MARDI Res. Bul l . (1986) l4(3), (189-201)

SOME OBSERVATIONS ON THE REPRODUCTION, GROWTH ANDDEVELOPMENT OF MAS CAROLI IN CAPTIVITY

Y.M. LAM*

Keywords: Mus caroli, Post-natal growth and development, Litter size, Sex ratio.

RINGKASAN

Kaj ian pembesaran dan perkcmbangan anak t ikus (Mus carol i \ selepas lahir te lah di ja lankan di

dalam makmal. Si fat-s i fat pcmbcsaran dan perkembangan te lah dikaj i dengan te l i t i dan di terangkan.

Bi langan anak purata pada masa lahir ia lah 4.3+0.4. Berat badan purata bagi jantan dan bet ina pada

masa lahir masing-masing ia lah 1.02+0.02 g dan 0.96+0.02 gram. Bcrat anak t ikus pada masa lahir

ber jumfah antara 14.5%, hingga 46.14/ t , berat badan t ikus bet ina ( ibu), dengan purata 30.0+2.6 peratus.

Bi langan anak t ikus jantan didapat i melebih i b i langan bet ina dengan nisbah jant ina 2.2: L Perkembangan

anak t ikus selcpas lahir boleh dibahagikan kepada empat fasa: neonatal ( l -8 har i ) , keadaan peral ihan

(9-15 har i ) , berkemasyarakatan (16-21 har i ) dan remaja (22 har i h ingga kematangan jant ina).

INTRODUCTION

The rice field mouse. Mus caroliBonhote. was first recorded in SouthKedah, Peninsular Malayaia in 1976(LnNcHnrvr and LAM, 1977). I t was found inthe rice fields and was occupying burrowsdug into the bunds separat ing the r ice p lots .Mus caroli is widely distributed in SoutheastAsia and it has been recorded in the RyukuIs lands, Taiwan, Hainan, Yunan, Vietnam,Thai land, Sumatra, Java, Madura andFlores (Er-lenunN and MoRRISoN-Scorr,1951). I t is a pest of r ice f ie lds and poul t ryfarms in Thailand (MnnsHnt , 1977). Litt leis known about its reproduction, growth anddevelopment. This paper presentsobservations made on the reproduction,growth and development of M. caroli incaptivity.

MATERIALS AND METHODS

The laboratory colony of mice wasobtained from the rice fields at Titi Batu.Kampung Perigi and Teroi Tua in southKedah. The mice were kept in an animalhouse measur ing 5.1 m x 10.2 m, undernormal l ighting and environmentalconditions. The mice (9 pairs) werepermanently paired in cages of strong wire(mesh 3 .5 mm x 3 .5 mm) , measu r i ng 31 x 31x 21 centimetres. These cages were placed

on trays with paddy husks (about 2.5 cmdepth) as absorbent l i tter. These husks werechanged at least once a week.

A commercia l laboratory mouse pel le t(Gold Coin Sdn. Bhd.) supplemented wi thunhusked rice grains were provided adlibitum. The specifications of the mousepcl le t were g iven by Lnv (1983).

The female mice were checked dailyand when they were v is ib ly pregnant ,nesting materials such as dry grass or ricestraws were provided for nest building.When the young were born, they were sexedby using the ano-genital distance (Dnvrs,1964), measured, weighed and examined.The weight of the dam was also recorded.The day of birth was designated as day one.The litter size, birth weight and head andbody length were recorded. Birth weightswere recorded to the nearest 0.05 gramme.Post-natal developmental characteristics ofthe young were studied. Dailymeasurements and observations were madeup to 2l days and thereafter, measurementswere made at weekly intervals. The youngwere weaned at 21 days and groupedaccording to sex for observation andmeasurement .

When removing the young forobservation and measurement. care was

*Ricc Research Div is ion, MARDI, Bumbong Lima. Kepala Batas, Penang. Malaysra.

