Variations of the Number of Embryos in Microtus montebelli (Milne-Edwards)-香川大学学術情報リポジトリ

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VariationsoftheNumberofEmbryosinMicrotusmontebelli

(MILNE−EDWARDS)*

YukibumiKANEKO BioIogicalLaboratory,FacultyofEducation,KagawaUniversity,

Takamatsu,Japan

ABSTRACT.−Thedistributionofembryosinuterin¢horns,SeaSOnalchangesofbody Weightinpregnaptfbmales,andrelationbetweenthenumberofembryos,bodysize and age of pregnant fbmales,micro−habitat and season were describedin肋rotus

monlebelli.Number of specimens,Which were co11ected on ricefield,ricefieldin fallowandyoungplantation,WaS84.Therewasnostatisticallysignificantdeviation fromarandom distributjonofembryoswithintheuterus.Theaveragebodyweight

Ofpregnantfbmalessubtractingtheweightofembryoswasnotsignificantlydi鮎rent

duringayear.Theaveragenumberofembryosincreasedfromclass6to8andde− CreaSed fi.orn class9tollinage−grOupOfpregnantfヒmales.Therewasatendency

that theaverage bodyweight ofpregnantftmalesincreasedwiththeincreaseofthe

numberofembryosatthesameclassin age−grOup.Thenumberofembryosinthe SameWeightofpregnantftmalesonleveeswaslargerinSeptemberthaninMay.A

COmParison between two neighboring Octoberpopulations showed that the number

Ofembryosinthesamらbodyweightwaslargeronricefieldinfallowthaninyoung

plantation.Itissuggestedinthisvolethatthedifferences offoodqualitybrought aboutthevariationofthenumberofembryosofthesameageandbodysizeofpreg− nant fbmalesindi庁brentmicro−habitatsinthesameseasonand/orindi飴rentseasons in thesamemicro_habitat. Introduction

Ithasbeenwe11knownthatthenumberofembryosorlittersizevaries和ithseason,

year,body size,POPulation density,▲habitat,altitude andlatitude.Severalpapers

havebeenpublishedinMicrotusn−Omwi1dpopulationsinEuropeandNorthAmerica

onth占variationofthenumber極relationtoage,SeaSOn,year,habitat,bodysizeand

latitude(JAMESON,1947;BEE正et∼al.,1957;BEER&MACLEOD,1961;KoTT&

RoBINSON,1963;NEGt)$&PINTER,1965;TAST,1966;EvANS,1973).IntheJapanese

丘eld vole,Microtus montebelli,however,ftw works have been carried out on the

Variationofthenumberofembryos,eXCePtthefbllowlngPaPerS:thenumberchanged

WithseasonduringayearinalocalityinJapan(MIYAOetdl.,1966;SHIRAISHI,1967;

ABE,1974;KANE竺0,1976)andwithhabitatsinneighboringOctoberpopulationsin

ayear(KANEKb,1978b).

ThepresentpurposeofthispaperistOdescribethedistributionofembryosin

uterinehorns,SeaSOnalchangesofbodyweightinpregnantftmales,andtherelations

betweenthenumberofembryos,bodysize−andageofpregnantfbmales,micro−habitat

andseasonintheJapanesefieldvoie,Microtusmontebelli(MILNE−EDWARDS).

*ContributionNo.40fromtheBiologlCalLaboratory,FacultyofEducation,KagawaUniversity.

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哺乳動物学雑誌 Vol.7,No.3

122

Materials and Metbods

Inthisstudy84specimens oftheJapanesefield volewere taken on rice丘eld,

ricefieldin fallow and young plantationin the fbllowlngfivelocalitiesinJapan:

Morioka,Iwate Pref.;Ry6zu,Niigata Pref.;Iwakura,Kyoto Pref.;Jinsekiand

Kurome,HiroshimaPref.;and Fukuoka,FukuokaPref.The specimens caught at

Iwakura,JinsekiandKuromewerethesameaspreviouslydescribedinKANEKO(1976,

1978a&b).Thespecimenswerecapturedbysnap−traPSWithpumpkinseedsasbait.

