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Gerbils fostered to rat mothers : effects on adult behavior Bols, Rosemary Jean 1973

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GERBILS FOSTERED TO BAT MOTHERS: EF23CTS ON ADULT BEBAYIOR by ROSARY JEAN BQLS B.A., Honour3, University of British. Columbia, 1971 A THESIS SUBMITTED IN PARTIAL BPLFTJMKNT OF TBS REQUIREMENTS FOR THE DBJR33 OF MASTER OF ARTS in the Department of Psychology We accept this thesis as conforming to the required standard The University of B r i t i s h Columbia A p r i l , 1973 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia Vancouver 8, Canada Date ABSTRACT At 72 brs after birth gerbll l i t t e r s were divided and half the pups fostered to lactating mot bar rats whose own pups ware removed* Remaining pups were returned to their natural mothers- Rat-reared gerbils had a higher mortality rate than control gerbils but weighed more at weaning. At 60 days control gerbils weighed more and at 100 days there was no difference i n weight • When tested in the open-field from Day 128 to Day 135, rat-reared gerbils were found to loco mote and rear less than control subjects. Share was no difference in defecation or in the tendency to enter the central squares as a result of foster-ing. The paper shredding and t e r r i t o r i a l marking activity of the subjects were also measured but no clear cut effects of fostering emerged on these tests. The results were discussed in relation to those obtained with, rat-reared mice and i t was suggested that species differences i n maternal behavior, especially handling and retrieving of pups, may be the crucial factor responsible for fostering effects« TABLE OF CONTENTS PAGE Abstract i i Table of Contents i i i Li s t of Tables • i v L i s t of Figures '. I I v i Acknowledgement Introduction • • • -j. Matnod • • • • • • • • • • 10 Subjects 1 0 Apparatus • 10 Procedure • • • » • 10 Results 2.G Discussion • • • 55 Conclusions • • • 65 LIST OF TABLES TABLS PAGE 1* The Number of Subjects Born, Assignment to Conditions, and Survival Rate within each L i t t e r 12 Z' Means of 23 Day Weight • 18 3« Means of 60 Day Weight l8 4» Means of 100 Day Weight 18 5. Summary of Analysis of Variance of 23 Day Weight: Treatment • 20 6* Summary of Analysis of Variance of 23 Day Weight: Cage Type within Group RR 20 7* Summary of Analysis of Variance of 60 Day Weight: Treatment . . . . . . . . . . . . . . . . 21 8» Summary of Analysis of Variance of 60 Day Weight: Cage Type within Group RR 21 9* Summary of Analysis of Variance of 100 Day Weight: Treatment 22 10* Summary of Analysis of Variance of 100 Day Weight: Cage Type within Group RR 22 11* Summary of Analysis of Variance of Total Squares: Treatment • 25 12. Summary of Analysis of Variance of Total Squares: Cage Type within Group RR • 25 13. Summary of Analysis of Variance of Rears: Treatment 29 14» Summary of Analysis of Variance of Rears: Cage Effect within Group RR 29 15• Summary of Analysis of Variance of Center Time: Treatment 32 16* Summary of Analysis of Variance of Center Time: Cage Type within Group RR • 32 17* Summary of Analysis of Variance of Thigmotactic Ratio: Treatment • 36 18* Summary of Analysis of Variance of Thigmotactic Ratio: Cage Type within Group RR • • • • 36 V TABLE PAGE 19* Summary of Analysis of Variance of Open-field B o l l : Treatment ko 20* Summary of Analysis of Variance of Open-field Bol i : Cage Type within Group BB • 4-0-21 • Summary of Analysis of Variance of Paper Shredded: Treatment • 22* Summary of Analysis of Variance of Paper Shredded: Cage Type within Group BB hz 23* Summary of Analysis of Variance of T e r r i t o r i a l Mar Icing: Treatment k6 24* Summary of Analysis of Variance of T e r r i t o r i a l Marking: Cage Type within Group BR *+6 25* Summary of Analysis of Variance of Defecation in the Marking Apparatus: Treatment hS 26* Summary of Analysis of Variance of Defecation in the Marking Apparatus: Cage Typa within Group BR 49 27* Means of Ventral Gland Size 51 28* Summary of Analysis of Variance of Ventral Gland Size: Treatment "~ 52 29» Summary of Analysis of Variance of Ventral Gland Size: Cage Type within Group BR 52 30* Number of Pairs which Fought 53 31* Means of Fighting Latencies 53 32* Suamary of Analysis of Variance of Latency to Fight: Treatment • • 53 33* Correlations between Behaviors • 5^ LIST OF FIGURES FIGURE PAGE 1. Mean number of squares entered during 5=min open-field tests by control males, control females, rat-reared males, and rat-reared females • 23 2* Mean number of squares entered during 5-min open-field tests by rat-reared gerbils raised i n metal and plastic cages • • 2k 3. Mean number of rears during 5-min open-field tests by control males, control females, rat-reared males, and rat-reared females • . 27 4. Mean number of rears during 5-min open-field tests by r a t -reared gerbils raised i n plastic and natal cages 28 5. Mean number of seconds spent in the central area of the open-f i e l d on each 5-min test by control males, control females, rat-reared males and rat-reared females 30 6* Mean number of seconds spent i n the central area of the open-f i e l d on each 5-min test by rat-reared gerbils raised i n metal and plas t i c cages 31 7* Mean thigmotaotic r a t i o of control males, control foca le s , r a t -reared males, and rat-reared females during 5-min open-field tests* • • . . 3^ 8* Mean thigmotactic r a t i o of rat-reared gerbils raised i n metal and plastic cages during 5-min open-field tests* 35 9• Mean number of b o l i deposited on each 5-min open-field test by control males, control females, rat-reared males, and r a t -reared females* • • • • * 38 v i i FIGUB3 PAGE 10* Mean number of b o l i deposited on each 5-min open-field test by rat-reared gerbils raised in metal and plastic cages • • 39 11* Mean number of grams cf paper shredded during 2*5-hr tests by control males, control females, rat-reared males, and rat-reared females ^1 12» Mean number of grams of paper shredded during 2«5-hr tests by rat-reared gerbils raised i n metal aM plas t i c cages. . . . 13. Mean number of ventral marking responses performed in appar-atus on each 5-min test by control males, control females, rat-reared males, and rat-reared females. * 1+1+ 14* Mean number of ventral marking responses performed in appar-atus on each 5-min test by rat-reared gerbils raised i n metal and plas t i c cages ^5 15* Mean number of b o l i deposited during 5-min tests i n the mark-ing apparatus by control males, control females, rat-reared males, and rat-reared females. • 47 16° Mean number of b o l i deposited during 5-min tests i n the mark-ing apparatus by rat-reared gerbils raised i n metal and plastic cages* • 3^ Acknowledgement I would l i k e to thank Dr. Roderick Wong for his advise and support and Dr. Fred P. V a l l e for advise and the use of his laboratory f a c i l i t i e s . I would also l i k e to thank Dora Bols for typing and l a s t l y I would l i k e to express my appreciation of the g e r b i l s who showed remarkable gentleness and tolerance throughout the experiments. A number of treatments, when imposed on infant rodents during the preweaning period of development have been found to modify certain be-havioral and physiological characteristics of the adult organism- Such treatments include handling, shock, and hypothermia' There i s some controversy, however, as to the manner in which inese variables exert their effect* Recent evidence suggests that their effects are extremely complex and may be mediated by altering the mother's behavior towards her offspring as well as through direct action on the offspring themselves (Hidgens, Chilgren, and Palardy, 1972). Early experience studies are now beginning to concentrate on the mother and bar interactions with the young as important variables mediating the handling phenomenon and similar effects* One approach to studying the maternal influence on later behavior is the method of cross-postering, l*e«, fostering one species or strain to another. By this procedure, one can begin to separate the genetic-prenatal contributions to behavioral variance from the postnatal maternal factors* In tim normal development of the young animal these factors are usually confounded. If animals which are cross-fostered exhibit behaviors which di f f e r significantly from those of control anitoals, we can conclude that such behaviors are affected by the nature of the postparturient environment (Denenberg, 1970). By directly manipulating the mother-infant relationship and analyzing the maternal behavior patterns which affect the offspring's performance, we may soon be i n a position to isolate the c r i t i c a l aspects of motherhood. The majority of cross-fostering studies have involved the mouse, Mas musculus, as the fostered species and the r a t , Rattus norve^icus as the foster mother species. U'or the purposes of the present paper, 2 the term "fostering treatment" w i l l refer exclusively to fostering to a rat mother, and following Denenberg (1970), the term "fostering effect" w i l l refer to the rather consistent pattern of results obtained from C57BL/10J mice fostered to rat mothers. Denenberg, Hudgens, and Zarrow (1964) f i r s t reported that mouse pups which had been fostered to a lactating mother rat displayed behavioral characteristics i n adulthood which differed markedly from those of mice reared by their natural mothers. Rat-reared mice were found to be less active i n an open-field, to prefer a r a t to a mouse on a two choice social test, and to show a lower incidence of fighting compared to mouse-reared controls. In subsequent studies, Denenberg and his co-workers have attempted to narrow down the range of possible variables that could be responsible for the fostering effect as well as extending the number of dependent measures employed. Apparently fostering per se is not important since i n studies where this variable has been controlled, i.e., where mouse pups are fostered to a mouse mother, i t was found to be without effect (Hudgens, Denenberg, and Zarrow, 1967). In order to eliminate the possibility that observed differences between rat-reared and mouse-reared mice are due to biochemical differences between rat and mouse milk, Denenberg, Rosenberg, Paschke, and Zarrow (1969) developed a r a t "aunt" preparation. This was a nonpregnant, nonlactating female that had f i r s t been primed by exposure to a rat mother and her pups for six days. It was then placed In a cage with a mouse mother and her pups. As expected such aunts behaved maternally towards the mouse offspring, nest "building, retrieving, and hovering above them* It was found that mice tended by rat aunts had a significantly loser cor t i coster one response 3 to novel stimulation, thereby confirming an earlier result but with the milk factor controlled* Although these mice were also less active i n the open-field than control mice, this difference was not significant' It therefore appears that the r a t aunt preparation has a similar, although somewhat lass potent effect to the true foster rat mot her • Since the milk factor did not appear to be the primary variable responsible for the fostering effect, Denenberg, Paschke, Zarrow, and Rosenberg (1969) investigated the p o s s i b i l i t y that the effect was mediated by noncontact stimulation including vision, olfaction, and audition* The only dependent measure taken in this study was the plasma corticosterone response to a novel stimulus since previous studies had shown this measure to be most sensitive to the fostering treatment* Experimental mice were placed with their own. mothers in a cage separated from an adult female nonlactating r a t by a double mesh partition, so presumably they could see, hear, and snail the rat, but no physical contact was possible' Control mice were reared similarly i n the presence of an adult nonlactating female mouse* At the time of weaning the plasma corticosterone response was found to be identical, thus indireotly sup-porting the hypothesis that actual physical contact between the rat mother and the mouse pups is necessary to mediate the observed physiological changes in the mouse• The role of physical contact was observed somewhat more di r e c t l y by Rosenberg, Denenberg, and Zarrow (1970)* They used two types of rat aunt preparation tkat differed in the amount of maternal behavior they ex-hibited* One was similar to the type described previously with the addition that their nipples were t haleeternized* The second type were adult female thalectomized r a t s who had just given birth to their own young. Thus neither type could give milk. The r a t aunts were placed with mouse mothers and their l i t t e r s and their maternal behavior was rated twice daily on a seven-point scale from Day 5 through Day 20. 