Global decline of population size and species in amphibians during the last few decades has been discussed among environmentalists and biologists for possible causes [lJ. Although various factors such as chemical or physical agents affecting environmental integrity have been considered as possible casuses for the decline, no decisive evidence has ever appeared [2J. Adult anuran amphibians usually do not drink water orally, but intake it mainly through a part of their ventral skin. We have previously shown that Japanese tree-frogs show sexual dimorphism in water absorption in the ventral skin. We examined the influence of an insecticide, methoxychlor, which has been known as an endodrine disruptor in modifying sexual integrity of animals, on the cutaneous water absorption of Japanese tree-frogs. After being kept for one month in water containing methoxychlor, male tree-frogs showed apparent depression of the cutaneous water absorption rate at concentration of 10-6 M or higher, but the agent had no effects on the females up to 10-5 M. When frogs were brought into a dehydrated environment after being kept in water containing methoxychlor for one month, all animals, males and females, showed a marked depression of the water absorption rate even at a low concentration of 10-9 M. These results suggest one possible reason for the severe decline in the amphibian population during 1960s when the agent had been widely used [3J, may be due to disability of the water absorption caused by the endocrine disruptors
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