Al1fbmaleswereweightedandtheirbodysizesweremeasured.Thenumberofvisible

embryosinbothhornsoftheuteruswascountedwiththenakedeye,andthetotal

weightofembryoswasmeasuredincludingthefbetalmembranesanduterus.Body

weightsubtractingtheweightofembryoswas■uSedasthatofeachpregnantfbmale.

Theclassinage−grOuP Ofpregnantftmaleswasdeterminedbythemorphology

ofoccipitalprocessandridges,Whichwasdescribedinthepreviouspaper(KANEKO,

1978a).

Sincetherewasagoodcorrelationbetweenbodyweightandthelengthofhead

andbody(KANEKO,1978a),bodyweightofpregnantftmaleswasusedasbodysize.

R(さSⅥ1ts and】Discussion

l)Distributionofembryosinuterinehorns

Thenumberofvisibleembryosin40volesrangedn・OmtWOtOnineinthe1971−

72collectionsofIwakura,Kyoto.Theincidenceofunilateralpregnancywas7.5%

(3/40)and two specimens wereleft side pregnancies and one was right side.The

PrOPOrtionofbilateralpregnancieswithequalnumbersofembryosinbothhornswas

15.0%(6/40).Therewasnosignificantdeviationn・Omarandomdistribution(Poisson

distribution)ofembryoswithintheuterus,aCCOrdingtoax2testasshowninTablel

Tablel.Thedistribution ofembryosbetweenleft(Lt)andright(Rt)uterinehornsof 助川助∫椚♂〝Jg∂d〃atIwakum,Kyoto,197ト72. Difrbrenceinnos. No.ofvoles

ofembryosbetween Distribution betweenhorns Observed

(total) Expected no.(∽) borns Lt>Rt Rt>Lt (6) ′LU 5 1 7 0 1 1 1 2 0 つJ 4 2 0ノ 00 3 0 5 2 0 1 1 0.590 0.308 0.379 0.474 2.200 0.011 ズ2=3.962 O l つー3 4 5 00 5 4 0 1 7 ‘U つJ O O x,=difftrencebetweentheobservedandexpectednumberofanimals.Variance(sり=0.653・

(0.25<p<0.5).ThesamefindingwasobtainedinM.montebelliinFukuokaPre仁

bySHIRAISHI(1967)andinM.penn叩IvanicusandM.ochrogasterbyCoRTHUM(1967).

D Seasonalchangesofbodyweightinpregnantftmales

Inthe40specimensofIwakura,Kyoto,1971−72,thesma11estweightofpregnant

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atIwakura,Kyoto,1971−72.

Month N Range(g) Meanj=SE(g)

May Sept. Nov. Jan. Mar. 32.5−38.9 29.9−41.5 27.7−38.5 22.6−29.2 26,0−37.1 7 4 7 3 ¢U l 3(5.13土.98 35.93土.83 32.26土1.50 25.27士2.00 33.04±1.25

ftmaleswas22.6ginJanuary,andthelargestwas4l.5ginSeptember(Table2).The

averagemonthlyweightoftheftmalesvariedftom25gto36g.Theaverageweight

WaS nearly equalthrough ayear exceptJanuary,When

Althoughtheaveragenumberofembryosdi鮎redstatisticallyamongmonthsexcept

between March and May(KANEKO,1976),the averageweightwas not significantly

di飴rent among six months.The mean bodylength ofpregnant fbmales did not

Change seasona11ythroughthebreedingseasonin ClethrionomysandbrsoniandApo−

ゐ∽〟∫α曙e〃fe〃∫(MIYAO,1969).

