The EcologicalSocietyEcological Society of Japan Ntil2kftst (Jap, J. Ecol.), 31: 247-256, 1981 REPRODUcrIVE IN CLETHRIOIVOMYS RUFOCAIVUS BEDFORDIAEACTrvITY4. NUMBER OF EMBRYOS AND PRENATAL MORTAI,rltYi) Yluzo FUJIMAKI,Laboratery of PVildtijli Resource Eceiqgy,, Obthiro U}tiversityofAgriculture arid P;eterinary Medicine, Obihiro 080 = V'Vf*-' .: Oecvatsnt4 . ta va tu t di fii ntu fi t ' rstaIEv(#"thitthlo`elfeemza$ wt g ws di Synopsis FunMAKi, Yuzo (Lab. Wildl. Resou. Ecol., Obihiro Univ. Agric. Vet. Med., Obihiro). 1981. Repro- ductive activity in CZethrionomys rnjbcanus becefordiae 4. Number of embryos and prenatal mortality. Jap.J.Eco1.31:ZtP7-256. Variatjons in the number of embryos of Clethrionomys rtofbcanus beeUbrdlae were cxamined using 747 pregriant fernales obtained from various areas of Hokkaido in 1967-1974. The numberofem- bryos per pregriant female ranged from l to 10 and averaged 5.3. The mean was srnaller than that in high latitudes of th6 Eurasian Continent: However, regional variation was not recognized within Hok- and 5.2inOctober. The number of kaido. Tbe mean pumber of ¢ mbryos was 5.9 in June, 4.8 in August embryos tended to increase with advanoed age and increased body weight of females, but it decreased in females of 12 months old. Thus the declinein the number ofembryos in August and October was at- tributed to advanced ago in overwintered females and recmitnrent of young fernales to the population, There was no difference in the number ofembryos between primiparous females and multiparous ones, Tbe number of corpora lutea per pregnant female ranged from 2 to 14 and averaged 6.1. Prenatal loss ef embryos was found in 36.0% of the 439 pregnant females examined. The prenatal mortality was 9.0% for overwintered females and 16.5% for females of the year, and it increased with the increas- ing number of corpora lutea. major roles in determining the pattern of popula- Introductien tion fluctuation. FuJiMAKi (1972, 1973, 1975) lhe red-backed vole, CVlethrionomys reijbcanus investigated regional variations in the reproduc- betUZ}rdiae, is disuibuted in Hokkaido, Japan, as a tive activity of the species throughout Hokkaido common inhabitant of forests, brushy areas, and in relation to the population trend, and found oocasionally grassy areas. Many papers have been that in the southern part, the enset of breeding - published on its ecological distribution, reproduc- was earlier in spring and the termination was later tion, food habits and flycLuation (see in autumn than in the northern and eastern parts. population 'aspects UEDA et al., 1966). Since these papers were based T he present study aims to show several on data obtained from only one or a few locali- of variations in the pumber of embryos and the ties, they do not present a wide perspective on the prenatal mortality in the red-backed vole based on species' breeding biology throughout Hokkaido. the data obtained from various areas ofHokkaido. It is well known that the'vole shows a high am- Materials and Methods plitude of population fluctuations in northern and eastern et al., 1966; FuJiMAKi, trapping was carried out at sites in Hokkaido (UEDA, The 40 1971). However, the mechanism of these fluctua- Hokkaido during the months of June, August tions has not been clarified because of insuMcient arid October in evefy year from 1967 to 1974 (Fig. knowledge about birth and death playing the 1). Each site censisted of young Larix ioj)tolqpis or Abies sachalinensis plantation (O.5 ha) and its Aooepted Dec. 17, 1980 neighboring area (O.5 ha). The trapping methods 1) Contribution from the LaboratQry of Wildlife Re- used were described elsewhere 1972)- source Ecology, Obihiro University of Aghculture and (FuJiMAKi, trapped were weighed and pre- Veterinary Medicine, No. 33 AII of the females 247 NII-Electronic LibraryMbraryService Service The EcologicalSocietyEcological Society of Japan Vel. 31. No, 3 H* th me #k ss Sep., 1981 .LiY'tt 31 4S..lo-3rD -T9tll- ss -ZB-34- TII V { tl [V VI .?1-"' 44o Fig. 2. Age classes based on the groove closing and Lir)..x:iilc!",,'25' root forrmation in the upper socond molar. 13. ;V!1,. .14Xl.t2t{3fiE:S19' -11t12 dla"-4--.