23ie post par turn rat aunt preparation was found to result i n a greater degree of maternal interaction with pups compared to control aunts. In addition, the open-f i e l d a c t i v i t y and plasma corticosteroid response of the pups reared by these two types of aunts were compared tilth, each other and with a group of pups raised by mouse mothers. The open-field activity of the post partum aunt group was found to be greatly reduced compared to the two control groups. The adrenal response to novelty was also found to d i f f e r among the three groups. The control group gave the greatest response, the control aunt group gave a lesser response, and the post partum aunt group gave the lowest response but the only significant difference was between the two extras© groups. In ad-dition to the between-group comparisons, wi thin-group correlations were calculated. A significant negative relationship was obtained between maternal ratings and corticosteroid level after exposure t a a novel stim-ulus although, correlations between maternal ratings and activity scores were small and nonsignificant. In view of these findings, i t is interesting to note that physical contact between the mother and pups has also been implicated as an import-ant mediator of the handling phenonsn. B e l l , Nitschke, Gerry, and Zaehman (1971) found that whan neonatal pups of the species, PeromyscuB maniculatus  bairdi were handled for 3 minutes, they differed from nonhendJed pups i n the average number of ultrasonic vocalizations emitted. In another study using rat pups, B e l l , Nitschke, B e l l , ant Zaehman ( i n press) correlated ultrasonic vocalization produced by cold exposure with increased maternal retrieving and grooming* These data strongly suggest that handling pups results in modified maternal behavior which, may be responsible fee later changes in offspring behavior* An analysis of infant vocalization and E&tercel behavior associated with cross-fostering has not been carried out but the la t t e r studies suggest the possibility of similar mechanisms operating i n both cases* A l l studies of rat-reared mice conducted i n Denenberg*s laboratory used the C57BL/10J strain wife the exception of one by Paschke, Denenberg* and Zarrow (1971) which compared the effects of the fostering treatment on Swiss albino and C57BL/10J mice* They found that the effect of the treat-ment was similar on some measures but differed on others as a function of strain* The treatment by strain interaction was most pronounced on the fighting measure* A reduced incidence of fighting in C57BL/10J mice reared by rats i s one of the most consistent findings obtained i n these fostering studies yet fostering Swiss albino mice to r a t mothers has no detectable effect on their aggressive behavior* Souths! ck (1968) employed a reciprocal eross-fostering procedure with two inbred strains of mice that differed i n their level of aggression* lie found that fostering males of the passive strain (A/T) to mothers of the aggressive strain (CtfW) significantly increased their aggression over that of controls whereas fostering to A/T mothers did: not reduce the aggression of CM males. Southwick*s study demonstrates maternal influence on the development of aggression i n A/T mice but the kinds of conclusions one can draw from his study (or any study involving a reciprocal cross) are not the same as one can draw from situations where the strain of the mother is constant and the strain or species of fostered offspring i s varied, e.g., Paschke, 6 Denenberg, and Zarrow ( 1 9 7 1 ) * However, because pups of different strains may differ in certain stimulus characteristics, the foster mother might respond differently to pups of one strain than she would to pups of another* Ressler ( 1 9 6 2 ) has presented evidence that the strain of pups does, i n fact, influence maternal behavior* He found that BALB/O pupa received more handling from both BALB/C mothers and C57BL/10 mothers than did C57BL/10 pupa* Hudgens, Denenberg, and Zarrow ( 1 9 6 7 ) studied the open-field activity of r a t mothers as a function of species reared* For mothers which had reared r a t pups, activity decreased over the f i r s t four days following weaning, while the activity of mothers rearing mouse pups increased over the same period* Thus,, not only is the mother an important variable i n determining the behavior of tie pups, but the pups influance the behavior of the mother as well* When attempting to interpret the results of cross-fostering, i t therefore seems necessary to consider the dynamic nature of the mother-infant relationship. In the present study gerbil pups were fostered fc© r a t mothers and the effects of the treatment on the gerbils 1 adult behavior were measured* There were reasons for choosing the gerbil other than simply to extend the generality of the fostering effect to a different species* F i r s t l y , the mouse and the gerbil are known to diff e r physiologically in a number of ways, most notably i n regard to adrenocortical function* The Mongolian gerbil i s a desert animal and can manufacture a l l i t s water requirements from i t s s o l i d food diet and concentrate i t s urine to a marked degree (Cortea and Peron, 1 9 6 3 ) * Furthermore, biochemical analysis of the steroids found i n adrenal venous blood of gerbils shows that 1 9 -hydroxydeoxycorticosterone constitutes one of the major adrenocortical 7 secretions whereas corticosteroid is found in barely detectable amounts (Oliver and Peron, 1964). In the mouse adrenocortical reactivity to a novel situation, as measured by plasma corticosteroid level, has been found to be sensitive to the fostering treatment, rat-reared mice ex-hibiting a reduced response compared to controls (Denenberg, Rosenberg, Paschke, and Zarrow, 1969)* It is possible that this alteration i n adrenocortical reactivity may underlie certain behavioral alterations produced by fostering. Therefore the effect of fostering gerbils to rats would be of interest* Secondly, gerbils exhibit a variety of behaviors f&lca might prove sensitive to the fostering treatment but, because of their species-specificity, have not been possible to investigate i n mice. These include shredding of paper and t e r r i t o r i a l marking* The function of paper shredding i s unknown* I t may have some function i n nest-building but gerbils i n the laboratory w i l l shred paper i n exoess of that required to construct a nest* They also engage i n most vigorous paper-shredding when seemingly excited or disturbed. In support of this casual observation is the finding that gerbils paper-shred immediately after mild foot-shock (Dunham, 1971)» Although paper-shredding i s a poorly understood behavior, i t may be related to other forms of ac t i v i t y such as locomotion and may therefore be sensitive to the fostering treatment* Terr i t o r i a l marking, on the other hand, has toon thoroughly invest-igated and i t s basis is f a i r l y well understood* Both males and females rub a ventral sebaceous gland over low lying objects, males marking approximately twice as frequently as females* This difference corresponds roughly to the sex difference i n gland size (Thiessen, 1968)* A variety of evidence suggests that marking i s androgen dependent and that marking frequency as 8 well as gland size r e f l e c t s the t i t r e of androgen* Castration i n males almost eliminates marking; the gland undergoes a parallel reduction i n size (Thiessen, Friend, and Lindzey, 1968). However, the marking response i s restored by testosterone propionate and the extent of response recovery i s directly proportional to the amount of hormone administered. In gona-dally intact males marking frequency correlates positively with both gland size, (r=«2S), (Thiessen, 1968) and seminal vesicle weight, (r=*54), Blum and Thiessen, 1971)* Although marking appears to be androgen dependent, i t is clear that marking w i l l not occur unless evoked by the appropriate environmental stimuli. Baran and Gliokman (1970) showed that olfactory bulb removal completely eliminates marking and testing animals i n the dark significantly reduces i t . Thus, olfactory, visual, and probably tactual cues play a role in e l i c i t i n g and maintaining ventral marking-A variety of indirect evidence suggests that the function of ventral marking i s , i n fact, t e r r i t o r i a l . Thiessen, Owen, and Lindzey (1971) found that males with the highest narking frequencies usually emerge as dominant individuals i n paired fighting encounters. However, prior know-ledge of marking scores is not a perfect predictor of success i n compe-t i t i o n , (r =-44, p >• 01), since marking frequency is modified by social stimuli. When two males are Introduced both i n i t i a l l y mark at a high frequency but once dominance of one male has been established, the defeated male w i l l cease to mark while the dominant male w i l l continue to do so at a high frequency, actually showing a preference for his opponent's territory* A defeated male w i l l even show an avoidance of his opponent*s odor in a T-tube preference test (Nyby, Thiessen, and Wallace, 1970)* These authors also found that repression of marking i n subordinates was not necessarily 9 related to decreases i n adrogea t i t r e * Thiossen, Owen, and Lindzey (1971) offer the interpretation that given optimal surroundings and no social competition hormonal influences predominate hut that there i s neural control over marking irrespective of hormone levels. Because such measures as frequency of t e r r i t o r i a l marking, gland size, and defecation have been shown