189

Table 1. Physical measurements of Mus caroli atbirth

Measurements (Mean +S.E. )Bir thweight

(e) Head & bodylength (mm)

Tail length(mm)

Hind foot Ano-genital

length (mm) distance (mm)

Male(n:34)

Female(n : I 7 )

1.02+0.02

0.96+0.02

28.32+0.23

2 8 . 3 5 + 0 . 1 7

1 0 . 9 1 + 0 . l 3

1 0 . 7 1 + 0 . 1 9

4.97 +0.03

4.94+0.06

1.40+0.03

0.67+0.01

n = number of mice

taken to minimize disturbance of the nest.The parents were first removed from thecage. After examination and measurement,the young were replaced into the nest andthe parents returned to the cage. As theyoung grew older and became very active,they were anaesthesized with diethylether tofacil i tate measurement. All the standardphysical measurements and weight of theyoung were recorded in mill imetres andgrammes respectively.

RESULTS

Litter Size and Sex Ratio

The mean litter size of 14 l itters bornin the laboratory was 4.3+0.4 and the l ittersizes ranged from two to seven. There wasno significant correlation between the weightof the dam and litter size (F-ratio; l inearregression : 1.39; quadratic regression :

0.21; I d . f . ; P>0.05) . In the 14 l i t tersobserved, mean weight of the dams was14.6+0.3 g, with a range in weights of 12.6-16.4 grammes.

The sex ratio of the young born wasmarkedly in favour of males; 41 malesversus 19 females, a ratio of 2.2:1, whichdeparted significantly from the expectedra t i o o f 1 :1 (X2 : - 4 .03* ; 1 d . f . ; P<0 .05 ) .

Size at Birth

The weight of the individual male pupsat b i r th var ied between 0.75 g and 1.25 gand that of the females 0.80 g and 1.1,5grammes. The head and body length (HBL)of male pups at birth varied between 25

mm and 30 mm and that of the females 27mm and 30 millimetres. The various physicalmeasurements of M. csroli at birth are givenin Table 1. The mean weight of the maleswas 1.02+0.02 g and that of the females was0.96+0.02 grammes. There was no signifi-cant difference in the mean birth weightsbetween males and females (F : 3.97; Id . f . ; P>0.05) . The mean HBL of males was28.32+0.23 mm and that of females was28.35+0.17 mm (Table 1) . There was nosignificant difference in the mean birth HBLbetween males and females (F : 0.01; 1d . f . ; P > 0 . 0 5 ) .

Gross weights of the l itters rangedfrom 2.I g for a l itter of two to 6.8 g for alitter of six. The mean total birth weight ofthe l itters was 4.4+0.4 grammes. When thebirth weights of the l itters were expressed asa percentage of the weight of the dam, themean was 30.0+2.6Vo, with a range of14.57o-46.4 per cent. However, there wasno significant correlation between the weightof the dam and total weight of l i tter (F-ratio,l inear regression 1.55, quadraticreg ress ion : 0 .27 ;1 d . f . ; P>0 .05 ) .

The mean weights of individuals fromlitters of various l itter sizes are given inTable 2. There was no significant differencebetween the means of the various groups(F:2.38; 5 d. f . ; P>0.05) . The re lat ionshipof l i tter size. individual and total birthweights showed significant l inear correlation(Figure 1). The birth weight of the young

was negatively correlated with l itter size (r: - 0 .3 * ; 1 d . f . ; P<0 .05 ) wh i l e t he t o ta lbirth weight was positively correlated tol i t t e r s i ze ( r : 0 .96* * ; 1 d . f . ; P<0 .01 ) .

190

Table 2. Number of young per litter and mean weight of young at birth for Mus caroli

No. in l i t ters

Sample size

Mean wt.+s.8. (c)

I

1 . 05+0 .05 1.03+0.03

I

I . 09+0 .04 0.99+0.02 1.02+0.03 0 .91+0.03

7 .0

6.0

5 .0

4 .0

3.0

2 .0

)= 0.3t3+0.92rr=0.96* "P<0.01

Table 3. Birth sequences and intervals of afemale Mus caroli

114F

33

36

27

1.0-s

0.95

0.8,s

-

!

