PARENT SESSION
PT2 - Endocrine Disruption
Tuesday, 19 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P570) Insecticides for juvenile hormone agonists exert the influence on the occurrence of the male daphnid.
Tatarazako, Norihisa*,1,3, Koshio, Masaaki1, Kawabe, Kiyoshi1, Morita, Masatoshi1, Watanabe, Hajime2,3, Iguchi, Taisen2,3, 1 National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan3 CREST, JST (Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation), Shibuya, Tokyo, Japan2 Center for Integrative Biology, Okazaki National Research Institutes, Okazaki, Aichi, Japan
ABSTRACT- The water fleas, Daphnia magna, reproduce by cyclic parthenogenesis as a predominant strategy. Environmental stimuli, which indicate a change to adverse conditions, signal the organisms to switch from parthenogenesis to gamogenetic reproduction. During gamogenetic period they produce male daphnia and dormant resting eggs, which can survive prolonged periods of environmental adversity. But little is known about the switching mechanism from parthenogenesis to gamogenetic reproduction. In this study, we found that pyriproxyfen and fenoxycarb, which are known as juvenile hormone agonist, reduced the production of offspring and that they produce male daphnia. Exposure of either one of the chemicals at 330ng/L concentration caused adult female to produce all male neonates. When exposure of pyriproxyfen or fenoxycarb was stopped at 21st day and continued to rear the culture in clean water, male neonates were not born after seven days later. This result indicates that the effect of priproxyfen or fenoxycarb is reversible but not persistent effect and that this changing of the male production system takes about one week. When adult daphnid producing only female was treated with 1000ng/ L of fenoxycarb or pyriproxyfen for 1week, all neonates produced one week later after chemical treatment were male. These results suggest that one week is necessary to change the reproduction system. On the other hand, methoprene, another insecticide as juvenile hormone agonist that have no phenoxyphenoxy group had no ability to produce male daphnid. Our finding suggests that the phenoxyphenoxy containing insecticides affect the biomolecule responsible for the reproduction switching.
Key words: daphnid, pyriproxyfen, fenoxycarb, male production