Sexual maturity, ovulation mode, litter size, gestation period and longevity of captive Anderson's red-backed voles Eothenomys andersoni from the Kii Peninsula were investigated on 22 voles (9 males and 13 females) captured from December 1988 to March 1990, and 84 offspring of the 2nd and 3rd generations bred from the above wild-caught voles. As the result, the presence of spermatozoa in males began to be recognized on day 60, and all females had perforated vaginas by day 90, when they attained sexual maturity. The ovarian ova were found to be in prophase of the meiosis I in estrus but unmated females, and entered into metaphase of the meiosis I 5 hr after coitus. Ten hr after coitus, the ova advanced to metaphase of the meiosis II just before ovulation. Fifteen hr after coitus, the fertilized ova reached either pronucleus formation or metaphase of the 1st cleavage, and 20 hr after coitus the ova were at the two-celled stage. Accordingly, it was revealed that the time required for reflex ovulation after coitus was between 10 and 15 hr. The gestation period was 20 days, and the litter size of the wild-caught generation was 3.88 (n=25), which was considered incongruently small, given the presence of eight mammae. The maximum life-span recorded was 1,243 days for females and 1,098 days for males, and the physiological longevity was considered to be nearly 3 years.
Both Watase's Crocidura watasei and musk Suncus murinus shrews possess cardiac myocytes in the tunica media of the intrapulmonary venous walls. Cardiac musculature was found even in the small intrapulmonary veins. Immunohistochemical studies demonstrated the presence of atrial natriuretic polypeptide (ANP) in the musculature. ANP-immunoreactivity was observed in the cardiac myocytes of intrapulmonary veins of more than 200 μm in diameter. It is suggested that pulmonary venous cardiac musculature evolved as an endocrine apparatus in insectivores such as Crocidura and Suncus.
The reproductive activity of captive Apodemus argenteus was observed in detail from 1986 to 1989, and 149 births were recorded. Parturition occurred throughout the year, but peaked from March to July. Reproductive activity of the live-trapped generation did not differ from that of the second, third or fourth generations. Litter size was 4.21 on average, and the earliest age at first parturition was three months. The time interval between successive births was 33.6 days on average, the shortest being 20 days. Sexual behavior was also observed, and a necessity for experience was indicated.
The karyotypes of the Japanese northern red-backed vole Clethrionomys rutilus mikado and the Japanese gray red-backed vole C. rufocanus bedfordiae were reexamined using chromosome banding techniques. Both mikado and bedfordiae were confirmed to have 2n=56 and FNa =56, and no chromosomal variation could be detected between them so far as the conventionally stained material was concerned. Detailed G-banding analysis, however, revealed distinct interspecific variations in two pairs of acrocentrics (Nos. 1 and 9). These chromosomal variations could be explained by a reciprocal translocation, t(1; 9)(q21; q16), which was regarded to be the same as the 1-9 translocation described from C. glareolus by Gamperl (1982a). Both of the chromosomes concerned (I and 9) were homomorphic in all of the 44 specimens collected from five different localities in Hokkaido, Japan, as revealed by either G-or Q-banding pattern. Therefore, C. rutilus mikado is considered to have been genetically fixed as stable homozygotes throughout their whole population. Furthermore, the G-banded karyotype of C. rutilus mikado was found to be identical with that of the Alaskan northern red-backed vole C. rutilus. It is concluded, therefore, that northern red-backed voles, irrespective of their locality or subspecies, carry the 1-9 translocation as a specific karyotypic character.
Microhabitat selection in two closely related sympatric species of Clethrionomys, C. rex and C. rufocanus bedfordiae, was examined in a forest in northern Hokkaido, Japan. Multivariate analysis revealed that discrimination in the use of microhabitats was dominated by vegetational and topographic variables (correlation ratio=0.681). C. rex was commoner than C. rufocanus in valley bottoms and on rather moderate slopes, with mixed undergrowth of Sasa bamboos and herbage. In spite of differential use of microhabitats by males and females, individual voles were segregated interspecifically rather than intraspecifically.