2016 Volume 63 Issue 2 Pages 45-54
Acute and chronic effects of colchicine on the freshwater cladoceran Daphnia magna were examined, based on a 48-h acute immobilization test and a 21-day reproduction test with female neonates, respectively. The 48-h EC50 value of colchicine to neonates was 24 mg L-1. In the reproduction tests, NOEC was 0.2 mg L-1 and more than 0.5 mg L-1 of colchicine showed a significant effect on embryogenesis and stopped embryo development. In the following embryo developmental inhibition test, embryos burst within 48–72 hours after oviposition in the brood chamber, when embryos within 5 hours after oviposition were exposed to colchicine at 1 mg L-1. Colchicine inhibited the early embryogenesis, but did not affect the gastrulation or organogenesis. As a result of nuclear staining test, the embryos exposed to colchicine at 1 mg L-1 continuously in the ovary showed normal cleavage until at least 4 hours after oviposition, but the specific fluorescence intensities of nuclei had almost disappeared at 24 hours after oviposition. These results indicate that 1) oogenesis in ovaries of D. magna is not inhibited by colchicine, 2) 1 mg L-1 of colchicine inhibits the cell division of embryos at 24 hours after oviposition although its inhibition effect is delayed, 3) more than 0.5 mg L-1 of colchicine inhibits early embryogenesis, and 4) 0.5–1 mg L-1 of colchicine causes bursting of embryos. The latter two results are remarkable, but its mechanism remains unresolved in the present study.
