1 '~; c\ 1.Introduction

Transcription

1 CHAPTER - H

2 1 '~; c\ REPRODUCTIVE BEHAVIOUR OP GERBILS V RETRIEVAL OP YOUN& 1Intrductin 'Retrieval 1 r carriage f straying r fallen yung t the nest by 1actating mthers, frms an Imprtant cmpnent f the maternal behaviur f labratry rat, Rattus nrvegicus (Beach and Jaynes,1956a, 1956b, 1956c; Rsenblatt and Lehrman, 1963; Barnett, 1975) Ensuring better survival f the yung, it is a steretyped pattern under multi-sensry cntrl (Barnett, 1975) Females f the wild type, R nrvegicus Berkenhut, have als retrieving abilities (Barnett, 1975); and the behaviur has als been bserved in the desert gerbil, Merines hurrianae (Jerdn) (Mnthana, 1975) It has, hwever, nt been studied and timed under standard cnditins Such abilities are cnsistent with the high quality f maternal care that female rdents prvide t their yung The Indian gerbil, Tatera indie a indie a (Hardwicke), is n exceptin In this regard Results f experiments designed t study * retrieving f yung* by their lactating females are discussed here

3 lu 2 Material and Methds 21 The Subjects: Subjects were wild-caught stck, maintained n rat diet (Hindustan Lever Ltd) and ad lib water Selected adults were weighed and gruped int bisexual pairs; and transferred t wire-mesh cages, i32 x io x 0,32 m, prvided with wden nest bxes, 20 x 105 x 9 cm, and newsprint strips, 30 x 30 era, fr nesting Sand was given in separate trays fr «bathing Arrangements made inside the cages* are shwn in Fig26 The gerbils were left undisturbed fr the next 20 days, but then the cages were examined daily The males were remved when a litter, brn bviusly in the prceeding night, was detected Of the 4 females tested in expt i, Nl f 125 g bdyweight had a litter f 2 yung, N2 f 168 g f 3 yung, N3 f 152 g f 4; but N4 f 125 g weight had als 3 yung in it's litter Females N5 and6included in Expt2, were als suckling respectively, 2 and 3 yung 22 Experimental Prcedure? Observatins began 12 t 24 hrs after parturitin, ie n the same day that a litter was detected, r later when the pups were 11 days ld Mther gerbils were remved frm the cages between 1600 t 1800 hrsj and released back after the yung had been marked, weighed and placed in the sand trays Frceps biled in water and dried with sterilised twels, were used fr handling them

4 Figure 26 Arrangements inside test cages, shwing the psitins f nest DOX (N), fd tray (P), water dish (W) and, sand tray (S) in which the yung were ffered fr retrieval

5 i V -,* u, Fig 26

6 182 Fllwing re-entry f mthers int the cages, an bserver (li) made the lwing bservatins: (i) Latency, in secnds, with which the first pup f the litter was retrieved, r carried frm sand tray t the nest bx It was timed frm the entry f mther int the nest bx t the mment, when after cming ut, it seized the first pup, (2) Latencies, in secnds, with which the ther pups in the litter were retrieved, r the interval between the entry f mther int the nest bx with ne pup and the seizure f the next when it came ut (3) Regin f bdy n which the pups were seized (4) Time, in secnds, spent by mthers in searching the cage after retrieval f all pups in the litter This test was repeated in Expt 1, each day frm birth, r after the age f ii days, t weaning Respnses f lactating gerbils t plastcene mdels f their pups placed in the sand trays, were bserved in Expt, 2 2,3 Analysis f Results: Methds described by Bailey (1959) were lwed fr calculating means, standard deviatins, standard errrs f the means (SE), and fr cmparing retrieval latencies* Cmparisns were made by paired t 1 tests