=

Birthsequence

Birthinterval(days)

Littersize

Wt. ofdam (g)

14 .45

t 4 . l 0

1 4 . 1 5

t4 .80

14.00

1 5 . 6 5

1 4 . 5 0

_r ' :1 .11-0 .02- tr : -0 .30-P<0.05

2 3 . 1 5 6 7Litter size

Figure 1. The relationship of litter size,individual birth weight and total birth weight

in Mus caroli.

Birth Sequences and Intervals

One female was very prolif ic and hadnine l itters in one year (Table 3). Theshortest birth interval recorded for thisfemale was 23 days and the longest 114 dayswith a mean of 42.4+10.4 days. There wasno significant relationship between thepreceeding l itter size and birth intervals (r :0 .25 ; I d . f . ; P>0 .05 ) .

Growth, Morphological and BehaviouralDevelopment from first to 98th day afterBirth

Day 1 The young were pink and(<12 hours) hairless except for the

presence of short unpig-mented mystacial, super-cil iary, submental, genal andinteramal vibrissae. Thelongest mystacial vibrissawas about 1.5 mm long. Thesupercil iary vibrissae com-prised one long and one shortvibrissa. Submental vibrissaewere present as two shortunpigmented bristles. Theupper and lower genalvibrissae were present as twoshort unpigmented bristles.The upper and lower genalvibrissae had one and twobristles respectively. Milkcould be seen in the stomachof young. Umbilical scar was

5 14 .50

6 14.65

191

Day 2

vis ib le. Nai ls were ev identon the toes and the d ig i tswere fused. The skull l ineformation was visiblethrough the sk in. Mammaein the females were notapparent. No sign of pig-mentation was found in thefuture scrotal region of themales. Eye p igments wereapparent through the closedlids. Eye slits appeared asgrooves on both eyes. Theear pinnae were folded withve ry s l i gh t p i gmen ta t i on a tthe edges. The males couldbe separated from thefemales by the greater ano-genital distance in the males(mean : 1.40 + 0.03 mm formales and 0.6 '7 + 0.01 mmfor females) and also thelarger s ize of the penis inmales compared with thecl i tor is in females. Theaverage weights of the malesand females were 1.02 g and0.96 g, with the correspond-ing HBL of 28.32 mm and28.35 mm respectively(Table I \ .

The skin colour of the youngwas sti l l pink but slightlydarker . Pigmentat ion on thedorsum at the shoulders wasevident . No hai r was con-spicuous either on the dorsalor ventral part of the body.More unpigmented hair hadsprouted at the submentalregion. The muzzle regionwas more prominent . g iv ingthe young a snout appear-ance. The hair papil lae ofthe supercil iary and genalvibrissae were more con-spicuous. Female mammaewere sti l l not apparent. Footpads were slightly pigmented.Umbilical scar was sti l l

present . The skul l l ine for-mat ion was st i l l v is ib lethrough the sk in.

Day 3 Pigmentat ion began to takeform on the head anddorsum but hair had noterupted from body. No pig-menI was conspicuous on thefront and h ind legs. The ta i land legs were st i l l p ink.More pronounced swel l ingin the muzzel region gave theyoung a snout appearance.The skin was more wrinkledand hai r papi l lae on the bodywere more distinct. Thelongest mystacial vibrissawas 2.6 mm. the longersuperc i l iary v ibr issa was 1.4mm and the shorter one was0.7 mm; and the genalv ibr issae were 0.9 mi l l i -metre. However. hai r werest i l l unpigmented. Theabdominal mammae infemales could be distin-guished. The Y-shaped skul ll ine on top of the head wasbarely v is ib le as the sk inbecame more opaque. Theear pinnae were sti l l fused tothe head. Young were st i l lunable to crawl except forsome c i rcu lar movement.The umbilical scar and milkin the stomach were sti l l 'v i s i b l e .

Day 4 The young were darker on

the dorsal parts and had

acquired very short, sparse,

unpigmented hai r on the

dorsal part of the head and

body. No hair had sprouted

in the venter of the young.

