The copulatory behavior pattern of house musk shrews paired for 24 h starting at either 09:00 (light) or 20:00 (dark) was investigated. Ejaculatory behaviors were observed in both light and dark periods, when mating was started at 09:00. However, the males ejaculated only in the dark period when they were paired at 20:00

Hashimoto, Haruo

Saito, Toru R

English

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IntroductionHouse musk shrews (Suncus murinus) are known tohave an alimentary canal more structurally similarto that of human beings than rats or mice(Kurohmaru, 1985), to be sensitive to motion sick-ness (Kaji et al. 1990), and to be more resistant toX- rays than C3Hf/He mice (Tsubouchi et al.,1984). They have been widely used in studies ondisease models for motion sickness, gastric cancer,and hematopoietic disorders. They are also expect-ed to be models for hormone-dependent tumorsbecause of their spontaneous, androgen-dependentpilosebaceous tumor (Itami & Takayasu 1983,1984). Knowledge of their reproductive efficiencyis needed for such research. It is considered thatmatured female house musk shrews with reflexovulators are ready to mate with males at any time.Recently Hashimoto et al. (2004) investigatedwhether a male house musk shrew could impreg-nate more than one female within 24 h. In the present study, we focused our attention onthe appearance of ejaculation during 24 h in malehouse musk shrews when first paired in the light ordark.Materials and MethodsAnimalsTen sexually experienced male and female 1-year-old house musk shrews of the Jic: SUN strain weresupplied from the Central Institute forExperimental Animals (Kawasaki, Japan). The ani-mals were housed in polycarbonate cages (220 deepx 380 wide x 200 high mm) with wood shavings asbedding in an animal room kept at 24± 2˚ C and55± 10% humidity with a 12:12h light:dark cyclewith lighting on at 07:00. They were given CLEA-305 diet (CLEA Japan, Inc., Tokyo, Japan) and tapwater ad libitum. All experiments were performedunder the Guidelines for Animal Experimentationof the Japanese Association for Laboratory AnimalScience.Mating systemsEach male was paired with a single female for 24 h.The male was introduced in a cage first and was fol-lowed 5 min later by a female at either 09:00 (lightgroup) or 20:00 (dark group). Behavior was record-ed with a video camera. A 6W red light bulb illumi-nated the cage during the dark period. The followingindices of copulation were measured according tothe method reported by Saito et al. (1997).1) Mounting frequency (MF): Number of mount-ings without intromission during 24 h.2) Intromission frequency (IF): Number of mount-ings with intromission during 24 h.Scand.  J. Lab. Anim. Sci.  No. 1.  2005. Vol.  3241House Musk Shrews (Suncus murinus) Do Not Copulate in theLight Period when First Paired in the Dark by Haruo Hashimoto and Toru R. Saito*Behavioral Neuroscience Laboratory, Department of Biomedical Science, Nippon Veterinary and Animal Science University, Musashino, Tokyo, Japan.SummaryThe copulatory behavior pattern of house musk shrews paired for 24 h starting at either 09:00 (light) or20:00 (dark) was investigated. Ejaculatory behaviors were observed in both light and dark periods, whenmating was started at 09:00. However, the males ejaculated only in the dark period when they were pairedat 20:00.*Correspondence: Toru R. Saito, DVM, MSc, PhD,DJCLAM, Department of Biomedical Science, NipponVeterinary and Animal Science University, 1-7-1 Kyonan-cho, Musashino-shi, Tokyo 180-8602, Japan. Tel & Fax: +81-422-31-4571. E-mail: trsaito@nvau.ac.jpScand.  J. Lab. Anim. Sci.  No. 1.  