Sex Chromosomes of Rana rugosa with Special Reference to Local Differences in Sex-determining Mechanism

Nishioka Midori

Miura Ikuo

Saitoh Kazuo

Scientific report of the Laboratory for Amphibian Biology

The karyotypes of the two populations, Kumano and Hirosaki, of Rana rugosa were compared with each other by the methods of conventional Giemsa staining, C-banding and LR (late replication)-banding. It was found that in the Kumano population, the 13 pairs of chromosomes are completely homozygous and there are no chromosome pairs which have any sexual differences, while chromosome pair No.7 of the females in the Hirosaki population are heteromorphic and constructed of a subtelocentric Z and a metacentric W chromosome. The W chromosome also distinctly differs from the Z chromosome in both C-band and LR-band patterns. It is probable that the W chromosome was induced from the Z chromosome by two inversions on the basis of the LR-band pattern. In the Kumano population, nearly all of the females are changed into males by injection of testosterone propionate at the tadpole stage. The offspring of the sex-reversed genetic females mated with normal females are almost females. This seems to show that the Kumano population of Rana rugosa is of the XX-XY type. In the Hirosaki population, it has been confirmed by the methods of conventional Giemsa staining, C-banding and LR-banding that this is of the ZW-ZZ type and there are no frogs whose sex is reversed by injection of testosterone propionate. Sex ratios were examined in the offspring of reciprocal crosses between the Kumano and Hirosaki populations. It was found that the offspring (XZ) between the females (XX) of the Kumano population and the males (ZZ) of the Hirosaki population are almost all males, while the offspring (WX, WY, ZX, ZY) between the females (ZW) of the Hirosaki population and the males (XY) of the Kumano population include nearly the same number of females and males. It was quite evident that almost all the frogs having the W chromosomes were females, while all the frogs having the Z chromosomes were males, regardless of the existence of the X or Y chromosome.

Zoology [ 480 ]

eng

Institute for Amphibian Biology, Hiroshima University

[ISSN] 0386-3166

[NCID] AA00837669