3)Thenumberofembryosagainstclassesinageqgroupofpregnantfemales

Thevisibleembryosappearedatclass6inage−grOuPintheIwakurapopulation,

Kyoto,1971−72.The average number ofembryosincreased ftom class6to8and

decreasedftomclass9tollduringayear(Table3),thoughthedifftrencebetween

Table3.Thenumber ofembryos under various classesin age−grOupin Microtus montebelliatIwakura,Kyoto,1971−72.The statisticaldifference between Class8andclass6was O.2<p<0.3and the difftrence between other classes exceptclassllwasp>0.6. No.indi鮎rentnumberclassesofembryos n p .1 u eS rO SS瑠 a e l Cag No.ofembryos (Mean±SE) 2 3 4 5 6 1 1 2 7 1 1 4 8 9 Total 12 4.6土.4 2 9 5.6士.8 1 4 5.8士1.2 6 5.2±.5 1 4 ‘U 7 00 q/ O 1 1 1 2 1 2 つん 2 2 1

Classesexceptclassllwasstatisticallyinsignificant・NEGUS&PINTER(1965)demon−

StratedinM・mOntanuSthatthelittersizeincreasedgraduallythroughthefifthcon−

SeCutivelitteranddecreasedthefbllowlnglitter.

Acomparisonofthenumberofembryos‘atthesameclassinage−grOuPShowed

that thelarge number occurredin September;While the smallone was fbundin

January(Fig・1)・Therefbre,thenumberofembryosatthesameclassinage−grOuP

Ofpregnantftmaleschangedwithseasons.

4)Relationshipbetweenthenumberofembryosandweightofpregnantftmales

InFig・2thenumberofembryosisplottedagalnSttheincreaseofbodyweight

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哺乳動物学雑誌 Vol.7,No.3 124 。T 困刷冊SE脚 nU・ム 臼 ● ○

9 8 7 る 5 4 3 2 1

SOと芯≦山]○。OZ b ● ● 吐 血 血 nU O ・△ 0

3 4 5 る 7 8 9101112

ÅGE−GROUP

Fig.1.Scatter diagram of the relationship between classin age−grOup and the numberofembryosinMicrotusmontebelliatIwakura,Kyoto,197ト72. 0 9 8 7 d 5.4 3 2 1 SO≧垂烹〓〇.〇Z 0」AN,tr=−0.占d4) ム仙AR.=「=†0.る65】 ロ八AY け=†0.140) ●SEPT.け=†0.d35) O NOV.け=二0.089j ● ロ ●●臼 ●● 鎗 附● ●ム血● 00 ()A o dコ 0 ム 8 8 0 30 BODY WEJGHT(g) 40 Fig.2.Scatterdiagramoftherelationshipbetweenthenumberofembryosandbody WeightofpregnantfemalesinMicrotusmontebelliatIwakura,Kyoto,1971−72.

Bodyweight subtractingtheweight ofembryoswasusedasthat ofpregnant

females.The coe伍cient ofcorrelation(r)in each month was shownin this 負gure.

goodrelationbetweentheweightofmothersandthenumberofembryosina11the

SamPles during ayear(r=0.647).There was not so apparent correlation between the twoin each month(Fig.2),eXCePtin September(0.01<p<0.02).Heavier

ftmaleswithlargenumberofembryoswereobservedinSeptember,Whilelighterftmale

WithsmallnumberofembryosoccurredinJanuary.

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bryos under various classesin age−grOupin MicrotLES montebelliatIwakura, Kyoto,1971−72. Mean*bodyweight(g)indifferentnumber Classesofembryos

Classes

111 age−grOuP Mean士SE 8 9 2 3 4 5 6 7 26.0 29.1 32.00土.97 40.3 35.01土1.85 39.1 34.98土2.23 35.72±.68 38.5 33.7 34.6 34.7 35.6 2夕.2 ′b 7 8 0ノ O 1 1 1 33.0 22.6 31.3 37.4 36.3 33.9 35.4 38.2 38.5 *NumberofspecimenswasgiveninTable3.

thesame classin age−grOuP(Table4).Therewas atendencythatthe averageinq

creasedwiththeincrease ofthenumber ofembryos atthe sameclassinage−grOuP・

AccordingtoBEERetal.(1957),therewasasteadyincreaseinnumberofcorporawith

increaseillbodylenBth.Furthermore,they showed thatthe totalintrauterineloss

variedinverselywiththesizeofftmalesinM.pennsylvanicusandC.gqpperi.There−

fbre,the number ofembryos atthe same classin agergroupincreasedwith thein−

CreaSeOfbodysize.