2005. Vol.  32423) Ejaculation frequency (EF): Number of ejacula-tions during 24 h.4) Mounting latency (ML): Time elapsed betweenintroduction of the female and the first displayof mounting.5) Intromission latency (IL): Time elapsed betweenintroduction of the female and the first displayof intromission.6) Ejaculation latency (EL): Time elapsed from thefirst intromission to ejaculation.After observations of copulatory behavior, matedfemales were checked for delivery rate and littersize. Litter size was defined as the number of pupsat 0 day after birth.Statistical analysisDifferences in copulatory behavior between the twomating groups were compared with the Mann-Whitney U test, and differences in rates of deliverywere analyzed with the Fisher’s exact probabilitytest. In all tests the two groups were compared at asignificance level of 0.05.Results and DiscussionAs shown in Figs. 1 and 2, when mating was start-ed at 09:00 (light period) ejaculations wereobserved in both light and dark periods (defined as“light period patterns” in Fig. 1), while they wereobserved only in dark period (defined as “darkperiod patterns” in Fig. 2) when mating was startedat 20:00 (dark period). A copulation sequence inhouse musk shrews consisted of ejaculation after some mounts and intromissions. In addition,all males ejaculated in all sequences observed inthis study (Figs. 1 and 2). This is similar to mice,rat, Syrian hamsters, and a former study on housemusk shrews (Hashimoto et al. 2004, Hokao et al.1993). As shown in Table 1, the frequencies and latenciesof copulation were not different between the lightand dark groups. The delivery rate and litter sizewere not significantly different between the twogroups (Table 2).Saito et al. (1997) reported that the numbers andlatencies of mounts, intromissions, and ejaculationswere not significantly different when 2-h matingwas started either at 09:00 (light period) or 20:00(dark period). The copulatory behaviors wereobserved for 24 h in both light and dark periods,and the males ejaculated only in the dark periodwhen they were paired at 20:00.Such a phenomenon has never been reported inother species of animals. It is interesting to consid-er the cause of no ejaculations occurring in the lightperiod when first paired in the dark. Unfortunately,the authors currently can offer no suggestions.Further studies are necessary to clarify this point.Figure 1 Figure 2Scand.  J. Lab. Anim. Sci.  No. 1.  2005. Vol.  32AcknowledgementsThe authors thank Dr. T. Yamaguchi, Brain Scienceand Life Technology Research Foundation,Itabashi, Tokyo, Japan, for his helpful advice. ReferencesHashimoto H, N Moritani & T R Saito: Copulatorybehavior and fertility of male house muskshrews (Suncus murinus) paired with one, twoand four females each. Exp Anim, 2004, 53, 53-56.Hokao R, T R Saito & K W Takahashi: Comparisonof sexual behavior patterns in small laboratoryanimals. Exp Anim, 1993, 42, 451-455.Itami S & S Takayasu: An androgen-dependentpilosebaceous tumor spontaneously developedin the Japanese house musk shrew Suncusmurius. J Steroid Biochem, 1983, 19, 1141-1146.Itami S & S Takayasu: Serial transplantation to nudemice of an androgen-dependent pilosebaceoustumor developed in Suncus murinus. CancerRes, 1984, 4, 5666-5669.Kaji T, H Saito, S Ueno & N Matsuki: Comparisonof various motion stimuli on motion sicknessand acquisition of adaptation in Suncus muri-nus. Exp Anim, 1990, 39, 75-79.Kurohmaru M: Characteristics of the gastrointesti-nal tract of the house musk shrew. In: Suncus(K.Kondo, ed.) Japan Scientific Societies Press,Tokyo, 1985, p.p. 389-396.Saito T R, H Hashimoto, N Moritani, K Taniguchi &KW Takahashi: Copulatory behavior of malehouse musk shrew (Suncus murinus). Scand JLab Anim Sci, 1997, 24, 143-146.Tsubouchi S, E Kano & S Oda: Dose-survival timeresponse of Suncus murinus from whole-bodyirradiation. J Radiation Res, 1984, 25, 234-245.43

House Musk Shrews (Suncus murinus) Do Not Copulate in the Light Period when First Paired in the Dark

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House Musk Shrews (Suncus murinus) Do Not Copulate in the Light Period when First Paired in the Dark

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