to di f f e r for male and female gerbils (Thiessen, Blum, and Lindzey, 1 9 6 9 ) , i t is important to study the effects of the fostering treatment on both sexes. Early experience investigators have typically included only male subjects in their, experiments, thereby ignoring any possible interactions the treatment may have with the sex variable' To summarize, the major purposes of the present study were to assess the effects of the fostering treatment on a variety of adult bel&aviors of the Mongolian ge r b i l , to compare the obtained results with the results of previous studies using mice, for those measures i n common, and to study any differential effects of the fostering treatment on males and females. MSTBXS) Subjects. Toe subjects were Mongol ism gerbils born end raised i n the Department of Psychology's animal colony at the University of B r i t i s h Columbia* The parents were obtained from Tumblebrook farm, Brant Lake, New York and bred at approximately 100 days* The rat mothers were derived from the Long-Evans strain and had been born and raised i n the animal colony* At weaning there were 30 rat-reared (BB) pups and 31 control (0) pups* When behavioral testing commenced, the number of subjects in each condition was as follows: BB male (n= 9), EH female (n =11), C male (n= 16), 0 female (n = 11). One control female died before testing had been completed, reduc-ing the number of subjects i n -&at group to 10 for a l l tests except the open-field* Apparatus* For open-field testing the apparatus was a white board, 2 1*22 m , marked off by black lines into 16 eqial squares and having *3 m high white Masonite walls* A fine mash screen covered the f i e l d during testing. A single lamp suspended above the f i e l d provided the only source of illumination which was set at 1*0 ft-e* The apparatus used for t e r r i t o r i a l marking and fighting tests was a 2 white open f i e l d , 60 cm with walls 19 cm high and covered by a heavy mesh screen* The f i e l d was divided into 16 imaginary (io* unmarked) squares and at the nine intersections removable plexiglass pegs were placed, a l l orien-ted in the same direction* The pegs were 2*6 cm i n length, 1*2 cm In width, and 0*7 cm in height* The surface of each peg was roughened on the top by criss-crossed gouges* Illumination on the floor of the apparatus with the screen i n place was 2*0 ft-o and was provided by a single lamp source* Procedure. Pre weaning treatment: A l l gerbil l i t t e r s were l e f t un-touched with their natural mothers f o r 72 hrs. Each l i t t e r was then r e -moved and placed i n a box with paper shavings for 90 mins to alios any odour to dissipate* Meanwhile, a female lactating rat which bad given birth 48 - 120 ars previously was removed from her own l i t t e r and placed l a a cage with oleen wood shavings. Half of the gerbil l i t t e r was then intro-duced to the rat and the other half returned to the original gerbil mother* Thirteen l i t t e r s were treated i n this manner- Table 1 shows the number of subjects i n eaoh l i t t e r , tiieir assignment to conditions, and the number of subjects surviving in each condition* Of the rat-reared subjects some were raised i n plastic cages, 20*5 cm z 33*0 em z 17*0 cm with wood shavings and some were reared in metal cages 24*0 em z 40*4 em z 17*0 em with plywood floors and wood shavings and paper as nest material. A l l control animals were raised in metal cages under identical conditions to the l a t t e r r a t -reared group* I t was originally Intended that a l l subjects, both experi-mental and control, be reared in plastic cages. However, because the gerbil mothers f a i l e d to care for their young under these conditions they were moved to the metal cages. Gerbils whioh were reared by a rat mother i n plastic cages were allowed to remain there u n t i l weaning. However, for further l i t t e r s born, the cage condition was made constant across groups. Of the rat-reared subjects which survived to be tested, 12 were reared i n plastic cages and 8 i n metal cages* Cages were cleaned four times between fostering and weaning at 23 days • Purina Lab Chess and water were available ad libitum to mother and pups* Post weaning maintenance: from weening to 40 days the subjects were housed i n metal cages similar to those used during the preweaning period i n groups of 2 - 3 littermates per cage without regard to sez* At 40 days the subjects were regrouped according to sez, keeping littermates together where possible. When there was a single subject l e f t over from one l i t t e r , i t was regrouped with animals from another l i t t e r close i n age* This procedure TABLE 1 The Number of Subjects Born. Assignment to Conditions, and Survival Rate within each L i t t e r Bat Mother Gerbil Mother L i t t e r no-Total no* No. of of pups pups at b i r t h fostered No. at weaning No* at testing Males Jfemales No* Of pups festered No* at weaning No> at testing Males iema: 1 9 5 0 0 0 0 4 4 1 1 0 2 5 3 0 0 0 0 2 2 2 2 0 3 9 3 1 1 0 1 3 3 3 2 1 4 9 5 4 2 2 0 4 4 3 2 1 5 8 3 2 2 1 1 5 3 3 1 2 6 7 4 0 0 0 0 3 3 3 1 2 7 6 3 0 0 0 0 3 3 3 2 1 8 5 3 2 1 1 0 2 0 0 0 0 9 8 4 4 3 1 2 4 3 3 3 0 10 9 6 5 3 0 3 3 2 2 0 2 11 6 * 6 6 2 1 1 0 0 0 0 0 12 7 • 4 3 3 1 2 3 2 2 1 1 13 6 *4 ' 3 3 2 1 2 2 2 1 1 Totals *Means 94 7.23 53 4-07 30 3.33 20 9 11 38 3-17 31 2.82 27 mm 16 11 •Reared in metai cages '•Based only on l i t t e r s with at least 1 subject 1? involved only 5 animals: a male and female from Group BR and one male and two females from Group C In no case were experimental and control l i t t e r s mixed* Tba subjects were given ad l i b access to food (Purina Lab Chow and mixed grain) and water* In addition, subjects which developed a cough were administered Megacillin i n wet ground chow u n t i l the infection appeared to subside. Cages were cleaned twice weekly at which time paper was put into the cages* One day before behavioral testing was begun, the subjects were separated and housed in individual cages, where they regained throughout the testing period* The subjects were weighed at 23 days, 60 days, and 100 days of age* Because the subjects varied i n age by as much as 70 days, they were tested i n four separate blocks, each block containing subjects which did not di f f e r i n age by more than 10 days. The schedule for behavioral testing was based on the average age of the subjects within each age block* A l l ages given i n subsequent sections of this paper w i l l therefore refer to the average age of the subjects within a block. Open-field test: Open-field testing began when the subjects were 128 days old* It consisted of 8 daily 5 rain, sessions conducted between 7:00 and 11:00 pm during the dark phase cf the light cycle* Each subject was carried individually i n a transporting cage from the animal colony to the testing room* It was tested then Immediately returned to i t s noma cage* Testing consisted of placing the anixtal i n a designated square of the apparatus and observing and recording certain aspects of i t s behavior for a 5 min period* After each t r i a l the f i e l d was washed with, a mild vinegar solution and dried* The order of testing was systematically varied among the four groups over days, although the order within each group remainsd constant* The following measures were obtained: (a) total number of squares en-tered, with entrance defined as placing at least both forepaws i n a square, 14 (b) "thigmotactic r a t i o " - the number of central squares entered/total number of squares entered, (c) number of seconds spent In the four central squares, (d) number of rears, and le) number of faecal pellets deposited• Paper -shredding test: From day 135 - 137, the paper-shredding a c t i v i t y of the animals was assessed* The test was conducted from 1:30 - 4:30 pm during the l i g h t phase of the cycle* Each subject was removed from i t s home cage and placed i n a temporary holding cage for 20 mlns during which time the home cage was cleaned and a l l bedding material and food removed* Four folded sheets of paper, 28*8 cms 15*1 cm, which together weighed 33*0 g -0*2 g were placed on the floor of the cage* Each subject was then returned to i t s respective home cage and l e f t undisturbed for 2*5 hrs* To avoid the po s s i b i l i t y of soiling the paper and thereby adding extraneous weight, food and water were not available during this time* At the end of the testing period, the gerbils were again removed from their home cages and placed i n the holding cages. The plywood floors were turned over and the paper dumped into the mesh bottom of the home cage* Shredded paper was f i l t e r e d through the metal grids and remaining paper weighed* Subjects were then returned to their hems cages with the plywood floors replaced, and bedding material, food, and water available ad l i b * The identical procedure was followed on the two following days* T e r r i t o r i a l marking test: From day 138 - 145, subjects were tested nightly between 7:00 - 11:00 pm for t e r r i t o r i a l marking' Each subject was treated In the same manner as for open-field testing* During a 5 min obser-vation period the experimenter recorded the frequency of ventral marking responses with a hand t a l l y * Noise from the Insiarument was muffled by wrapping a towel around the experimenter's hand* Only discreet responses directed over the pegs were scored* The number of faecal b o l i were also counted at the end of each t r i a l * The pegs were then removed, soaked i n 15 a mild vinegar solution for 5 mins and dried- The apparatus was also cleaned end dried between the testing of each, subject. The order of test-ing was rotated between each of the four sez-treatment groups each day-Fighting test; Fighting encounters between pairs of subjects were conducted on day 146- Within each sex-treatment group within each age block, subjects were randomly assigned to pairs. Far groups with an odd number of subjects, one animal was randomly chosen to serve twice* Two subjects i n each of the control groups and one subject In each of the r a t -reared groups were used i n two encounters. To Identify each member of a pair their t a i l s were marked with a f e l t pen, one at the base, one at the t i p . Testing was conducted i n the same apparatus as that used to assess t e r -r i t o r i a l marking* Illumination was 2.0 f t - c - The two members of a pair were carried to the testing room in separate cages and placed simultaneously i n the apparatus. A stopwatch was used t o record the latency to fight from the time the pair was introduced* The subjects were separated after 5 sees of fighting and the t r i a l terminated* If a fight did not exceed 3 sees the subjects were not Interrupted and the t r i a l was continued* A maximum latency of 300 seos was allowed* I f a fight did not occur within this time the t r i a l was terminated and scored as negative* In axch an instance a latency of 300 sees was assigned* A t r i a l was scored as positive i f a fight occurred within 5 mins* Only one t r i a l per pair was given* Gland measurement: At approximately 155 days the gerbils were s a c r i -ficed and their ventral sebaceous glands measured* This was dene by c