Pigmentation had extended

from the nose to the dorsal

par t of the ta i l . No p igment

had formed on both front

t92

and hind feet but there waspigmentation on the footpads. Pigmentation was moreprominent on the tuberclesand the digital toes of thehind feet. The supercil iaryvibrissae were pigmented atthe basal hal f . Ear p innaewere free with the distalpor t ion of the p innae p ig-mented. Only the abdominalmammae in the females werevisible. The Y-shaped skulll ine was completely hiddenby the in tense p igmentat ionand hair development in theskin. Young were able tocrawl with legs splayed andthe abdomen touching thefloor. Eye lids were moreprominent with the swell ingof the eyes. Mi lk in thestomach was st i l l ev ident .The penis of the male wastwice the size of the clitorisin the female. The anogenital distance for the maleaveraged 1.5 mm and was0.9 mm in the female. Theumbilical scar was sti l lev ident .

The dorsal part of the headand body was heavily pig-mented. Pigmentation hadextended to the heel and theanterior surface of the wristregion of the hind feet. Thedorsal part of the hind feethad acquired s l ight p igmen-tation. Pigmentation on thetail was more prominent butno hair had emerged. Shorthair with pigmented basehad emerged around the eyesand the muzzle region. Thegenal vibrissae had acquiredslight pigmentation at thebase. More short f ine un-pigmented hair had grownon the dorsum of the body.

No hair had emerged on theventer except for the threesubmental vibrissae (averagelength of 1.5 mm) and othershort unpigmented hair underthe lower jaw. Venter skinwas slightly darker but milkin the stomach was sti l lvisible. The young were ableto crawl with their bellyslightly off the ground. Thefuture upper inc isorsappeared as two white spotson the gum.

The anterior aspect of theupper hind legs had acquiredpigmentat ion. Pigmentat ionaround the head and ankleregion was darker. Thedorsal part of the tail waspigmented but the ventralpar t was st i l l unpigmented.There was a slight indicationof pigmentation on the dorsalaspect of the front feet. Theupper part of the front legswas sti l l pink. Pigmentedhair had emerged on thedorsal part of head and body.Short, fine, unpigmented hairhad emerged from the dorsalpart of the tail and the frontand h ind legs. Unpigmentedhair of about 1.5 mm rnlength was distinctly visibleon the lateral aspect of thebody. No hair had emergedon the venter. The distalportion of the ear pinnae wasdarker and more pigmentedbut no hair had erupted onthe ear pinnae. The longestmystacial vibrissa averaged4.2 mill imetres. Hair papil laeof the supercil iary, genal andsubmental vibrissae weredistinctly visible. The super-cil iary vibrissae were 2.8 mmin length. Mammae in thefemales were visible (the

Day 6

Day 5

193

Day 7

Day 8

mammae formula was 3+2:10). Milk in the stomachcould be discerned.

Pigmented hair had emergedon the anterior surface of thedorsal part of the hind legsbut not on the dorsal part ofthe feet. The front legs weresti l l dark pink but unpig-mented fine hair had eruptedon the dorsal surface of thefeet. The dorsal part of thetail was covered by blackpigmented hair. The ventralpart of the tail had acquiredshort, unpigmented hair.Hair tracts were distinctlyvisible. The young began tobe active while beingmeasured and t r ied to jump

off the weighing pan. Theywere observed for the firstt ime resting with hind legspulled beneath the body.Crawling was much improvedbut the hind legs were sti l lsl ightly splayed. The youngwere able to l ift their bellyoff the ground when walking.The incisors had not eruptedbut were evident through theupper and lower gums. Thedigital nails of the hind feetwere evident.

Brown hair had began toform on the head andshoulder regions and alongthe sides of the body leavingthe mid-dorsal region withblack and long whi te hai r .More unpigmented shorthai r . measur ing approxi -mately 1 mm, had emergedon the ven te r . Wa lk ing co -ordination was sti l l unsteadybut young were able to turnupright when placed on theirbacks. The incisors had noteruoted. The eves were sti l l

closed but eye slits were verydistinct, measuring 2.8 mmlong. Umbilical scar was sti l lapparent. Sparsely unpig-mented hair had emerged onthe anterior surface of earpinnae. Upper part of thefront legs was sti l l pink.

Silvery hair on the uppersurfaces of both the frontand hind feet were evident.Short pigmented hair wereconspicuous on the dorsalsurface of the front feet.

