本州八ヶ岳のネズミおよび食虫類-2- Small Mammals on Mt. Yatsugatake in Honshu. : II. Seasonal Differences of sex Ratio, Body Weight and Reproduction on Apodemus argenteus and Clethrionomys andersoni in the Subalpine Forest Zone on Mt. Yatsugatake.
The authors investigated the seasonal differences of sex ratio, body weight, percentage of pregnant female and testicle size in two species of the field mice, Apodemus argenteus and Clethrionomys andersoni, collected from April, 1962 to March, 1963, in the subalpine forestzone (Tsuga diversifolia-Abies Mariesii forest zone, alt. 1,800-2,400m) on Mt. Yatsugatake in Honshu. Toral number of collected specimens was 308 Apodemus ar genteus and 616 Clethrionomys andersoni. 1) The number of males was larger than that of females in all months except August in Clethrionomys andersoni (♀ 56.7%), and July in Apodemus argenteus (♀ 54.6%), during the height of the breeding season (Fig. 1). 2) From the histograms of the body weight, the following tendencies were noted. Young mice appeared from July to October in Clethrionomys andersoni, and from June to September in Apodemus argenteus. Old adults disappeared from November to March in Clethrionomys andersoni, and from August in Apodemus argenteus. In both species, the developmental period of body weight generally coincided with the spring breeding season (Fig. 2 and Fig. 3). The life span of these species was supposed at about 1 year. 3) The maximum monthly pregnancy rate was attained in June in both species (Fig. 4). The yearly average embryo size was 3.3 in Clethrionomys andersoni and 3.9 in Apodemys argenteus. 4) The monthly average testicle sizes were about 10 mm. from April to July in both species. But they were about 4 mm. from October to March (Fig. 5).
動物学雑誌 72(7), 187-193, 1963-07