l i p -ping the hair surrounding the gland, measuring i t s length and width with a ruler, and computing the area* HSSULTS An unweighted means analysis of variance procedure (Winer, 1962) was used i n a l l cases where c e l l frequencies were unequal and there was more than one batween-subjects variable* Such, cases included the main analyses on a l l dependent measures with, the exception of weight at 23 days* A l -though n's were unequal for this measure, only one variable (treatment) was involved since the weights for males and females bad been combined within each treatment group* Thus, i t was possible to apply a standard one-way analysis of variance to this measure. Because Group BR included subjects which had been reared in two types of maternity cages, i t was necessary to perform a subsidiary analysis on Group RR scores for each measure i n order to assess the effect of the cage variable* The scores for males and females within each cage con-dition were combined i n these analyses since further partitioning of groups would have reduced the n's to below an acceptable level* Sex was included as a variable in the subsidiary analyses of only tbe 60-day and 100-day weight measures, for which, the n's were somewhat larger* Where repeated measures were obtained on subjects, these scores were added to-gether and the analyses based on the total scores. It was not necessary to use an unweighted means solution for the subsidiary analyses where only one variable was involved. Offspring Mortality. Of the pups fostered to rat mothers, 58*8 per cent survived to weaning at 23 days whereas the survival rate for pups which were l e f t with, their natural mothers was 81*6 per cent* The survival rate of rat-reared pups from the time of fostering to testing at 128 days was only 37*8 per cent* In contrast, 71*1 per cent of the pups raised by gerbil mothers survived to be tested* With, reference to Group BR only, tote pre-meaning survival rate of pups reared in plastic cages was 46'2 per cent compared to 85*7 per cent for pups reared in metal cages* The percentage of rat-reared animals surviving to 128 days was 30*8 per cent for subjects with plastic cage experience and 57*1 per cent for those with metal cage experience* The cause of preweaning deaths was not determined, however k i l l i n g by the mother did not appear to be a major cause since pups found dead were rarely mutilated* In only one case was a r a t mother observed to k i l l a pup and i n no case were gerbil mothers observed to do so* The high mortality rate of rat-reared pups between weaning and t e s t -ing was primarily due to an epidemic of a streptococcus lung infection* The cause of death was determined i n only one animal but the symptoms were similar i n others* The four deaths whieh occurred i n the control group between, weaning and testing a l l involved animals which developed a skin infection and were eliminated by the experimenter* A f i f t h animal died before testing was completed, presumably from a respiratory ailment* Refer to Table 1 for a summary of survival rates of individual l i t t e r s * Body Weight* The means for body weight at 23, 60, and 100 days of age are summarized in Tables 2 to 4* At 23 days, gerbils reared by rat mothers weighed more than gerbils reared by gerbil mothers (F=9 -81; df=1/59; p_ < *0l) • Analysis of cage type within Group BR indicated that gerbils reared i n metal cages were heavier at weaning than gerbils reared in plastic cages (P=62*46j df=1/28; £<*01)* At 60 days, however, control gerbils weighed significantly more than their rat-reared counterparts (£=31*56; of =1/52; p<*01)* A weight d i f f e r -ence between males and females was also apparent at this age (F=15*01; TABLE 2 18 Means of 23 Day Weight (grams) Control Bat-reared 19.13 22-28 Plastic Metal 19.31 26-73 TAFTW 3 Means of 60 Day Weight (grams) Control Rat-reared Male female Male Female 66-62 53-41 49-87 47-37 Plastic itetal Male Female Male Female 50.13 44-00 49-35 52-78 TABLE 4 Means of 100 Day Weight (grams) Control Hat-reared Male Female Male Female 79.96 62-86 72.41 64-55 Plastic Metal Male Female 68-72 63-22 Male Female 77-02 66-87 19 df=l/53; p_<*0l), and i n addition, the interaction between treatment and sex was significant (F=6*97; df=l/52; p_<*05)* The weight difference between control males and females was greater than that between rat-reared males and females* The subsidiary analysis for this measure did not reveal any significant effects due to cage type, sex or cage x sex* For weight at 100 days, the fostering treatment f a i l e d to differentiate between the subjects* On the other hand, sex was a highly significant source of variance at this age (F=26*87; df =1/44; p_<.01)* The treatment x sex interaction was no longer s t a t i s t i c a l l y r e l i a b l e , as i t was at 60 days, but the male - female weight difference was s t i l l less pronounced i n Group EH than i n Group 0 (F=3*69; df=l/44; £ < * 1 0 ) * Sex was the only s i g -nificant source of variance i n the subsidiary analysis (Fj=5*09; df=l/16; £<*05) * The analyses for the three weight measures are summarized in Tables 5 to 10* Open-field Test. Fig* 1 shows the mean number of squares entered on each of the successive test days for males and females of each treatment group* Gerbil-reared gerbils looomoted significantly more than rat-reared gerbils (F=9*21; df =1/43; p_<-0l)* There was no difference between the activity level of males and females and the interaction was also nonsignif-icant* There was a general decline i n locomotion over the eight tests for a l l groups (F=34*97; df=7/501; £<*01) and a significant treatment x sex x days interaction (F=2*70; df =7/301; j><*05). This interaction apparently reflects the different ordering of the four groups on different days* The other interaction terms f a i l e d to attain significance* As Fig* 2 shows and analysis confirmed, there was no difference i n a c t i v i t y between rat-reared subjects with plastio and metal cage experience* The data analysis i s summarized in Tables 11 and 12* TABLE 5 20 Summary of Analysis of Variance of 23 Day Height: Treatment Source of Total 60 Treatment 1 Error 59 TABLE 6 Summary of Analysis of Variance of 23 Day Weight: Cage Type within Group BR Source Total Cage Error s s JUS r p 1057-16 150-75 150.75 9.81 <-01 906-41 15.36 df SS MS S p 29 573.73 — 1 396.05 396.05 62.46 <-01 28 177-68 6-34 21 TABLE 7 Summary of Analysis of variance of 60 Day Weight: 'ixeatment Source df SS MS Jf P Treatment 1 1794.38 1794.38 31-56 <«01 Sex 1 852.69 852.69 15-01 <«01 T x Sex 1 396.08 396-08 6 . 9 7 <.05 Error 52 2953.26 56-79 TABLE 8 Summary of Analysis of Variance of 60 Day Weight: Cage Type within Group SR Source df SS MS J? P Sex 1 10-39 10-39 < 1 n«s. Cage 1 91-36 91-36 1.60 n-s. C x S 1 130-41 130-41 2.29 n-s-Error 21 1194.71 56-89 . . . — 22 TABLE 9 Summary of Analysis of Variance of 100 Day Weight: Treatment Source df SS MS F P Treatment 1 98.67 98-67 1-48 n.s. Sex 1 1791.01 1791-01 26*87 <.01 T x S 1 245.41 245-41 3.69 n.s. Error 44 2932-87 66-65 —— TABLE 10 Summary of Analysis of Variance of 100 Day Weight: Cage Type within Group RR Source df SS MS F P Cage 1 169-93 169.93 3.30 n.s-Sex 1 261-45 261-45 5-09 <-05 C x S 1 25-65 25-65 < 1 n-s* Error 16 821-80 51*36 250 £ 200[ LU H 5 0 01 1 1 2 4 DAYS Figure 1. 8 Mean number of squares entered during 5-min open-field tests by control males, control females, rat-reared males, and rat-reared females Figure 2. Mean number of squares entered during 5-min open-field tests by rat-reared gerbils raised in metal and plastic cages TAHLai 11 25 Summary of Analysis of Variance of Total Squares: Treatment Source df SS MS JF P Treatment 1 60746*785 60746.785 9-21 <.01 Sez 1 SO-578 30.578 <1 n«s« T z S 1 473.639 473.638 <1 n*s> Error Between 43 283779.310 6599.519 — Bays 7 231901.160 33129.737 34.97 <.01 T z D 7 8069.086 1152.726 1.22 n.s* S z D 7 2885-996 412-285 <1 n.s. T x S z B 7 17884.418 2554.917 2.70 <-05 Error Within 301 285129.520 947.274 — — TABLE 12 Summary of Analysis of Variance of Total Squares: Cage Type within Group BR Source df SS MS JP p Total 19 1078653 Cage 1 65965 65965 1-17 Error 18 1012688 56260 — t 26 The ma an rearing scores over days are presented i n Fig* 3* i t can be seen that both male and female control gerbils reared more than their rat-reared counterparts (F=8*86; df=1/43; p_ <*C1) • There was no d i f f e r -ence i n frequency of rearing between the two sexes and the treatment x sex interaction also f a i l e d to reach significance* A significant days effect i n rearing primarily r e f l e c t s the increase from Day 1 to Day 2, which a l l four groups exhibited (F=3*13; df=7/301; £ < * & } • For the remainder of tests rate of rearing showed no consistent trend* None of the interactions with the days varlabia was significant. As Fig* 4 indicates, there was no evidence that cage type experience influenced rearing frequency within Group BB* Analyses of rearing scores are summarized in Tables 13 and 14* Fig* 5 indicates that time spent i n the center squares was unaffected by either the sex of the subjects or the type of mother they had* Analysis of the results yielded a nonsignificant sex effect, a nonsignificant treat-ment effect, and a nonsignificant interaction between the two variables* A significant days effect r e f l e c t s the tendency for center time to increase over days, reaching an asymptote at about Day 3 (Fj=4*73; df=1/301; £<*01)-The only significant Interaction was that of treatment with days (F=2*14; df=7/501; p<*05). Both treatment groups show a parallel increase in center time u n t i l Day 5 when Group BB exhibits a sharp decrease* On the other hand, Group C does not show a deolina i n center time u n t i l Day 8* Analysis of the cage variable within Group BB revealed a marginal but non-significant effect (F=4*06; dffl/18; j><.10). As F i g . 