-5rN6 were foTmed, but they were less than 1!3 of the Bs.7t IT -io-gN-?ox whole length of M2 ; V: the roots were 113 to 1/2 of the ]ength ofM2; VI: the roots wcre more than ta-1N A3 1/2 of the length of M2. The females of the year 41. -!1 belonged to age classes I and II in June, I to III in August, and I to V in October, Overwintered females were in age class IV to VI in June, V and Fig. 1. Locations of sampling sites and five areas in VI in August, and VI in October (ABE, 1976). Hokkaido. 1; Esashi, 2: Hakodate, 3: Meri, 4: Hekkaido was dividedinto 5 areas, A, B, C, D, rrnagene. 5: Toyoura, 6: Soubetsu, 7: Urakawa, and E 1) according to the pattern of popula- 8: Mitsuishi, 9: Biratori, 1O: Hayakita, 11 : Yoichi, (Fig. tion fluctuations and the reproductive activities of 12: Sapporo, 13: Toubetsu, 14: lwarnizawa, 15: Bibai, 16: Fukagawa, 17: Rumoi, 18:Touma, 19: the species. As has been reported, in D and E the Biei, 20: Taiki,21: Toyokoro, 22: Ashoro, 23: voles increase abruptly in number from spring to Oketo, 24: Rubeshibe, 25: Kitami, 26: Abashiri, autumn, exhibiting a high amplitude of popula- 27: Obira, 28: Haboro, 29: Shozanbetsu, 30: Te- tion fluctuations, whiie in A and B, they inerease shio, 31: Hamatonbetsu, 32: Nakatonbetsu, 33: slightly from spring to autumn. [[he population BifUka, 34:Nayoro, 35: Okeppe, 36: Akan, 37: trend in C is intermediate between thes¢ two pat- Akkeshi, 38: Shibecha, 39: Bekkai, 40: Nakashi- terns 1971). In A the breeding season betsu. (FuJIMAKi, extends from mid-March to late October, an in D and E from mid-April to mid-October. The re- served in IO% formalin so]ution to examine the productive activity in summer is more intense in D uterus, ovarjes and upper second molar. Of a total and E than in A. The onset and termination of the visible seasons, and the of reproductive of 3415 femalescaptured, 747 (21.9%) had breeding degree embryos in their uterus. [(lhe numbers of preg- actjvity in B and C are intermediate between nant femares captured were yariable from year to these ofA and E (FuJiMAKi, 1972, 1973, l975). year: 44, 50, 128, 94, 154, 71, 111 and 95, respec- Results and Discussion tively during the 8 year examination period. The number of visible embryos in the uterus was count- Regiona} yariation in the number of embryos ed with the naked eye, but that of the plaoental The rnean numbers of embryos in the 5 areas sears was not consideTed. Ihe number of embryos are given in Table 1 . The mean ranged from 3.7 to in one litter did not include the resorbing ones. 5.2 in June, 4.1 to 5.0 in August, and 5.0 to S.5 in The number of corpora lutea in the ovaries was October for the females of the year. The corre- counted with the naked eye in 439 ofthe 747 preg- sponding valiles fbr overwintered females were nant femaies,Tliebody weight of the pregnant 5.6to 6.2,4.1 to 5.0,and 4.7 to 6.0 , respect:vely females was determined by subtracting the weight (Table 1). No significant differences were found ef the embryos. among the 5 areas in the respective months in the The ages of the pregnant females were deter- overwintered females as well as in the females of mined aecording to the groeve closing and root the year (Student t-test, P>O.1). The combined formation in the upper second rnolar (M2) as il!u- data ofthe three months in one area did not reveal strated in Fig. 2. As shown, I: the grooves did not any significant difTbrences in the mean among the close at the basal tip of M2; II: the grooves were 5 areas in either of the age groups (P>O.1). In closed at the basar tip; III: after closing of the PreviOus papers (FuJIMAKI, 1972, 1973. 1975), of grooyes, the neck grew; IV: two separate roots there were some indicationsthatthe number 24g NII-Electronic Library Service The EcologicalSocietyEcological Society of Japan VoL 31, No. 3 JAPANESE JOURNAL OF ECOLOGY Sep,, 1981 Table 1. The number of embryos (rnean [l SE) in females of the year (above) and in overwintered females (belew) obtained from fivc areas of Hokkaido in 1967-1974 (see Fig. 1), Aiea .Whole Overallfemales A B C D Ezz area Number of females 111 113 97 184 242 747 examined June 5.2±O.46.04.8± O.46.15.0± O.65.63.7± O.96.24,2± O.56,OtO.2S.O4.8± 026.1 5.9± O,1 ±O.24,1 ± 024.2 ± O.34.9 ± O,24.S ± O.14,8 August ±O.34.1 ± O.24.8 ± O,35.0 ± O.25.0 ± O.1 ± O,14.84,8± O.1 ±O.45.4 ± O.352 ± O.35.5 ± O.25.04.6± O.35,1 ± O.152 October ± O.25.4 ± O.34.9 ± O.36.e ± O,26,O ± O.44,7 ± O.15.35.2± O.] ± O.25.2 ± O,44,8 ± o.s5.1 ± O.64.6 ± O.5S.O ± e,24.9 June to October ± O.25.6 ± O.25.8 ± O.25.5 ± O,15.7 ± O.1S.5 ± O.15.6S.3± O.1 ± 02 ± O.2 ± O.2 ± O.1 ± O.2 ± O.1 embryos for the overwintered females was larger Table 2.