Young were very active andwere able to run off theweighing pan. Young wereable to run about unsteadily.Brown fur of about 1 mmlong had covered the headand body. The long whitehair were triple the length ofthe brown hair. Light brown-ish hair had emerged on thedorsal surface of the hindfeet. Dark pigmented hairwere evident on the dorsal(back) of the ear pinnae butthe front was sti l l hairless.Hair tracts on the venterwere visible. The upperincisors had began to emergebut had not pierced the gumcompletely. Eves were sti l lclosed and the auditorymeatus st i l l unopened. Mi lkin the stomach was sti l l evi-dent through the venter. Tailwas bicolour, black dorsallyand whi te ventra l ly .

The dorsal pelage was vervwell developed with brownand black hair giving a shinysheen. Venter pelage wasmore dense but milk was sti l lvisible through stomach.Young were able to grip andhang on to a bambclo st ickwrth their front legs. Ear

Day 9

Day 10

194

Day 11

Day 12

Day 13

pinnae were finely furredand the auditory meatus wasbeginning to form. Eyeswere sti l l closed. Themammae were now clearlyd iscernable (3+2:10) . Theumbilical scar was barelyvisible and was surroundedby venter hair. Yellowish-tipped hair were found at thebase of the front of the earpinnae. The young ran aboutunsteadily and the hind legswere sti l l splayed. The upperand lower incisors of themales had penetrated thegums for about 0.5 mm whilethat of the females had iustpenetrated the gums.

The eyes and the auditorymeatus were sti l l closed. Themystacial vibrissae measuredan average of 9 mm and thesupercil iary 7.5 mill imetres.The mean length of hai r onthe dorsum was 3.6 mm andthe venter was one mill i-metre. A midline of slightlyyellowish hair was evidenton the venter. The venterhair were dense and greyishwhite. The young were awareof height and able to sense itby stopping at the edge ofthe measuring table althoughthe eyes were sti l l closed.Gripping abil ity of the youngwas improved as both frontand hind feet were able tohang on to a stick. The upperand lower incisors of thefemales had penetrated thegums completely.

The eyes and the auditorymeatus were still closed.

Auditory meatus hadopened. The initial responseto hearing was observed

(young were startled by thesnapping of f ingers). Earpinnae were covered withbrownish hair.

Eyes were sti l l closed.Young were more adept atclimbing.

Eyes of the young were sti l lclosed but one eye of a malewas half opened. Young hadnormal walking gait l ike theadults. Mammae in thefemales were hidden bygreyish-whi te venter hai r .

The eyes of the young hadopened completely. Theyoung were exceedinglyactive and were more pro-ficient at walking andrunning than before. Whendisturbed, the young werequick to avoid the source ofdisturbance, accompaniedwith squeeking sounds. Facewashing and groomingbehaviour was observed inthe young. The dorsal pelagecomprised brown and blackhair. The basal half of thebrown hair was grey andmeasured 6.2 mill imetres.The long black hair measuredseven mill imetres. Venterhair were greyish white andmeasured 2.5 mill imetres.The longest facial vibrissawas 13.5 mi l l imetres.

The young were observed todrink water from spout. Theeyes were more protruded.

Fight-play interaction amongthe young was observed. Themother was quick to retrievethe young when they tried toventure away from the nest.Lower molars had erupted.

Day 14

Day 15

Day 16

Day l7

195

Day 18

Day 19

Day 20

Day 21

Day 28

Day 35

The young had learned todehusk whole rice grains andthe eating of solid food(laboratory pellets) wasobserved. Upper molars haderupted.

The testes had not des-cended into the scrotum inthe males and vaginae in thefemales were imperforated.

Pelage of the young was softand thick. Dorsal pelage wasthe same as on day 16. Venterhair had grown longer andthe average length was 3.1mill imetres. The tail wasbicolour. The males andfemales were separated atweaning. The mean weightsfor males and females were3.67 g and 3.82 g, whi le theHBLs for males and femaleswere 51.1 mm and 52 mmrespectively. The develop-mental characteristics for thefirst 21 days are summarizedin Table 4.