6 suggests, gerbils reared In metal cages showed a slight tendency to spend mare time i n the center than those reared i n pla s t i c cages* The analyses of center time data are summarized i n Tables 15 and 16* The thigmotactlc r a t i o i s a measure of the degree of wall-hugging Figure 3. Mean number of rears during 5-min open-field tests by control males, control females, rat-reared males, and rat-reared females Figure 4. Mean number of rears during 5-min open-field tests by rat-reared gerbils raised in plastic and metal cages TABLE 13 29 Summary of Analysis of variance of Bears: Treatment Source af SS MS X P Treatment 1 5880.012 5880.012 8.86 <.01 Sex 1 1-308 1*308 <1 n.s. T x S 1 68.344 88.344 <1 n«s. Error Between 43 28553.570 664.036 — Says 7 1637-930 233.990 3-13 <.01 T x B 7 723.809 103-401 1.38 n.s. S x D 7 376.311 53-759 < 1 n*s. T x S x B 7 256-175 36*596 <1 n*s* Error Within 301 22534.600 74.864 — -TABLE 14 Summary of Analysis of Variance o f Rears: Cage Effect within Group RR Source af SS MS js' p Total 19 49664.0 — — Cage 1 3255.2 3255.2 1-26 n.s* Error 18 46408.8 2578-3 Figure 5. Mean number of seconds spent in the central area of the open-field on each 5-min test by control males, control females, rat-reared males, and rat-reared females Figure 6. Mean number of seconds spent in the central area of the open-field on each 5-min test by rat-reared gerbils raised in matal and plastic cages T A B U 15 32 Summary of Analysis of Variance of Center Time: Treatment Source df SS MS t P Treatment 1 70304.076 70304-076 1-05 n.s. Sex 1 108.342 108-342 <1 n«s. T x S 1 1.699 1.699 <1 n.s* Error Between 43 2871452.670 66777.969 — Days 7 443341-539 63334.506 4.73 < .01 T x D 7 200451.521 28635-932 2.14 < .05 S i a 7 56963-516 8137.645 <1 n«s. T l S i D 7 110975-806 15853*687 1 1 8 n-B« Error Within 301 4027736.700 13381.185 • — « . TABLE 16 Summary of Analysis of Variance of Center Time: Cage Type within Group KB Source df SS MS F p Total 19 89220.82 — — Cage 1 16426-80 16426-80 4*06 n.s. (<10) Error 18 72794-02 4044-11 3 3 exhibited by an animal• Since the open-field contains 16 squares, 4 central and 12 peripheral, one would expect to obtain a thigmotactic ratio of .25 i f the animal was entering the squares randomly* Thus a r a t i o of less than •25 indicates an avoidance of the center squares (or an attraction to the peripheral ones) while a ratio of greater than .25 indicates the reverse* As Fig* 7 i l l u s t r a t e s , there was l i t t l e difference between the thigmo-tactic ratios of males and females or between those of rat-reared and con-t r o l gerbils* Analysis of these data (summarized i n Table 17) showed that sex, treatment, and the interaction between them were a l l nonsignificant sources of variance. Analysis further revealed a significant days effect (F=10*92; df=7/301; £<*01)* and a barely significant interaction of treat-ment with days (F=2*20; df=7/501; £ < * 0 5 ) . The remaining interactions were not significant. It can be seen from F i g . 7 that the thigmotactic r a t i o f i r s t increases, then decreases over days* I n i t i a l l y the rat-reared gerbils have a higher mean r a t i o than the control gerbils but the r a t i o s of the two groups be coma more similar on later tests* The subsidiary analysis (summar-ized i n Table 18) showed cage type to be a highly significant source of variance (F=21*36; df=l/l8; p_<.01). Subjects of Group RR that were reared in metal cages tended to have higher thigmotactic ratios than those reared in plastic cages. This relationship i s shown in F i g . 8. Fig. 9 presents the mean number of faecal b o l i deposited in the open-f i e l d by each of the four groups over the eight test days. As seen in Fig. 9, males defecated more than females. Analysis of variance gave a s i g -nificant effect due to sex (F=24.77; df=l/43; £<*01), a nonsignificant treatment effect, and a significant days effect (F=5.09; df =7/501; p_<.01). The only interaction to attain significance was sex x days (F=3*25; df=3*25; £<* 0 1 ) . While the frequency of defecation increased over days for a l l Figure 7. Mean thigmotactic ratio of control males, control females, rat-reared males, and rat-reared females during 5-min open-field tests Figure 8. Mean thigmotactic ratio of rat-reared gerbils raised in metal and plastic cages during 5-min open-field tests TABLE 17 Summary of Analysis of Variance of Thigmotactic Ratio: Treatment Source df SS MS F P Treatment 1 121.05 121-05 1-32 n*s. Sex 1 250*72 250.72 2.73 n.s* 1 x 8 1 25.64 25.64 < 1 n.s. Error Between 43 3953.29 91.94 — Days 7 1849-04 264.15 10.92 <.01 T x D 7 372-81 53.26 2.20 <-05 S x D 7 54*53 7-79 <1 n.s> T x S x D 7 216.88 30.98 1-28 n.s« Error Within 301 7277-49 24.18 — TABLE 18 Summary of Analysis of Variance of Thigmotactic Ratio: Cage Type within Group RR Source df SS MS F p Total 19 .5791 — Cage 1 -3141 .3141 21-36 <.01 Error 18 . 2650 «0147 — — 37 groups, males showed a much sharper i n i t i a l increase than females did. Within Group EH, cage type experience also influenced defecation i n the open-field (F=7«52; df=l/l8; p_<.01). Those subjects which had the metal cage pre weaning environment defecated more than those with p l a s t i c cage experience. Fig. 10 ill u s t r a t e s this effect. The analyses of variance for open-field defecation are summarized i n Tables 19 and 20. Paper-shredding Test. Fig. 11 shows the amount of paper shredded on three consecutive test days for the four groups of subjects* No significant main effects or interactions were found when analysis of variance was ap-pl i e d to the data. Although males tended to shred more paper than females, this difference did not reach the criterion for significance (F=3*89; d£=l/42; £ < * 1 0 ) . The subsidiary analysis, on the other hand, produced a highly significant difference between the metal cage and plastic cage subjects (F=25-80; df=lA8; £ 0 0 1 ) . Those subjects with early experience in the metal cages shredded more paper on the three tests than those sub-jects with early p l a s t i c cage experience* This difference i n paper-shredding activity can be seen i n Fig. 12* The analysis of variance summaries are presented i n Tables 21 and 22* T e r r i t o r i a l Marking Test. Fig* 13 indicates an effect on frequency of t e r r i t o r i a l marking due to sex as well as an interaction between sex and treatment* Analysis of variance gave a nonsignificant treatment effect and a significant sex effect (F= 12*08; df=l/42; £<*01), but showed the inter-action between sex and treatment, which i s Indicated i n Fig* 13, to be only marginal (F=3*01; df=l/42; £<*10)* In addition, analysis revealed a s i g -nificant days effect (F=11.76; df=7/294; p<*Ol), a nonsignificant treatment x days effect, a significant sex x days effect (F=2*06; df=7/294; j><*05), and a significant t r i p l e interaction (F=£*97; df=7/294; £ < * 0 1 ) . Figure 9. Mean number of boli deposited on each 5-min open-field test by control males, control females, rat-reared males, and rat-reared females 40 TABLE 19 Summary of Analysis of variance of Open-field B o l l : Treatment Source df SS MS F P Treatment 1 115.072 115-072 2.25 n.s* Sex 1 1268-108 1268.108 24-77 <.01 T x S 1 97-302 97-302 1.90 n.s. Error Between 43 2201-305 51.193 — Days 7 311-196 44-457 • 5.09 <-01 T x D 7 28-034 4-005 <1 n.s. S x D 7 198.556 28.365 3*25 <.01 T x S x D 7 41-201 5.886 <1 n-s-Error Within 301 2628-834 8.734 — — ——•* TABLE 20 Summary of Analysis of Variance of Open-field Bo l l : Cage Effect within Group BR Source df S3 MS F P Total 19 8924.95 — Oage 1 2632.03 2632.03 7.52 < .05 Error 18 6292.92 349.60 — ..... 1 5 i — Z LU < a. Z 2 0 1 I 2 D A Y S Figure 11* Mean number of grams of paper shredded during 2.5 hr tests by control males, control females, rat-reared males, and rat-reared females Figure 12. Mean number of grams of paper shredded during 205 hr tests by gerbils raised in metal and plastic cages TABLE 21 Summary of Analysis of Variance of Paper Shredded: Treatment Source df SS US P Treatment 1 30.16 30.16 <1 n-s-Sex 1 15652.64 15652.64 3.69 n*8*(<10) T x S 1 132.44 132.44 n.s* Error Between 42 169100.00 4026.19 — — — Bays 2 294.16 147.08 <1 n«s. I z D 2 1244-54 622.27 <1 n.s> S x D 2 507-26 253.63 <1 n>s. T i S x D 2 461.15 230.58 <1 n.s. Error Within 84 57676-96 686.63 — _ TABLE 22 Summary of Analysis of Variance of Paper Shredded: Cage Type within Group RR Source df SS MS F p Total 19 2587.43 — Cage 1 1523.68 1523-68 25*80 <-01 Error 18 • 1063*75 59.03 — — — — It i s apparent from Fig. 13 that frequency of t e r r i t o r i a l marking ex-hibits a steady increment from Day 1 to Day 8 and this increment is steeper for males than females. Of the four groups, HR males show the most rapid increase in marking scores while RR females display v i r t u a l l y no increment at a l l * For C males and females marking frequency rises at about the same rate. It i s these di f f e r e n t i a l rates of acceleration among the four groups that account for the significant t r i p l e interaction. Fig. 14 gives no evidence that early cage type experience influenced frequency of t e r r i t o r i a l marking. Analysis confirmed this lack of relationship. Analysis of variance summaries for t e r r i t o r i a l marking are presented i n Tables 23 and 24. The measure of defecation which was taken during t e r r i t o r i a l marking tests, i n general parallels the open-field defecation scores* The relationship between sex, treatment, and defecation i n the marking apparatus i s ill u s t r a t e d i n F i g . 15. Males defecated more than females (F=17.09; df=l/42; p_<-01) and rat-reared subjects defecated less than controls but the latter difference did not attain significance (F=3.90; df=l/42j p_<.10). A l l other main e f -fects and interactions were nonsignificant. For this measure, defecation scores were at about the same lev e l on Day 1 as they were on Day 8 of open-f i e l d testing. That t h i s level i s asymptotic i s Indicated by the lack of a significant days effect on the second b o l i measure. Analysis i s summarized in Table 25. The effect of cage type experience on defecation which was obtained for the open-field test i s less apparent for the marking test, as F i g . 16 shows. Analysis of variance (summarized i n Table 26) f a i l e d to yield a significant effect for cage type experience. Gland Size. Table 27 shows the mean ventral gland size of each of the groups. Analysis of gland size (presented In Table 28) revealed a nonsignif-icant treatment effect, a significant sex effect (Fj=96.20; df=l/42; £ < ' 0 1 ) , Figure 13. Mean number of ventral marking responses performed in apparatus on each 5-min test by control males, control females, rat-reared males, and rat-reared females Figure 1 4 . Mean number of ventral marking responses performed in apparatus on each 5-min test by rat-reared gerbils raised in metal and plastic cages TABLE 23 k6 Sunmary of Analysis of Variance of Te r r i t o r i a l Marking: Treatment Source df SS MS F P Treatment 1 707.177 707-177 1.11 n-s-Sex 1 7691.239 7691-239 12.08 <-01 T x S 1 1915.502 1915.502 3.GEL n-s-(<f10) Error Between 42 26737-750 639.613 — Days 7 1802-732 257-533 • 11-76 <-01 T x D 7 118-245 16.892 <1 n-s. S x D 7 316-286 45.184 2.06 <.05 T x S x D 7 456-060 65.151 2-97 <-01 Error Within 294 6441-028 21.908 _ . . . TABLE 24 Summary of Analysis of Variance of Territorial Marking: Cage Type within Group BR Source df SS MS F p Total 19 124785 Cage 1 6923 6923 1*06 n-s-Error 18 117862 6547 — — A _ A RRF I 1 1 I I I - I - J 1 2 3 4 5 6 7 8 D A Y S _ •»>• Figure 15. Mean number of boli deposited during 5-min tests in marking"apparatus by control ^ males, control females,rat-reared males, and rat-reared females PLASTIC •o METAL 8 O 09 y. o d z < m 0 1 D A Y S 8 Figure 16. Mean number of boli deposited during 5-min tests in the marking apparatus by rat-reared gerbils raised in metal and plastic cages TABLE: 25 ^9 Summary of Analysis of Variance of Defecation i n the Marking Apparatus: Treatment Source df SS MS r P Treatment 1 221-238 221.238 3.90 n.s -K-10) Sez 1 968.905 968.905 17.09 <.01 T z S 1 30-417 30-417 <1 n-s-Error Between 42 2381-720 56-708 Days 7 68*022 9.717 1-43 n-s-T z D 7 33-215 4.745 <1 n.s* S z L 7 53.120 7-589 1-12 n-s. T x S z D 7 60.692 8-670 1-28 n.s. Error Within 294 1992.551 6-777 TABLE 26 Summary of Analysis of Variance of Defecation i n the Marking Apparatus: Cage Type within Group fiH Source df SS MS JF p Total 19 9286 — — — Cage 1 701 701 1.46 n.s. Error 18 • 8585 477 — — 50 and a nonsignificant interation- Early cage type experience also had no effect on the gland size of rat-reared gerbils* The subsidiary analysis i s presented i n Table 29* Fighting Test* Table 30 shows the number of pairs of animals i n each of the four groups which fought* A chi-square analysis which was applied to the male fighting frequencies f a i l e d to show a significant difference 2 between Group BB and Group C males (X =1*98; df=l; p_>*05). Because f i g h t -ing frequencies for the two female groups were identical, no s t a t i s t i c a l analysis was performed on these data* The mean fighting latencies for each of the four groups are presented in Table 31* Raw scores for each pair of subjects were transformed to log (x+1) sec* Analysis of variance, summarized i n Table 32, fa i l e d to reveal any significant main effects or interactions* HO subsidiary analysis was carried out on Group BB data because the group n's were too m a l l (7 and 4 respectively for the plastic and metal cage conditions)* Relationships Among Dependent Measures. To obtain a representative score for each animal on the open-field and t e r r i t o r i a l marking measures, the scores for the last four tests' (test days 5 through 8 of eaoh test) were summed. The reason for using only the last four test scores was that behav-ior was presumably more stable later i n testing than on i n i t i a l tests. Thiessen at al.