7 1 3 Results The results are summarised in Tables 23 t 25 and illustrated in Pigs 20 and 28 It wuld appear that bservatins n nly tw litters culd be cmpleted frm birth t weaning (Table 23) Female N 3 died 13 days after parturitin fr unknwn reasns; while retrievals by female N 4 were timed nly after the lith day < 31 Grwth f Gerbils frm birth t Weaning: The gerbil pups at birth were fund blind, naked; and with limited rientatin reexes They were, hwever, able t prduce audible signals (r 'squeaking' ) Their bdy-weight varied frm 4 t 5 g (mean = SE 002 g) It increased at the rate f SE 032 g/day Orientatin reexes were, hwever, rapidly acquired; crawling mvements began at the age f 5 days, and the pups started walking at the age f 13 days The eyes pened at 18 days; by which time mst f the fur had als develped Weaning ccurred at 28 days after parturitin Experiment 1 32 Retrieval f yung: The yung were retrieved by their mthers, frm birth t the age f 22 days (Figs 2<J and 2$) On the remaining days befre weaning, they reached the nests withut their help Later they mved freely, but spent little time in the nest bxes

8 Figure 27 Latencies, la secnds, with which tbe pups were retrieved by female H, 2

9 i N 2, 5 = 1689 Fig 27

10 \ Plgnre 28 Latencies fr retrieval f pups ia anther example, f female N, i

11 1^5 i i i i MI i i ii Days Pig 28 20

12 lrfg The lactating- gerbils shwed bvius signs f distress when remved frm the cage, r deprived f cntact with their yung less than 22 days in age On being released back int cages, they first rushed t and lcked fr them in the nest bxeg Cming ut after variable perids, they reared and backed abut the nests befre mving arund Aided perhaps by squeaking f pups, they walked acrss t sand-trays Retrievals began sn after; as the pups were lifted ne by ne and carried int the nest bxes Only nce, n the 11th day after parturitin, female N3 attempted t build a new nest where it was ffered the pups, ie in the sand trays Retrieval ccurred n the run; and n successive runs, a straight curse t the nest bx was lwed The pups were nt nursed r licked in the meantime The cages were als searched fr variable perids after retrieving all the pups (Table 23) 33 trips' used r the methd f retrieval? The gerbils used different grips in lifting the pups When 1 t 10 days in age, the pups were caught n the abdmen, exactly n the ank, by * the teeth; t which they als respnded by curving in their bdies* Pra the age f ii t 15 days, they were lifted by nape f neck; and then t age f 22 days by skin n their back The neck grip was, hwever, repeated by female N2 n 22 day ld pups

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14 Latencies fr retrieval f pups: Latencies fr retrieval f pups, hwever, did nt vary with their age (crrelatin test, P> Oi), In respect f all the pups, thugh with different mthers, it uctuated, rather alternatively, n successive days after parturitin (Pigs, 26f and 2$) The range f variatin was, hwever, wider in case f the latencies timed fr the retrieval f fist pup than the latencies with which the remaining pups f the litter were retrieved (Table 23) Generally thus, 10 t 120 secnds (0,166 t 20 minutes) elapsed befre the first pup was retrieved; 10 t 105 secnds (0,166 t 1,75 minutes) befre that f the secnd; 10 t 60 secnds (016 t 1,0 minutes) prir t the carriage f third pup, while an interval f nly 20 t 60 (0,3 1,0 minute), in the nly example f female N,3, ccurred when the furth pup was seized and carried int the nest Differences nted in latencies were, hwever, fund significant in mst instances (Table 24), Within the litters similarly, a linear rder in retrieval latencies was discernible (Pigs, 2Q and 2%), Thus, retrievals ccurred, ne after the ther, at shrter intervals f time; thugh again the differences seemed mstly significant (Table 25) Ttals f latencies shw that female N,3 with 4 pups, spent the maximum time in retrieving, lwed by female N, 2 and 4, each with 3 yung, while female Nl with a litter f 2 pups, spent the minimum time (Table 23)

