Gonadal differentiation in frogs, Rana japonica and R. brevipoda, raised from UV irradiated eggs.

Abstract

The gonadal differentiation of anurans, Rana japonica and R. brevipoda, was examined in animals raised from eggs which had been irradiated at the vegetal hemisphere with UV (9300 erg/mm2) at the 2-cell stage. In R. japonica about 70% of the larvae at stage I from the pressed and UV-irradiated eggs were germ cell free, but at a stage immediately after metamorphosis all animals had at least some germ cells, although their gonads often were extremely small and poorly differentiated. When male animals matured sexually, many of them had abnormal gonads. However, all of them were shown by artificial means to be capable of fertilization. In the nonpressed and irradiated group, no larvae were germ cell free and the animals immediately after metamorphosis showed nearly normal gonadal differentiation except for the presence of a few degenerate oocytes in the ovaries. The results in R. brevipoda were basically similar to those in R. japonica. In both species, sex ratios were determined at two stages, the first immediately after metamorphosis and the other when the animals matured, as based on gonad morphology and histology and on external sexually dimorphic characters as well. Sex ratios at these two stages in frogs from the pressed and irradiated eggs differed markedly in R. brevipoda. The ratio was normal at metamorphosis but high M/F ratios occurred when animals became mature. That sex reversal took place in this species as well as in R. japonica (in which sex-ratio deviation was not statistically significant) was supported by the sex ratios of the progenies of these supernumerary males.