(1969) also used only data from the last four days i n cor-relating various open-field behaviors of gerbils. Representative scores for paper shredding were obtained by summing each subject's scores over tests 1 through 3* Obviously only one measure of gland size for each subject could be used* On the basis of these scores a l l possible product moment corr e l -ation coefficients among the nine measures were computed* A separate coef-ficient was computed for each of the four sex-treatment groups. The inter- , correlation matrix appears in Table 33* TABLE 27 Means of Ventral Gland Size (sojiare centimeters) 51 Control Male 1.48 Female 0.60 Bat-reared Male female 1.68 0-65 Plastic Male Female 1.50 0-86 Metal Male Female 1.90 0.29 TABLE 28 Summary of Analysis of Variance of Ventral Gland Size: Treatment Source df SS MS F P Treatment 1 0-1711 0-1711 1*64 n.s* Sez 1 10-0046 10.0046 96-20 < .01 T z S 1 0.0625 0.0625 <1 n.s* Error 42 4-3717 0.1040 — TABLE 29 Summary of Analysis of Variance of Ventral Gland Size: Cage Type within Group RR Source df Total 19 Cage 1 Error 18 SS MS F p 7.5203 0*0052 0*0052 <1 n.s* 7-5151 0.4175 TABLE 30 Number of Pairs Which Fought Control Bat-reared Male 5/9 (56ft) 5/5 {100%) Female 1/6 (17?o) 1/6 (17ji>) TABLE 31 Means of Fighting Latencies (seconds) Control Bat-reared Male Female Mqlft Female 177*3 £86.5 115-2 293.7 TABLE 32 Summary of Analysis of Variance of Latency to Fight: Treatment Source df SS MS F P Treatment 1 0-0114 0.0114 <1 n-s-Sex 1 0-5471 0-5471 1-40 n-s-T x Sex 1 0-0167 0-0167 <1 n-s-Error 22 8.5906 0-3905 mm mm mm TABLE 33 54 Correlations between Behaviors 0«F- Rears TMg. Center lerr - Mk- Paper Gland B o l i Ratio Time Mark. Boli Size CM •11 •76*** —34 • 28 —32 .41 -.13 —22 Total CF —25 .68* -•51 -.49 — 13 -.12 •48 -27 Sqs. REM •15 • 30 —02 .59 —47 •45 •10 • 33 RRF -12 •47 • 04 • 43 •19 .09 • 21 -•22 Open- CM .10 -.02 —08 -.07 •11 —12 —01 f i e l d CF -34 • 54 .42 — 04 • 32 • 08 •74* Bo l l RRM .00 .65 • 28 .52 .21 .94*** .72* RRF • 38 •47 • 38 -.83 ** .37 • 62* — 58 CM -.22 •14 -.16 .28 —08 — 30 Bears CF — 29 —17 —47 • 20 .44 —53 RRM • 21 • 34 —18 —10 —06 —42 KRF .25 • 57 -.47 -•02 •SO —58 CM •68** —02 —46 —04 -.18 Tnlg. CF •88* * * • 28 •11 -.29 .46 Ratio RRM • 28 •05 —10 .56 • 26 RRF .80** -.63* -01 •47 -.77*' CM -.16 -07 —39 — 21 Center CF •42 —15 -•05 •82 Sloe RRM —19 -•22 .26 •13 RRF -.31 —06 • 69* -.84*' Terr. CM —36 .21 • 64 * Mark- CF —61 • 32 • 00 ing RRM —30 •44 .30 RRF — 32 —37 • 53 Mark- CM. —42 -.31 ing OF —36 • 04 Bo l i RRM •35 .42 RRF •17 • 07 CM —03 Paper CF .29 Shred- RRM .72* ded RRF —81** *p<.05 **p<«01 ***p<.001 DISCUSSION Offspring Mortality. During both the prewesnlng period and the period between weaning and testing, the rat-reared group had a lower i n -cidence of survival than the control group. The cause of preweaning deaths was not determined, however k i l l i n g by the mother did not appear to be a major cause since pups found dead were rarely mutilated. In only one case was a rat mother observed to k i l l a pup and i n no instance were gerbil mothers observed to do so* Some rat mothers t o t a l l y ignored their foster young and i n such cases the entire l i t t e r was lost* Other factors which may have contributed to offspring mortality i n the rat-reared group include the pos s i b i l i t y tiaat pups were inadvertently crushed by the rat mother's weight or that they had d i f f i c u l t y nursing because the nipples were larger and harder to reach. Hudgens, Denenberg and Zarrow (1968) and Paschke et a l . (1971) also report higher mortality rates i n rat-reared mice • The high mortality rate i n Group KK between weaning and testing was primarily due to an epidemic of a streptococcus lung infection* The cause of death was determined i n only one animal but the symptoms were similar i n others. None of the control subjects was a f f l i c t e d . This fact suggests that rat-reared subjects were less resistant to the infection. However, i t i s also possible that the infection originated from a r a t mother and follow-ing weaning spread to animals housed in adjacent cages. Since control sub-jects were housed in a separate cage rack from rat-reared subjects, they may have escaped exposure to the bacteria. The four deaths which occurred in Group C between weaning and testing a l l involved animals which developed a skin infection and were eliminated by the experimenter. A f i f t h animal died before testing was completed, presumably from a respiratory ailmant* Within Group EE there was a lower percentage of preweaning deaths for pups which were reared i n metal cages than fa? pups reared i n p l a s t i c cages* In fact, the survival rate of Group BR pups i n ne ta i cages was comparable to that of control pups, a l l of which were reared i n metal cages* This fact suggests that some aspect of the plastic cage pre-weaning environment was detrimantal to the survival of the pups* The plastic cages differed from the metal cages i n a number of respects, most notably i n volume and level of illumination*' The plastic cages were some-what smaller and had transparent walls* Whether or not the pups were directly affected by these variables is impossible to ascertain, but i t i s quite probable that the mothers' behavior was influenced by cage type* A l -though no attempt was made to record maternal behavior, i t was noted that rat mothers in plastio cages often l e f t their l i t t e r s unattended while rat mothers i n metal cages were observed to leave the nest only occasionally' The fact that some gerbil mothers failed to care for their young i n the plastic cages also indicates that plastic cages cf the type used in the present study do not provide an optimal maternal environnBnt • The differential rate of survival between Group BB and Group C Intro-duces the problem that the results may have been Influenced by a subject selection factor* In other words, Group BR may have included only very hardy individuals whereas Group C may have contained a mare random assort-ment of subjects. There is no way of determining whether or not mortality i n the rat-reared group was random with respect to individual. Furthermore, i f a subject selection factor was operating, there is no way of knowing whether or not i t influenced the results. Unfortunately differential mor-t a l i t y rate has been a characteristic of cross-fostering studies and one should bear this i n mind when interpreting results. Body Weight. Gerbils which were reared by rat mothers weired more at weaning than control gerbils- Increased weaning weight has also been 57 reported for rat-reared mice (Denenberg, Hudgens and Zarrow, 1966; Hudgens et a l - , 1967; Eudgens et a l . , 1968; Paschke et a l . , 1971). How-ever, the weaning weight was found not to d i f f e r from that of control mice when mice were tended by a rat aunt rather than a lac tat ing rat (Denenberg, Rosenberg, Paschke, and Zarrow, 1969). This suggests that where weight differences at weaning are obtained, they may be due to the increased supply of milk provided by the rat mother. A second p o s s i b i l i t y i s that the pups received mere handling from the rat mother than they or-dinarily would from their natural mother and that this increased handling stimulates growth. A study by Bessler (1962) suggests that body weight of pups is positively correlated with maternal handling. Be found that pups of both the B&LB/c strain and the C57BI/10 strain weighed more i f they were reared by BALB/c mothers than i f they were reared by C57BL/10 mothers* In addition BALB/c mothers were shown to handle both strains of pups more than the C57BL/10 mothers did* Although a significant effect of treatment on weaning weight was ob-tained i n the present study, the increased weight for Group BR was limited to subjects reared in metal cages, as Table 2 shows* Therefore, one can conclude that under similar cage conditions rat-reared gerbils weigh more at weaning than control gerbils* The mean weaning weight of Group BR sub-jects which were reared i n plastic cages differed very l i t t l e from that of control subjects. Since pups in plastic cages appeared to suffer greater neglect from the rat than the pups in the metal cages, a reduced body weight along with higher mortality rate i n the former group is not surprising* At 60 days the position of the two treatment groups with respect to body weight was reversed, rat-reared gerbils weighing lass than the controls* This result was to be expected since many rat-reared subjects were suffering from an infection at this time* At 100 days of age there was no weight 58 difference between rat-reared and control gerbils* Open-field Behavior' The assumptions which have core to underlie the use of the open-field are based almost entirely on work with rats* The two most commonly employed open-field measures are defecat ion and locomotory activity* High defecation and low activity have generally been assumed to reflect high emotionality; conversely low defecation and high a c t i v i t y have been associated with low emotionality (Broadhurst. 