DIFFERENCES IN GENETIC BACKGROUNDS AFFECTING GONADAL DIFFERENTIATION BETWEEN 2 LOCAL-POPULATIONS OF THE JAPANESE WRINKLED FROG (RANA-RUGOSA)

Gonadal differentiation in two local populations - Hamakita and Hirosh ima - of the Japanese wrinkled frog (Rana rugosa) was examined from ha tching to the end of metamorphosis. The Hamakita male has X and Y chro mosomes distinguishable morphologically from each other, while X and Y chromosomes in the Hiroshima male cannot be distinguished morphologic ally. In the two populations, primordial gonads differentiated into te stes or ovaries by stage I of Taylor and Kollros, and larvae at stage XXV - the end of metamorphosis - possessed definitive testes or ovarie s. However, immature testes at stages II-III in the Hiroshima populati on showed a higher incidence of testes with ovarian characteristics - meiotic figures and gonadal cavities - than those in the Hamakita popu lation. In addition, proliferative activities in the testicular cells of the immature testes in the Hiroshima population were very low. On t he other hand, there were no remarkable differences in the histologica l processes of ovary development between the two populations. Intraspe cific hybridization between females of the Hamakita population and mal es of the Hiroshima population retarded testis differentiation after s tage XV, while the reciprocal hybridization showed normal gonadal sex differentiation and development. These observations suggest that R. ru gosa, possessing heteromorphic sex chromosomes in the male, establishe s firm gonochorism, where the feminization involves the suppression of testis differentiation, and that masculinization is performed by resi stance to this suppression as well as active proliferation of testicul ar cells.