Testes in the males were sti l labdominal and vaginae inthe females were sti l l imper-forated. Hair on the dorsumwas about 7 mm long and theventer hair was 3.8 mill i-metres. The longest mystacialvibrissa was 17 mill imetres.

The colour of the dorsalpelage was brown and blackwhile the venter was greyishwhi te.

Brown hair on the dorsumaveraged 6.6 mm in lengthand the long black hairaveraged seven mill imetres.The length of venter hai r was4.2 mill imetres. Weight ofthe young ranged between

Table 4. Developmental characteristics ofMus caroli in the first 21 days after birth

Event Age (days)

Appearance of vibrissae

Appearance of pigment on body

Appearancc of unpigmentedbody hair

Ear pinnae unfolded

Appearance of pigmented bodyhair

Appearance of mammae (females)

Separation of digits

Appearance of brown hair

Upper incisors erupted

Lower incisors erupted

First hearing response

Auditory meatus opened

Hair obscured mammae

Eyes opened

Displaced young able tolocate mother

Lower molars erupted

Upper molars erupted

I (<12 hours)

3

4

4

6

6

6

8

1 0 - 1 1

1 0 - 1 1

l - )

1 3

1 5

1 5 - 1 6

1'7

1 8

l 9

Day 49

8.1 g and 9.6 g and the HBLwas between 61 mm and 69mill imetres. The length oft he ea r was 11 -13 mm andthat of the hind foot was 16-17 mill imetres. The length ofthe tail was 1l57o of thehead and body length, with arange of 63-75 mill imetres.

Adult pelage had began toappear along the facial andlateral portions of the body.Testes of the males haddescended into the scrotum.Vaginae of the females weresti l l imperforated. Hair hadobscured the vaginal orif ice.The mystacial vibrissaeaveraged 17.6 mm, wi th ablack basal half and theupper part white.

New coat had completelycovered the dorsum andmoultins into the adult

Day 42

196

Day 56

Day 98

pelage had completed.Vaginae in the female sti l limperforated.

Vaginae in the female werestill not perforated.

Growth Characteristics of M. caroli fromthefirst to 25th week after Birth

Figures 2 and 3 describe the growth ofmale and female M. caroli from first to 21stday after birth. The growth curves of weightand HBL in the first three weeks showedtwo breaks, on the seventh day and theother on the 14th day for both sexes. Theaverage daily increases in weight during thefirst 21 days after birth were 0.13 g for malesand 0.14 g for females. The mean weightsfor males and females at 21 days after birthwere 3.67+0.22 g and 3.82+0.34 g respec-tively. The average daily increases in HBLfor the first 21 days were 1.0 mm for malesand 1.1 mm for females. The mean HBLs ofmales and females at 21 days old were51 .1+0 .9 mm and 52 .0+1 .4 m i l l ime t res .

Body wc igh l

o*",oo" l ' , 14 16 l l r 2{ t 22 '

Figure 2. The relationship between age,weight, and head and body length oflaboratory bred male Mus caroli during the

first 3 weeks after birth (Means from 19males, S.E. of means too small to include in

the growth curves).

^*.,u"rl ' i l '1 16 l l l 20 l l

Figure 3. The relationship between age,weight, and head and body length of labora-tory bred female Mus caroli during the first 3weeks after birth (Means from 12 females,S.E. of means too small to include in the

growth curves).

Growth curves of male and female M.caroli from first to 25th week are given inFigures 4 and 5. Growth rates for weight andHBL were most rapid during the first tofourth week. Weight gains of 1.00 g/weekand 1.03 g/week were recorded for malesand females respectively (Table 5). Increasesin HBL of 6.92 mm/week and 6.87 mm/week were recorded for males and femalesrespectively. From the fifth to eighth week,growth was slower. Weight gains in themales and females were 0.83 g/week and0.58 g/week respectively. Increases in HBLfor the males and females were 2.54 mm/week and 1.96 mm/week respectively (Table5). Growth was very slow from the ninthweek onwards and gains in weight of lessthan 0.5 g/week were recorded for bothsexes. Similarly, increases in HBL were verysmall, less than 1.0 mm/week for both sexes(Table 5).