1958; Goldman, 1969; B a l l , 1934; 1936)* Such a conception of open-field behavior i s probably an oversimplification and has been c r i t i c i z e d by Ader (1969)* In order to account for the open-field behavior of rats over repeated testings, i t is necessary to Introduce at least one additional construct* Montgomery (1955) proposed that exploration or curiosity, as well as fear or emotionality, influenced open-field behavior and Yalle (1971) has expan-ded this notion* In general, exploration and fear are conceived as oppos-ing tendencies* While exploration presumably f a c i l i t a t e s such behaviors as locomotion, rearing, and entering the central souares, fear inhibits these behaviors because i t induces incompatible behaviors such as freezing and withdrawal* Defecation, however, is s t i l l considered a r e l a t i v e l y pure measure of fear, being largely unaffected by exploratory tendencies* The meaning of open-field behavior i n rats is s t i l l a widely debated issue, despite the fact that a vast amount of research has been devoted to the subject' The meaning of open-field behavior i n other species i s even less clear* In mice, Bosenberg, et a l . (1970) suggest that high open-field activity indicates increased rather than decreased emotionality since aotivity was positively correlated with plasma corticosterone level* More-over, Candland and Nagy (1969) report that for mice defecation increases over repeated testings while for rats defecation decreases* These r e l a t i o n -ships are independent of sex* Bruell (1969), however, found that for male mice exploratory behavior and defecation were positively correlated (r = .124) while for female mice a negative correlation existed between the two behaviors, (r= —159). On the basis of these results he proposed that for males defecation serves a largely t e r r i t o r i a l function-Very l i t t l e work has been done on open-field behavior of gerbils (Nauman, 1963; Thiessen, Blum, and Lindzey, 1969). However these studies, as well as the present one, clearly indicate that gerbil open afield be-havior i s very different from that of ra t s and i t would be premature, i f not erroneous, to make similar assumptions regarding i t s meaning. In the present study certain aspects of open-field behavior were af-fected by the nature of the pre-weaning environment. In order to under-stand how the fostering treatment (and cage type experience) exerted their effects, i t is necessary to know sonBthicg about the nature of open-field behavior. Because such information i s largely unavailable, any statement regarding the mechanisms involved i n cross-fostering w i l l , of necessity, be h i ^ i l y speculative. fostering gerbils to r a t mothers resulted i n reduced adult open-field activity as measured by the total.number of squares entered* Therefore the effect of the fostering treatment on the open-field a c t i v i t y of both gerbils and mice is similar* The failure to obtain a sex difference for activity i n the present study is consistent with the results of Thiessen, et al * (1969). .Rodent species in which females engage in mare open-field a c t i v i t y than do males include rats (Masur, 1972; Valle, 1970; Yalle and Bols, 1973), hamsters (Swanson, 1969), and C57BL/6J mice (Nagy and Glaser, 1970)* In mice a sex difference seems to be strain dependent^ as Hagy and Holm (1970) f a i l e d to obtain one for C3H mice• Rearing activity of gerbils i n the open-field was depressed by the 60 fostering treatment, and as was the case with total squares, no sex d i f -ference was found* Hearing data is not available for other rodent species except the rat* Masur (1972), Valle (1970), and Valla and Bols (1973) found that female rats reared more than males. The fact that i n the present study both locomotion and rearing were similarly affected by the fostering treatment and sex suggests that these behaviors may be related* Furthermore, they were shown to be positively correlated although these correlations were considerably higher for the control groups than the rat-reared groups (see Table 33)* It should be noted, however, that t h i s relationship may hold only for the l a t t e r part of testing since scores were based on the last four of the eight days* Indeed locomotion and rearing do not follow similar patterns over days (see Figs 1 and 3)* R'hereas locomotion exhibits an i n i t i a l sharp decline, rearing shows a sharp incline before stabilizing* It Is possible that the meaning of a behavioral measure can change over the course of testing* Denenberg (1969) has postulated that high activity i n r a t s on Day 1 of open-field testing indicates high emotionality whereas high a c t i v i t y on subsequent testing days is indicative of low emotionality* His hypothesis was based on the results of a factor analysis of rat open-field behavior (Whimbey and Denenberg, 1967)* Day 1 ac t i v i t y was found to have a high positive loading on the "emotional reactivity" factor whereas activity on subsequent days had a high negative correlation with emotional reactivity* Since center time and thigmotactic r a t i o both measure the tendency to enter the central squares, i t is not surprising that these measures should yield similar results* For both HB a aires the tendency to explore the cen-t r a l squares appeared to habituate more rapidly in the rat-reared subjects than controls but this effect was barely significant* Whereas wall-hugging was l i t t l e affected by the fostering treatment, i t 61 was sensitive to cage type experience within the rat-reared group, "plastic-reared" subjects tending to exhibit more wall-hugging, than "metal-reared* subjects. Visual and tactile factors may play an import-ant role i n the development of wall-hugging behavior and the two cage types differed in a number of physical properties which have been discussed previously (see page 56). These differences may account for the observed differences in thigmotactic behavior of the "metal-reared" and " p l a s t i c -reared" subjects* Although "metal-reared" subjects i n Group RR were less thigmotactic than "plastic-reared" subjects, they defecated more. In fact, defecation of rat-reared subjects raised i n metal cages was comparable to that of the control subjects. The reduction i n defecation far Group RR males apparent in Jrig. 9 i s therefore largely due to reduced defecation for " p l a s t i c -reared" subjects only* The fact that the sex x treatment interaction f a i l e d to reach significance also indicates that the v a r i a b i l i t y within the rat-reared group was considerable • Thus the present study provides no evidence that the fostering treatment reduces defecation i n gerbils as i t does in mice* The large sex difference for defecation is i n agreement with the r e -sults of Thiessen et a l . (1969) and is also in the same direction as the sex difference obtained far rats (Masur, 1972) and mice (Brusll, 1969). The obtained increase i n defecation scores over days i s not consistent with an interpretation of defecation i n terms of fear, since fear should de-crease with repeated exposures to the situation. Moreover no significant negative correlations were obtained between open-field defecation and those behaviors which fear has been assumed to inhibit (total soxares, rears, thigmotactic ratio, and center time). However, i t may also be erroneous to assume that the lat t e r behaviors are, in fact, inibited by fear-62 The assumption that low ac t i v i t y Indicates high, emotionality i s based on the observation that freezing (presumably an emotional response) inhibits locomotion* Freezing, however, is a rarely observed response of gerbils placed i n an open-field and a l l gerbils exhibit high levels of ac-t i v i t y (relative to rats)* Therefore individual differences i n open-field activity of gerbils probably r e f l e c t variations i n running speed rather than differences i n amount of freezing* The fact that gerbils engage i n far less wall-hugging than do rats may mean that for gerbils this behavior i s not a sensitive index of the level of fear* It may also be a poor measure of exploratory tendencies i n the gerbil since the animals enter the central squares at near chance frequen-cies* Perhaps i t i s for this reason that the wall-hugging measures showed no consistent relationship with total squares or rears, as indicated in 'liable 33* Paper Shredding. Rearing gerbils with r a t mothers appeared to have no effect on the amount of paper they shredded as adults* Despite the fact that rats do not engage in this behavior, rat-reared gerbils shredded paper as vigorously as did the control gerbils* This result indicates that paper shredding requires no learning from the mother* However, further conclu-sions regarding i t s development cannot be drawn u n t i l more is known about this behavior* The present study indicates that males tend to shred more paper than females, although this difference was not significant and requires further investigation. Glickman, Fried, and Morrison (1967) f a i l e d to obtain a sex difference for paper shredding but their saaple included only six animals of each sex* While amount of paper shredding was highly resistant to any influence by the fostering treatment,, i t was clearly affected by early cage type within Group RR, "xnstai -reared" subjects engaging i n more paper-shredding than "plastic-reared" subjects • No explanation can be offered for this result at the present time* Squally puzzling are the significant positive correlations which were obtained for Group RR sales between paper shred-ding and open-field defecation, and paper shredding and gland size- For Group RR females paper shredding correlated positively with open-field defecation but negatively with gland size* No comparable correlations were obtained for control animals (see Table 33)• Whether or not these cor-relations were spurious, perhaps a result of a subject-selection factor within Group RR, i s not possible to ascertain end remains to be determined by future replication-Although i t is not clear uhat paper shredding represents or what fac-tors influence i t s occurrence, i t does not appear to be related to loco-mo tor y a c t i v i t y or rearing since there were no significant positive cor-relations between paper shredding and these behaviors. Te r r i t o r i a l Marking and Gland Size. The effects of fostering on f r e -quency of t e r r i t o r i a l marking were somewhat inconclusive. Fostering ap-peared to elevate marking i n males while depressing i t i n females, yet this interaction of treatment x sex did not quite reach the -05 level of s i g n i f -icance. Fostering did, however, have a differential effect on the rate of ac-celeration of the marking response over days for sales and females (indic-ated by a significant interaction of treatment x sex x days). An increase in marking frequency with repeated exposure to the test situation has been reported fee both male and faaale gerbils (Thiessen et a l . , 1969) and was also found i n the present study. Low marJcing scores on Day 1 of testing may be due to the predominance of exploratory responses . which, interfere with t e r r i t o r i a l responses- The habituation of exploratory 64 responses with repeated testing may then permit the expression of t e r r i t o r -i a l tendencies. Fear may also inhibit mar King on i n i t i a l tests, Thus r a t -reared males may adapt to the test situation at a more rapid rate than con-t r o l males but why the fostering treatment should not have the same effect on females i s unclear. The measure of defecation which was recorded in the Barking apparatus was primarily for cdnparison with the open-field defecation measure. The correlations between these two defecation measures were surprisingly small (see Table 33) t indicating that either (a) defecation i s not a very reliable measure or lb) subjects responded differently to the two apparatuses. A l -though