title: Production of male neonates in four cladoceran species exposed to a juvenile hormone analog, fenoxycarb.
abstract: Previous studies have found that exposure of a cyclic parthenogen, the water flea Daphnia magna (Cladocera, Crustacea), to juvenile hormones and their analogs results in the production of neonates of male sex at concentration-dependent rates. We conducted reproduction experiments in four different species (Moina macrocopa, M. micrura, Ceriodaphnia dubia and C. reticulata) of cladoceran to test for the first time whether the occurrence of this phenomenon after exposure of the parent to such hormones is a generalized phenomenon. In the presence of a juvenile hormone analog, fenoxycarb, all four species produced male neonates and showed reduced rates of reproduction. The estimated median effective concentration (EC50) for the production of male neonates varied with species, ranging from 0.60 x 10(3) to 9.3 x 10(3) ng/l. Although there was a wide range of sensitivity to fenoxycarb, the production of male neonates in all four species demonstrates that this phenomenon is a common response to juvenile hormone analogs and further suggests that these hormones are capable of initiating sexual reproduction in cladocerans, most of which exhibit cyclic parthenogenesis.
authors.affiliation: Endocrine Disrupters and Dioxin Research Project, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 304-8406, Japan. oda.shigeto@nies.go.jp
authors.forename: Shigeto
authors.initials: S
authors.lastname: Oda
authors.forename: Norihisa
authors.initials: N
authors.lastname: Tatarazako
authors.forename: Hajime
authors.initials: H
authors.lastname: Watanabe
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Morita
authors.forename: Taisen
authors.initials: T
authors.lastname: Iguchi
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D033361:Cladocera / Q000502:physiology*; D005260:Female; D007306:Insecticides / Q000633:toxicity*; D007605:Juvenile Hormones / Q000633:toxicity*; D008297:Male; D048448:Phenylcarbamates / Q000633:toxicity*; D012098:Reproduction / Q000187:drug effects*; D012744:Sex Ratio
chemical_list: D007306:Insecticides; D007605:Juvenile Hormones; D048448:Phenylcarbamates; C052034:fenoxycarb