DISCUSSION

Among the rice field rodents inPeninsular Malaysia, M. caroli is the

-

55I

a

=1 5 c

J

ia

:.s E

33

t )

J

i

3t 5 -

197

20

It i

l 6

1 1

^ 1 - )

C 1 l{ l r'a- 8

6

4

2

9{)

8(

70

60

50

Ec

I 3 s 7 9 l l 1 3 1 5 1 7 1 9 2 1 2 3 2 5Agc (wec l i s . )

Figure 4. Growth curves of male Mus caroli from Ist to 25th week in the laboratory.

Age (wccKs )

Figure 5. Growth curves of female Mus caroli from Ist to 25th week in the laboratory.

'nrI

l 6 l -I

r 1l-I

. - l- l , l -

I:- toF

I

I. lnr

II F

I- l

I( ) L

aeF

Body ueight

Tai l lc-ngth

Head & bod.v length

Hincl foot length

Bodv wcight

90

It0

70

60

50

40

Tai l lcngth

Hind foot length

1 3 5 7 9 l l 1 3 1 5 1 7 1 9 2 1 2 3 2 5

198

Tabfe 5. Growth rates of Mus caroli from1st to 25th week after birth

Age(weeks)

Wt. gain (g/week) Increase in HBL (mm/week)

Male FemaleMale Female

1-4

5-8

9-12

t3-25

r .000.830.49

0.48

6.921 < ^

0.82

0.48

1.03

0.58

0.46

0.43

6.8'7

1 . 9 6

0.7 |

0 .29

smallest member. Adult mice hardly reach aweight of 20 g and HBL of 90 mm(LnNcueu and LAM, 1911). Being thesmallest member, it also has the lowest birthweight. At birth, the young weighed onlyabout one gramme. The common rice fieldrat, Rattus argentiventer (RoelNsoN &Kt-oss) has birth weights of 3.9 g and 3.6 gfor males and females respectively (Lnn,1979). Mean litter size of M. caroli was 4.3,with a range of two to seven. For wild M.caroli females, a range in litter sizes of threeto eight had been recorded (LaNcunv andLev 1977).It is l ikely that captive M. carolifemales have slightly smaller mean litter sizecompared with those of the wild females.This lower mean litter size for zoo femaleswere similarly observed in two other ricerodents in captivity, R. argentiventer (Lert,1980; 1983) and Bandicota indica (Lnv,1e8s).

Two breaks were observed in thegrowth curves of body weight and HBL ofM. caroli during the first three weeks afterbirth. Scudder, Knnczvan and LocrErr(1967) reported two similar breaks for thehouse mouse, Mus mu,sculus Linnaeus.ENzntaNN (1933) reported that in M.musculus these breaks were due to changesin the maternal milk supply, where thequantity of milk increased rapidly up to thefifth day after parturit ion, increased veryslightly further up to the 12th day, anddeclined rapidly thereafter. This samemechanism is thought to account for thechanges in the growth of M. caroli. Thesecond break correlated with the opening ofthe eyes and an acceleration in body weightgain suggested an increase in the consump-tion of solid food. The young were observed

to dehusk and consume rice grains two daysaf ter the eyes opened.

Wrr-lrevs and Scorr (1953) dividedgrowth and behavioural development of M.musculus into four distinct natural periods:(a) the neonatal period during which deve-lopment is mainly in growth and strength,with the appearance of very few overtbehavioural patterns not present at birth,(b) the transitional period, marks bychanges in sensory and motor capacitieswhich make possible the development ofadult behaviour patterns, (c) the socializa-tion period which begins with the opening ofthe eyes and includes the first extensiveactivity outside the nest, and ends with finalweaning, and (d) the juvenile period, inwhich all behaviour is essentially adult withthe exception of sexual behaviour and careof the young. The period extends fromweaning to sexual maturity. For M. caroli,these periods could be defined as follows:neonata l (1-8 days) , t ransi t ional (9-15days), socialization (16-21 days) andjuvenile (22 days to sexual maturity).