5)Thenumberofembryosindi鮎rentmicro−habitats

The number ofembryos changed seasonallyinfourdifrerentmicro−habitats on

cultivatedland atIwakura,Kyoto,197ト72(Table5).The di飴rence of average

number ofembryos between di鮎rent micro−habitats was thelargestin September

amongfivemonths,thoughthedi鮎rencewasstatisticallyinsignificantin September

(0.1<p<0.2).In Septemberthe vegetation ofleveesinfallowlandswascomposed

mainly ofPob)gOnum thunbergii,Commelina communis and Cherus microiria,and

Gb)Cinemaxwasplanted on severallevees.Threepregnantftmalesweretakenon

fallowlandinJanuary(Table5),When fallowland was densely overgrown with

Withering Solidqgo altissimain abotlt2m height,and young Soli‘わgo altissima

Table5.Thenumber ofembryosin variousmicro−habitatsin difrbfent mOnthsin MicrotusmontebelliatIwakura,Kyoto,1971−72.Each尽gurerepresentsnumber Ofembryosofeachpregnantfemale≡collectedineachmicro−habitat.:Number inparenthesesshowstheaveragenumberofembryos.

Agricultul−al road‥‥D Fallowlandsdensely Grass−grOWnlevee Levee

inね1lowユand ユnrlCe ‥.B 丘eld….C 0VergrOWllWjth ふ痛血酢=油盆山那 ‥‥A 5,6(5.5) 4,5(4.5) 5 6,7,9,9(7.8) 5,5,5,5,5, 7 5,6,9,9(6,0) 4,4(4.0) 4,4,4(4.0) May 4,5,7(5.3) Sept. Nov. 2,4(3.0) Jan. 2,2,3(2.3) March 5 3,4,4,5,5, 5 5(4.3)

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Vol.7,No.3 哺乳一動物学雑誌

126

sproutedatthebaseofthewitheredroots・

FromTable6,itislikelythattheaveragenumberofembryosindi能rentmicro−

habitats on ricefieldinfallowdidnot so greatlyvaryin May,June,August and

Octoberinsevera1localitiesinJapan.

A8C l ● l O ム

︵ソ 8 7.〇 5.4 3

S2∝山王山L〇.〇Z

A ∞ム Ol ム○● ムム息ム血 1

30

40

BODY WE)GHT(g)

20

50

Fig.3・Scatterdiagramoftherelationshipbetweenthenumberofembryosar)dbody

weightofpregnantfemalesinMicrotusmontebelliindifferentmicro−habitatsat

Iwakura,Kyoto,1971−72.A;fallowiand densely overgrownwith Sb肋如 altissima,B:Grass−grOWnleveeinfallowland,C:Leveeinricefield・Open

symboIsrepresentspecimensinSeptember,andsolidonesshowspecimensin

May. 7 ′0 5 .4 3 つ‘ SO>出血王山 ﹄〇.〇Z 00 0 000 ■l 00● ○ ● ●● ● ● ● ● ●

20 30 40 50

BODY WEtGHT(g) Fig.4.Scatterdiagramoftherelationshipbetweenthenumberofembryosandbody weightofpregnantfemalesin凡打crotusmontebelHinneighboringOctoberpopu− 1ations,HiroshimaPref.,1972.Opencirclesrepresentfemalesonricefieldin

fallowandsolidonesshowfbmalesinyoungplantations.

