrations that caused reduction in the reproduction rate. A 20-Hydroxyecdysone, a molting hormone in invertebrates, induces the high mortality rate in test animals at higher concentrations but neither reduced the reproduction rate nor increased the development into males. These results indicate that the development of D. magna into males is not caused by the chemical stress but by the endocrine disruption. Finally, the offspring sex ratio in D. magna can be a useful endpoint to detect the endocrine disrupting effect by juvenile hormones analogs.
Key words: fenoxycarb, sex determination, IGR, juvenile hormone