The neonatal period is a crit ical t imefor survival in the young and is characterizedby neonatal nutrit ion and rapid growth(Wrr-lrnvs and Scorr, 1953). Deaths oftenresult from failure to compete for maternalcare and nursing or the cannibalism by adultfemales. There were numerous instances ofcomplete loss of l i tters due to cannibalismby the dam. Mus caroli is very sensitive todisturbances of the nest and cannibalismusually occurred when the brood wasdisturbed during the course of examinationand measurement. Cannibalism of theyoung by adult females was also common

t99

during the neonatal Period in R.

argentiventer and R. tiomanicus but

uncommon in B. indica (Lau, 1985).

In rodents, it has been generallYaccepted that the testes descend into the

scrotum as the male becomes sexuallymature and the vaginal orifice becomesperforated as the female approachesmaturity. Sexual maturity in male M. caroliwas attained in an early age of less than twomonths. Males had scrotal testes at the ageof 49 days but the vaginae of females of the

same age were still imperforated. Themoulting into adult pelage had began at 49

days and this was completed at 56 days of

age. Female mice, M. musculus, becomesexually mature at around six weeks andlater under unfavourable conditions(Cnowcnonr and RowE, 1957; 1958;Ba.nNet.r and ColEveN, 1959). Males attainpuberty later than females but are less

affected by environmental fluctuations(Bennv, 1970). Thus, it is l ikely that M.

caroli females would be sexually mature atabout two months of aqe under normalconditions.

Vaginae of female M. caroli were stillimperforate when they were examined at 98days of age. This could be due to thephysical separation of the sexes at weaningand they were kept separated throughoutthe study. Female mice (M. musculus) were

known to require chemical cues (priming

pheromones) for ovulation and induction ofpuberty in young mature females (BnoNsott

and CoouEr-rru, 1980). In mice, both sexesmark their home substrate with urinarypheromones. Urinary cues emanating frommales accelerate the process of ovulationand urinary cues from females decelerate it

(BnoNsoN and Coeur,l lN, 1980). It has also

been shown indirectly that the exposure of

immature females to an adult male would

result in precocial vaginal opening and

mating (VeNnr,NsERcH, 1967.VRNoENsEncH, Dntcxnnae,R and Cot-sv,1912). The precise cue involved in theinduction of precocial puberty is probablypheromonal in nature (VaNneNeencH,1969). In deermice, females show oestrusinfrequently when caged in groups in amale-free environment. Incidence of oestrusis increased, in some cases more than twofolds, following exposure to the presence ofa deermouse male or to his urine (BnoNsoN

and DBzr,ll, 1968). The above phenomenonprobably explains the delay in puberty(perforated vagina) of females M. caroli,due to its isolation from the pheromonalcues of males.

The sex ratio of young born in thelaboratory was greatly in favour of males,

t.e., about twice as many males were born.This reproductive strategy would facilitatethe sexual development of the females in thewild. The large number of males produced

would increase the chances of femalesmeeting males which is a prerequisite for theinduction of puberty in females, thusensuring the reproductive success andsurvival of this species.

ACKNOWLEDGEMENTS

The author is grateful to the Director,Rice Division for permission to publish thispaper, the late Mr Thong Chin Poh for

technical assistance, Mr Yap Beng Ho for

statistical analyses, Mr Lee Ah Kaw for his

help in the i l lustrations and Ms MahaniMaulud for typing the manuscript.

ABSTRACT

Post-natal growth and development of Mus caroli ware studied for litters born in the laboratory.

Detailed observations on the growth and morphological development were made and the physical

development of the young was described. Litter size of captive females varied from two to seven, with a

mean of 4.3+0.4. Mean bir th weights for males and females were 1.02+0.02 g and 0.96+0.02 g

respectively. The total birth weight of litters varied between 14.5Vo and 16.4o/a of the weight of the dam,

wit'h a mean of 30.0+2.6 per cent. Sex ratio in the litters was markedly in favour of males, with a ratio of

2.2:7. ' lhe post-natal development of M. carol i can be div ided into four phases: neonatal (1-8 days),

transitional (9-15 days), socialization (16-21 days) and juvenile (22 days to sexual maturity).

200

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REFERENCES

Accepted for publication on 25 October 1986

20r

Dicetak oleh Unit Percetakan MARDI, Serdang, Selangor.Kementerian Pertanian Malaysia.