both p o s s i b i l i t i e s may be true, support for the former comes from the results of Thiessen et a l . (1969). They reported f a i r l y low r e l i a b i l i t y co-efficients for defecation in a marking apparatus 1.34 and .24 for males and females respectively). Evidence that defecation i n gerbils serves a t e r r i t o r i a l function was somewhat contradictory. Correlations between marking and both defecation measures were negative in seven out of eight cases although i n only one i n -stance was the coefficient r e l i a b l e . Marking and open-field defecation cor-related -.83 in Group BR females- Despite the lack of positive association between marking and defecation, there was an increase in defecation f r e -quency with repeated exposure to the open-field- The l a t t e r result i s con-sistent with a t e r r i t o r i a l interpretation of defecation- Clearly, further investigation is necessary to establish the function of defecation i n gerbils-The large sex difference obtained for marking frequency as well as gland size confirms earlier findings. Furthermore marking and gland size cor-related positively (.64) for control males- The lack of relationship for other groups probably r e f l e c t s the fact that marking i s influenced, by fac-tors other than androgen t i t r e , especially i n females I Thiessen, Owen, and Lindzey, 1971)-The fact that the fostering treatment had no influence on the sebac-eous gland size of gerbils indicates that levels of circulating androgens were similar i n rat-reared and control subjects, (assuming that gland size i s a reliable index of androgen t i t r e ) • 'ifherefore, any differences i n marking behavior between rat-reared and control subjects cannot be a t t r i b -uted to differences i n androgen levels* Fighting. The results of the fighting test are inconclusive because of the small number of pairs tested as well as the fact that a few subjects were tested twice while the majority were tested only once. However, i t i s probably safe to conclude that fostering gerbils to rat mothers does not reduce incidence of fighting as is the case for fostered C57BL/10 J mice. One hundred per cent of the rat-reared male pairs fought compared to f i f t y - s i x per cent of control male pairs. Whether or not ra t -reared males actually exhibit a significantly greater incidence of fighting than control males remains to be determined. The observed incidence of fighting for females was identical (seventeen per cent) for both groups-The latency to fight revealed no additional Information- Mean laten-cies were s l i g h t l y shorter for rat-reared males but not significantly so-The failure of this measure to reveal a sex difference undoubtedly reflects the small sample size. 'rales sen et a l . (1971) report that females fight only occasionally, although no s t a t i s t i c a l date, axe given. CONCLUSIONS The only clear-cut effect of fostering gerbils to rat mothers was a reduction i n activity as measured by both open-field locomotion and rearing. However the interpretation of this reduced activity must be largely spec-ulative as very l i t t l e additional data to the present results are available-There are at least three possible explanations for reduced a c t i v i t y as 66 a result of fostering- The f i r s t is that fostering reduces emotionality' This interpretation i s favoured by Denenberg (1970) to account for the effects of fostering mice to rat mothers- That high ac t i v i t y i s assoc-iated with high emotionality i n mice receives support from the finding that activity and corticosterone response to a novel stimulus are posit-ively related (Rosenberg et a l - 1970)* It has been argued earl i e r i n the present paper (p- 62) that for gerbils a c t i v i t y i s not related t o emotionality- Following this argument, i t i s unlikely that the observed reduction in act i v i t y for rat-reared gerbils was a result of either i n -creased or decreased emotionality* A second possible explanation i s that fostering gerbils to rat mothers reduces their curiosity or "exploratory d r i v e T h o m p s o n and Lippman (1972) recently proposed that gerbils are more exploratory animals than rats- Using a Greek cross maze with black, white, striped, and check-ered compartments, these authors found that on early t r i a l s gerbils had a greater tendency to explore a l l compartments whereas rats showed a marked preference for the black one* Thus i f rat mothers cause their gerbil fos-ter pups to become mere r a t - l i k e i n some respects, a reduction i n explor-ation would be i n the predicted direction* It i s also possible, however, that locomotion and rearing measure nothing more than a general activity factor • A c t i v i t y level i s to some extent genetic, and within a range of v a r i a b i l i t y , fixed for a given species* For example, gerbils and rats d i f f e r with respect to activity level and this difference may depend to a large extent on biochemical and metabolic d i f -ferences which have no relation to differences i n emotionality or curiosity between the two species* Although the concept of a general a c t i v i t y factor may not be a particularly useful or meaningful one, i t i s introduced into the present context simply as a label for those variables which influence 67 a c t i v i t y but which, are unrelated to the conceptual variables, emotionality and curiosity* Because i t is not possible to separate a curiosity factor from a general activity factor in the present study, either could have been af-fected by the fostering treatment. However i t may be possible to separate them by comparing a c t i v i t y i n a novel environment such as an open-field, with a familiar environment such as a home cage. If the animals differed i n curiosity but not general a c t i v i t y , then presumably their home cage ac-t i v i t y would be similar. Unfortunately such observations have not been made but they would aid interpretation of the present results considerably. Since early cage type experience appeared to have no effect on loco-motion or rearing frequency of rat-reared gerbils, i t i s very unlikely that cage type could account for the treatment effect on these measures. Early cage type experience did, however, have definite effects on later behavior although these effects were quite different from those of cross-fostering, fiat-reared gerbils which were housed i n plastic cages be-fore weaning, as opposed to metal cages, had a greater tendency to wall-hug, defecated less, and shredded less paper* Many types of stimulation when applied during infancy have been shown to be effective i n altering later behavior* Q3ae effects of these various treatments are often quite diverse and there is no reason to assume that they are mediated by a similar mechanism* Clearly the preweaning period i s a stage when young rodents are extremely vulnerable to many varieties of en-vironmental influence* To what extent these early experience effects are direct results of the treatment and to what extent they are maternally mediated is d i f f i c u l t to determine, especially where' no observations of maternal behavior are made* With cage type, as with most early treatments, i t i s impossible to estimate 68 the relative rede of maternal mediation- With, fostering, however, the mother is the variable being manipulated; therefore any effects must be attributed solely to maternal influence- One can then attempt to isolate the c r i t i c a l aspects of the mother which are responsible for observed ef-fects on the offspring- This approach has characterized Denenberg* s work on rat-reared mice and differential handling by the two species of mother has been implicated as a crucial factor mediating the fostering effect, a l -though no comparison of maternal handling of mouse pups by rats and mice has yet been made-A similar comparison was not made i n the present study either but an observation by Kaplan and Hyland (1972) indicates that d i f f e r e n t i a l matern-al handling could be a factor mediating fostering effects i n gerbils- uiiey found that gerbil mothers rarely retrieved their pups, and pups which were out of the nest usually had to make their own way back- For rat mothers, however, pup-retrieving is a f a i r l y dominant response- Since strong evid-ence has been presented to implicate maternal manipulation as a mediator of early handling phenomena (Bell et a l -, 1971; B e l l e_t a l •, i n press), there i s good reason to suspect that i t may also be important i n other early ex-perience effects, including fostering' Now that i t i s established that fostering mice or gerbils to r a t mothers alters their respective behavior, more attention can be paid to exam-ining how these changes are mediated* In particular, detailed species com-parisons of maternal behavior and i t s effects on the young would seem to be the most f r u i t f u l approach to understanding hew fostering effects are med-iated as well as how the mother of a given species shapes the behavior of her own offspring* R3FER2NCES Ader, R. Adrenocortical function and the measurement of "emotionality." Ann- N*Y* Acad' Sc i * . 1969, 159, 791-805-Baran, D• and Glickman, S-E- "Ter r i t o r i a l marking" i n the Mongolian gerbil: A study of sensory control and function' J - Comp. Physiol-Psychol., 1970, 71, 237-245-B e l l , R.W-, Nitschke, W-, Be l l , NvT., and Zaehman, T-A. Maternal influences in early experience* Science, 1973 (In press). B e l l , H-W-, Nitschke, W-, Gorry, T-H-, and Zaehman, T«A. Infantile stimu-lation and ultrasonic signalling: A possible mediator of early handling phenomena. Develop. Psychobiol., 1971, 4, 181-191-Blum, S-L- and Thiessen, D-D- The effect of different amounts of androgen on scent marking in the male Mongolian gerbil. Hormones and Behav-, 1971, 2, 93-105-Broadhurst, P»L* Determinants of emotionality i n the rat* ]II Antecedent factors. Brit • J . Psychol. 1958, 49, 12-20-Bruell, J.H' Genetics and adaptive significance of emotional defecation i n mice. 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Androgen control of t e r r i t o r i a l marking in the Mongolian gerbil (Meriones unguiculatns)- Science, 1968, 160, 432-434-Thiessen, D.D., Owen, K», and Lindzey, G. Mechanisms of t e r r i t o r i a l mark-ing i n the male and female Mongolian gerbil (Meriones unguiculatus). J . Cbmp* Physiol. Psychol., 1971, 2Z» 38-47 • Thompson, R.W., and Lippman, L.G- Exploration and activity in the gerbil and rat, J- Comp• Physiol- Psychol*, 1972, 80, 439-448-Valle, F*p* Effects of strain, sex, and illumination on open-field be-havior of rats- Amer- J - Psychol-, 1970, 83, 103-111-valle, F.P> Rats* performance on repeated tests i n the open f i e l d as a function of age. Psychon* Sei., 1971, 23, 333-335-Valle, F-P- and Bols, R-J- Development of sex differences i n r a t s ' open-f i e l d , 1973, submitted f o r publication* Whimbey, A*E- and Denenberg, V.H> Two independent behavioral dimensions i n open-field performance. J - Comp* Physiol* Psychol., 1967, 63, 55-62. Winer, B.J. S t a t i s t i c a l Principles in Experimental Design* New York, McGraw-Hill, 1962-, 

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