1995 Volume 20 Issue 2 Pages 95-108
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.