Abstract
Reproduction in the Smith's red-backed vole, Eothenomys smithii, was investigated under laboratory conditions. A total of 188 litters produced by 39 females from three generations were used in this study. Litter size was 4.45 (a range of 1-9) en bloc, showing no significant difference between these generations. The sex ratio of 540 young in 124 litters was 1 male : 0.97 female (274 : 266) . The shortest and most frequent litter intervals were day 19 and day 22, respectively. Post-partum mating was common. The maximum number of litters per a female was 19. The oldest female at parturition was 980 days old ; the oldest male sired a litter at 1, 180 days of age. The maximum longevity was 1, 280 days. Compared with other well-studied microtine species in the reproductive parameters, E. smithii possesses a relatively great reproductive capacity. As to litter size of this species, mean litter size in a laboratory colony exceeded mean embryo counts (4.1 in Kyushu and -2.5 in Honshu and Shikoku) in wild populations. On the basis of this fact, it is concluded that reproduction ofE. smithii is apt to be influenced by its life environment and field conditions seem to suppress its reproduction.
