variation

9. Geographical Variation of Some Characters in Wild Populations

By N. Egami

Various characters of the medaka, such as several meristic characters, proportion of a part of the body, body size, development of the secondary sexual characters etc. were compared among natural wild populations with many specimens collected at different localities.

Among these characters, significant difference in mean number of the anal fin rays was clearly demonststrated among specimens collected in different areas (Egami, 1953; Fukui and Ogawa, 1957; Egami and Yoshino, 1958). In total 5982 specimens collected at 125 localities were examined and the results given diagrammatically in Figure 9-1 were obtained. Some crossing experiments between fish obtained at different localities were carried out, and it was conluded that the character is controled by actions of polygenic genes (Egami, 1954). From these, it is clear that there are many isolated wild populations in this fish in nature.

Various mutants of body color and other characters were found from the fish collected at different localities (see chapter 20), and it is suggested that gene frequency is different among fish populations in different areas.

Recently it was demonstrated that the reactions of fish gonads to photoperiod were different among fish populations caught in Hokkaido, Niigata, Tokyo and Okinawa (Sahara and Egami, unpublished data). From this fact it is likely that differentiation in physiological characters is proceeding among isolated populations in Oryzias latipes.

References Egami, N., 1951 Genetic veriation in the fin ray number of Oryzias latipes. (Abstract, in Japanese.) Japan. J. Genetics 26: 242.

Egami, N., 1953a Geographical variation in the number of the anal fin rays and of the vertebrae in Oryzias latipes. (Abstact, in Japanese.) Japan. J. Genetics 28: 164.

Egami, N., 1953b Studies on the variation of the anal fin rays in Oryzias latipes.ЕЯ. Geographical variation in wild populations. (In Japanese.) Japan. J. Ichthyol. 3: 33-35, 87-89.

Egami, N. and M. Yoshino, 1958 Studies on the variation of the number of the anal fin-rays in Oryzias latipes. Еб. Supplementary note on the geographical variation in the wild populations. (In Japanese). Japan. J. Ichthyol. 7: 83-88.

Fukui, T. and Y. Ogawa, 1957 Variation in numbers of anal fin rays in Oryzias latipes collected in Ishikawa Prefecture. (Abstract, in Japanese.) Zool. Mag. 66: 151.

Ogawa, Y., 1955 Notes on the ecological variation of the number of fin rays of wild Oryzias latipes collected from Noto-district, Ishikawa. (In Japanese.) Collecting and Breeding 17: 274-277.

Ogawa, Y., 1958 On the local variation in the number of anal fin-rays of Japanese killifish, Oryzias latipes in Tajima district, Hyogo Prefecture. (In Japanese.) Collecting and Breeding 20: 48-51.

Fig. 9-1. Map showing the localities. Circle shows diagrammatically the mean number of the anal fin-rays in the fish population collected at each locality. Egami, 1953b.