In only a few vespertilionine bats, it has been experimentally proved that spermatozoa retain the fertilizing ability over a period of 6 months in the female reproductive tract. However, there have been few studies focussed on implications of such prolonged sperm storage from the viewpoint of capacitation. In the Japanese house bat, reliable evidence for delayed capacitation was provided by experiments which were designed to vary the duration of sperm storage in the female genital tract. As the duration was lengthened from 4-5 to 150-166 days, each ratio of egg activation and normal development increased from 0% to 100%, suggesting that delayed capacitation evolved with prolonged sperm storage in the heterothermic bat. Thus, both sperm storage and heterothermy seem to be closely associated with the delayed capacitation which is regarded as an adaptive character of spermatozoa in bats.

View full 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.

View full abstract

Chromosomes of Sorex caecutiens shinto, S. c. saevus, S. unguiculatus and S. gracillimus were compared in detail based on the G and C-banding patterns, paying attention to the structural variations of their No. 5 chromosomes. The first three had the diploid number of 42, and carried prominent satellites on the short arms of the pairs Nos. 19 and 20, but the last one (2n=36) only on the short arms of No.17. These satellites seemed to function as active NORs, being differentially stained by the one-step silver-staining method which was applied only to S.c. shinto in the present study. The caecutiens complex and S. unguiculatus were almost identical in their G-banding pattern as well as in their chromosome constitution, except for the No.5 chromosomes slightly differing from one another in the arm ratio and/or G-banding pattern. These chromosomal variations could be explained by two kinds of pericentric inversion rearrangements. S. gracillimus was highly homologous in the G-banding pattern with the caecutiens complex and S. unguiculatus in spite of a marked differentiation in the karyotype, sharing the identical pattern of G-bands with S. unguiculatus in almost 92% of its total chromosome length. The pair No. 5 of S. gracillimus was identical in the G-banding pattern with that of S. unguiculatus. The phylogenetic relationships of these four species and subspecies of Sorex were briefly discussed from a karyosystematic viewpoint.

View full abstract

Karyotypes and Gimsa-banding patterns of Clethrionomys montanus and C. rufocanus bedfordiae are examined. The two have the same diploid number (56) and FN (58), and similar G-bands. The autosomes consist of 26 pairs of acrocentrics decreasing gradually in size and 1 pair of the smallest metacentrics. The X chromo-somes are the 4th acrocentrics, and the Ys the smallest acrocentrics. Chromosome variations explained by pericentric inversion are found on the pairs of No. 18 chromosome of C. montanus and No. 5 chromosome of C. r. bedfordiae. A close relation between the two species is suggested on the basis of the chromosomal survey and the intraspecific variation of the enamel patterns of molars found in some Clethrionomys species.

View full abstract

Age and sexual variations of eight cranial dimensions in the least horseshoe bat, Rhinolophus coynutus, were examined by classifying 225 males and 219 females from four populations into seven age groups. There were two groups of dimensions which had different tendencies in growth. In females the mastoid width ceased growth at an early stage of age and the other dimensions increased until age group III. In males, the mastoid width and the height of brain-case stopped growth at an early stage of age and the other characters increased until age group II. No clear sexual dimorphism was found in any dimension until two months of age, but appeared thereafter in most of the dimensions, i, e., those of males increased more rapidly than did those of females. However, the dimorphism disappeared again at age group III. The width across upper molars grew faster in females than in males ; the zygomatic width did not show sexual dimorphism after age group I. In the analyses of samples pooled of all age groups, most of the male characters had a tendency to be larger than those of female, excepting the width across upper molars, which was significantly greater in females than in males and the zygomatic width, which did not differ between sexes. Accordingly, it was pointed out that attention for these variations should be paid to compare cranial dimensions in the studies of classification and geographic variation of this species.

View full abstract

In field studies of the Japanese serow Capricornis crispus, age and sex determination is very difficult because of its small horns and little sexual dimorphism. Methods of age and sex determination are considered in the field study which was conducted in Tsutomuzawa National Forest, Akita Prefecture, Japan during 1979-1985. Age-classes were basically divided into four by horn shapes ; kids (less than 1 year old), yearlings, subadults (2 years old), and adults (3 years old or more) . Kids were easily distinguished by their no or small horns. Yearlings and subadults had one to several thicker rings of horns than older serows, although distinction between 2 and 3 years of age became difficult usually in and after autumn. Absolute clues for the sex determination were obtained from observations of the external genitalia, the teat, suckling behavior, and the spot of excreting urine. A series of male sexual behavior and accompanying of kids were applied as secondary clues, when these types of behavior were repeatedly observed. In 91% of 159 identified serows (1 year old or more) and 47% of 119 kids, the sex was determined by those criteria.

View full abstract

The parturition of Lepus brachyurus brachyurus in captivity took place in a shallow den (-5 cm in depth and - 20 cm in diameter) dug by the mother, and its duration was very short (-2 min) . Newborn young quickly acquired locomotive ability and could run about ca. 1 hr after delivery. They began to feed on some plants at day 8, but were nursed until 1 month after birth. They usually suckled at midnight only once a day for ca. 2 min, and the mother and her infant (s) separated except at the nursing time. The parturition and nursing behaviours in this hare showed a similarity to those of rabbit-type species. However, a distinct difference between Lepus and rabbit-type species is that Lepus is reproductively independent of the burrow (nest) by virtue of its ability to bear precocious young. This uniqueness seems to give Lepus advantages over rabbit-type species, by minimizing the energy investment of the mother for parturition and nursing, reducing the risk from predators, and increasing the infant's locomotive ability.

View full abstract

Eighty-four specimens (34 females and 50 males) of the feral mink (Mustela vison) were collected in Hokkaido. It was at first confirmed that the annual layer in a canine was formed from autumn to winter in Hokkaido, and then the age of specimen (n=76) was determined by the annual layer. The proportion of 0⁺ year animals was 63.2% of the total samples ; the oldest age was 5⁺ years in male, and 6⁺ years in female. Juveniles grew as large as adults (over one year old) by November (approximately six months old) . The sexual difference in size of adults (male/female) was 1.56 in body weight and 1.13 in head and body length. The sex of an adult could be determined by the length of mandible in most cases.

View full abstract