15 Table - 24 Paired 't* values fund by cmparing the latencies with which the pups were retrieved by gerbils f experiment i t' f latencies timed ff retrieval f 1st pup 2nd pup 3rd pup Females Nl and 2 312* 540* Females Ni and 3 251* 399* Females Nl and 4 265* 144 Females N2 and 3 317* * Females N,2 and 4 365* i95 Females N3 and 4 - * Significant, P< 005

16 140 Table - 25 Paired 't* values shwing the relatinship between the latencies bserved fr retrieval f pups f the same litter, Female f t f f latencies fr retrieval f i Pup Pup Pup Pup Pup Pup 1 and 2 1 and 3 1 and 4 1 and 3 1 and 4 3 and * 2 396* 3 230* 4 240* 339* - 273* * i99 246* 264* i85-260* Significant, P< 005

17 141 Experiment 2 35, Respnses t mdels f pupss Lactating gerbils ignred the plastcene mdels f pups presented t them Hwever, what was made as 'eyes' in the mdels, was fund chewed n mst ccasi ns 4 Discussin Retrieving is an experimentally induced respnse (Rsenblatt and Lehrman, 1963); and it's relevance t wild rdents while living in their natural surrundings, is suspected (Barnett, 1975) Thus, it may nly he a variatin f the prcess f transprt f pups t new nests, as ccasinally bserved there (King, 1963; Barnett, 1975) Of the gerbils tested in expt 1, female N 3 als tried t build a new nest in the sand trays, befre transprting the pups t the riginal nest several hurs later Hwever, there are reasns t believe that it is a separate cmpnent f maternal behaviur; and that it has survival value Retrieving abilities may thus help the lactating gerbils t (l) prevent the yung frm falling ut f the nest, when they begin crawling at the age f 5 days, (2) stp them frm straying nce they start walking at the age f 13 days and (3) in bringing them back t nest lwing a chance rescue frm a predatr, as bserved in an allied species by Muthana (1975)

18 14^ Perhaps fr these reasns, the behaviur never waned in»ur gerhils fr 22 days lwing parturitin; whereas in the dmesticated labratry,rat, it begins t dissipate after 10 t 16 days f it (Rsenblatt and Lehrman, 1963) Althugh the litter size varied, it lasted nly 2 t 5 minutes, with latencies fr retrieval f successive pups decreasing in a linear rder (Table 23; Pigs 2$ and 2%) Cnversely in the white rat, lder pups are retrieved after lng delays (Rsenblatt and Lehrman, 1963) Similarly, latencies with which the first pups were retrieved by gerbils, differed nly slightly (Table 23; Pigs 2 and 2$) There was, hwever, little chance f their retrieving abilities having imprved with practice, as bserved in several Investigatins n the labratry rat (Barnett, 1975) Thus, retrieval latencies shwed significant differences at equivalent ages f pups (Table 24); even thugh tests n female N4 began late, r 10 days after parturitin (Table 23) Retrieving stpped when the yung began t resist it; and tried t reach the nests n their wn The lactating labratry rats n the cntrary, themselves grw less attentive as the pups grw lder The difference reects the strnger develpment f the behaviur in a wild species, cmpared t it's lss with dmesticatin in the latter

19 14 The methd f lifting the yung r 'grip' used, hwever, have nt changed with it Like the labratry rats, lactating gerhils als prtect the head and drsal side f pups frm rubbing the surface ver which they are carried The results f expt 2 clearly shw that retrieving is nt simulated by bjects resembling the pups in size and shape* That such bjects aruse the curisity f gerbil mthers, is, hwever, bvius frm the chewing f nly the 'eye' in the mdels It is likely that the head is investigated mre than ther parts f the pup's bdy Summary Lactating gerbils, Tatera indica indica (Hardwicke), retrieved their yung, ne by ne, t the nests when the litters were displaced t psitins away frm it The behaviur lasted fr 22 days after parturitin, but latencies fr retrievals did nt change with the grwth f pups Hwever, the 'grip' used in retrieving varied with their age; pups were seized by teeth n the ank, by nape f the neck and skin n their back, in the rder named Mdels f pups presented t mthers were, hwever, ignred in anther experiment