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コ ト.刊?寸 仇 M.刊﹁寸 p−ひ唱 Z 国S¶ロ召∑ 0−qd−亀ぎ JO∽払p佃銘 打︶ コ ︵∞.巴∽ゼゼ 寸.刊∽.れ ゼゼゼべれM m.刊○這 ぷp

Sき○竜∽OS月︶岩岳d点J月日nZ pdOh ︻空n︸ち0叫払く ︵巴 ︵?寸︶れhM や ︵﹁己れれれ れ音へ寸れMれM ︵?示︶ り.れれ寸 心小人ひJ rq︶ .sOh−q己ごOJOq己2=払巴璧ゐ﹄華 .︸眉q遥占JO叫∈竜dOひ︸8−ちじ書宍喜騙苫垂論ビd ざ.豊 トゼれれ ︵∞.寸︶ れーれ.れへれれれ寸 ︵竺寸︶り㌦.れれ寸寸 ︵∞.巴 トドぜ.れれ叫れれ p日月き0コd u叫0りAひ﹂ ︵U︶ く芭00琶 pロdlき○∃虎 口き○誌・S∽已0 ︵巴 ∽りS∽d︼叫 L≡き星g払 ﹂J診○とOS宕p p白虎lき○コd﹄ ︹く︶ やU−qd↑ M卜巴 さ羞=d琶nづ広 Nト仇︷ −月○︸00 3ひ∽月ヽ ︻トのー ︺sコ地コV コZ叉亘 Mトヘ︻ へ告nトムd∑ ぷ○叫旨∑ 重石○苫 き叫1日OJ

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哺乳動物学雑誌 Vol.7,No.3

128

Sincethenumberofembryosatthesameclassinage−grOuPlnCreaSedwiththe

increase ofbodyweight(Table4),COmParisons ofthe numberin the same weight

Weremadeamongdifftrentmicro−habitats(Fig.3).Thenumberinthesameweight

OnleveewaslargerinSeptemberthaninMay(B&CinFig.3).Itfb1lowsthatthe

number ofembryosin the same weight ofpregnant ftmales collectedin the same

micro−habitatchangedwithseasons.

Inthepreviouspaper(KANEKO,1978b),habitatdi飴rencesbetweenneighboring

Octoberpopulationsbroughtaboutthevariationoftheaveragenumberofembryos,

throughbothpopulationswereconsideredtobethesameinagecomposition・Figure

4showsthatthenumberofembryosinthesamebodyweightislargeronricefieldin

fallowthaninyoungplantation.

Summaringthesefindingsabovementioned,COmParisons ofthe same size and

age showedin Microtus montebellithat the number ofembryos changed primarily

Withthedi飴renttypesofmicro−habitatinthesamecollectingperiodandwithseasons

inthesamemicro−habitat.AlthoughEvANS(1973)showedinM.agrestisthatthere

WerenOSignificantdifrbrencesinpotentiallittersizesbetweenyoungplantationand

limestone grassland,NEGUS&PINTER(1966)revealedin M.montanus that small

dietary supplements ofeither sprouted wheat or acetone−ether extracts ofsprouted

Wheatelicitedimprovedreproductiveperfbrmance・Furthermor?,theydemonstrated

thattheimprovementresultedprimarilyinmorefiequentpostpartummaitings and

lower rates oflitterloss.Therefbre,itis suggested that the di鮎rences of food

qualitybroughtaboutthevariationofthenumberofembryosinthesameageand

Size ofpregnant ftmalesin diffbrent micro−habitatsin the same season and/orin

di飴rent seasonsin the samemicro−habitat.

Acknowledgement

IwishtothanktoDr.Y.FuJIMAKIforreadingandcriticizlngthemanuscript・

摘 要 金子之史:ハタネズミにおける胎児数の変化 水田,水田休耕地および君命造林地で採集した84個体のハタネズミ妊娠雌について,胎児の左右 子宮内での分布,妊娠雌の体重の季節的変化,および胎児数と妊娠雌の体重・年令,捕獲された微小 棲息場所,捕獲時期との関係を調査した。 1.子宮内の胎児の分布のし方ほ,ポアソソ分布から統計的に有意な差を示さなかった。 2.胎児体重を差し引いた妊娠雌の体重は,1年間で有意な差は示さなかった。 3.平均胎児数は妊娠雌のage−grOup6から8にかけて増大し,9から10にかけて減少したが,統 計的に有意のある差ではなかった。 4.同一クラスのage一許Oupの妊娠雌で比較すると,胎児数の増加は妊娠雌の平均体重の増加に伴 なっていた。 5.畦で捕獲された同一体重の妊娠雌における胎児数は,5月よりも9月の方が大きかった。 6.同時期に採集した近接した2個体群内の同一体重の妊娠雌の胎児数ほ,水田休耕地の方が若令 造林地よりも大きかった。

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棲息場所の異なった採集時期,および同一時期に採集した異なった微小接点場所,によってもたらさ れる食物の質のちがいによって変化することが示唆された。

Refbremces

ABE,T.1974.An analysis ofage structure and reproductive activity of MicrotLLSmOntebel[lpo− pulation based on yearly trapping data.Jap.J.appl.Ent.Zool.18:21H27.

BEER,].R.&MACLEOD,C.F.1961.Seasonalreproductioninthemeadowvole.J.Mamm.,42: 483−−489. + &Franzel,L.D.1957.Prenatalsurvivalandlossinsomecricetidrodents.].Mamm., 38:392」102. CoRTHUM,K.WM.,Jr.1967.Reproductionanddurationofplacentalscarsintheprairievoleand theeastemvole.J.Mamm.,48:287−292. EvANS,D.M.1973.SeasonalvariationsinthebodycompositionandnutritionofthevoleMicrot〟S L7greStis.,.Anim.Ecol.,42:1−8. HoFFMANN,R.S.1958.Theroleofreproductionandmortalityinpopulationfluctuationsofvoles (ル打cro拍∫).Ecol.Monograph,28:79−109. JAMESON,E.W.,Jr.1947.Naturalhistoryoftheprairievole(MammaliangenusMicrotus).Univ. Kans.Publ.Mus.Nat.Histリ1:125−151. KANEKO,Y.1976.ReproductionofJapanesefieldvoles,Microtusmontebelli(MILNE−EDWARDS),at Iwakura,Kyoto,Japan.Jap.].Ecol.,26:107−114. 1977a・SeasonalandsexualdifrerencesinabsoluteandrelativegrowthinMicrotusmontebelli・ Actatheriol.,23:75−98. 1977b.Acomparison ofnumberofembryosandmeasurements6fMicrotusmontebelliin twotypeSOfhabitats.Actatheri01.,23:140−143. KoTT,E.&RoBINSON,W.L.1963.Seasonalvariationinlittersizeofthemeadowvoleinsouthern Ontario.J.Mamm.,44:467−171. MIYAO,T.1969.Thesma11mammalsonMt.YatsugatakeinHonshu.IX.Thenumberofembryosin Ch?thrionomys andkrsoniand Apodemus aYgenleusin the subalpine forest zone on Mt.

Yatsugatake.ShinshQ−Honyurui−KenkyukairKaih6,(6):1T5.(InJapanese).

,MoROZUMI,M.&MoROZUMI,T.1966.Smal1mammals ofMt.Yatsugatakein Honshu VI.Seasonalvariationin sex ratio,body weight andreproductioninthevole,〟7crotus

JJ旧JJJビ占tイ/J. NBGUS,N.C.&PINTER,A.,.1965.LittersizesofMicrotusmontanusinthelaboratory.J.Mamm., 46:4封ト437. 、 &+ 1966.Reproductiveqespo払cesofMicrotusmontan〟StOPlantsandplantextractsin thediet・J・Mamtnリ47:596−601・ SHIRAISHI,S・1967・Some River−bed,KurumeCity・J・MamplぎSoc・Japan,3:57−63・ TAST,).1966.Therootvole,Microtusoec♭nomus伊ALLAS),aSaninhabitan!ofseasonally800ded land.Ann.Zool.Fennici,3:127−17l.

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