American Journal of Primatology 1:401-412 (1981) Effects of Rearing on Aggression and Subordination in Papio Monkeys ANTHONY M. COELHO, JR. Primate Ethology Laboratory, Department of Cardiopulmonary Disease, Southwest Foundation for Research and Education, San Antonio, 7kxa.s CLAUD A. BRAMBLETT Department of Anthropology, University of l b r a s at Austin, Austin, %as The objective of this study is to assess the effects of short-term maternal deprivation (birth to 12 weeks) followed by peer group rearing on the development of aggressive and subordinate behaviors in papio monkeys (superspecies - Papio cynocephulus). Nursery reared monkeys (34 males and 30 females) were compared with mother-peer reared monkeys (11males and 12 females) in late infancy (6 to 12 months of age) and at the end of their juvenile stage (36 to 42 months of age) in social groups composed of 75% nursery reared subjects and 25% mother reared subjects. Focal animal data were analyzed with a repeated measure ANOVA model. In general, the nursery reared infants tended to be less aggressive than mother-peer reared infants and performed less dominance behaviors, such as displace. Significant sex differences were present in the perbehaviors. Signififormance of aggressive (u> Q ) and subordinate ( Q > u) cant age differences were observed, with infants having consistently higher rates of performance. Key words: aggression, baboons, behavior, maternal care, nursery care, rearing INTRODUCTION Ample evidence is available to demonstrate that rearing experiences have critical effects on behavioral development of some monkeys [Harlow & Harlow, 1965,1966; Kaufman & Rosenblum, 1969; Harlow et al, 1964; Mason 1968; Seay et al, 1964; Sackett, 1965; Sackett et al, 1967; Sackett & Ruppenthal, 1973; Schlottman & Seay, 19721. These studies clearly indicate that abnormal rearing of macaques produces inadequacies and abnormalities in their social and nonsocial behavior that are profound and last through adulthood [Cross & Harlow, 1965; Suomi et al, 1970; Mitchell, 1968, 1970; Mitchell et al, 1966;Sackett, 1965,1967,1969; Seay, 1966;Sackett & Ruppenthal, 1973; Ruppenthal et al, 19761. Extrapolating these findings to man, Sackett states that “similaritiesin Received February 18,1981; accepted June 13, 1981. Address reprint requests to Anthony M. Coelho, Jr., PhD, Primate Ethology Laboratory, Department of Cardiopulmonary Disease, Southwest Foundation for Research and Education, PO Box 28147, San Antonio. TX 78284. 0275-2565/81/0104-0401$03.50 0 1981 Alan R. Liss, Inc. 402 Coelho and Bramblett motor patterns between abnormal man and abnormal monkey suggest that the isolation reared monkey can serve as a model for the development of abnormal behavior in primates . ” Isolation is an extremely severe and abnormal rearing condition for any primate; therefore it is not too surprising that isolation reared individuals were affected by this experience. Two questions which are more relevant to the human condition are whether subtle abnormalities or differences in rearing produce differences in behavioral development and whether all species respond to rearing experiences in the same manner. Singh [1969,1977]studied the effects of rearingon behavior in urban dwellingMacaca mulatta and forest dwelling conspecifics. He demonstrated measurable differences between these groups in response to new stimuli and in aggression when they were housed under identical laboratory conditions. While the observed differences do not necessariIy reflect the effects of infant rearing practices, since urban and rural moneys were both raised by their mothers, the study does indicate that variability and plasticity exist in the normal behavioral responses by which a species is capable of successfully adapting to varied environmental and economic conditions. The degree to which theM. mulatta model can be generalized to other primate species has been questioned in studies by others [Seay et al, 1970; Rosenblum, 19711. Seay et al I19701 present data indicating that Cercopithecus patas I= Erythrocebuspatas) infants show few of the symptoms of maternal separation reported for M. mulatta Rosenblum presents data demonstrating some species variation in maternal separation responses within the genus Macaca. We compared the effects of early (birth to 3 months) experiences (nursery rearing and mother-peer rearing) on the behavioral development in late infancy (12 months of age) and at the onset of adolescence (42 months of age) in papio monkeys. The present study provides information on the sensitivity of papio monkeys to two different forms of subtle abnormalities (mother-peervs nursery rearing) in early rearing experience. We tested the hypothesis that differences in early rearing experiences (nursery and mother-peer rearing) would produce measurable differencesin the expression of aggressiveness (which occurs both in agonistic or hostile contexts and play contexts) and subordination. METHODS The data were obtained as part of a multidisciplinary longitudinal study of atherosclerosis risk factors. The project is multidisciplinary, but dietary and physiological variables were given priority in establishing the basic experimental designs. Monkey Subjects The 87 papio monkeys (45 males, 42 females)used in this study were born at Southwest Foundation for Research and Education (SFRE)in San Antonio, Texas of parents obtained as adults from several East African trapping sites. The parent breeding stock was housed in six one-male-multifemalesocial groups to insure information on the identity of each subject’s sire and dam. The parent population contained individuals who were phenotypically identifiable as yellow (Pc. cynocephalus) or olive (Pc. anubis) baboons. Three phenotypes are present in the study subjects with 23% of the subjects being yellow, 14%olive, and 63% hybrid mixed. Approximately 70% of the hybrid individcynocephalus) and olive dam (Re. uals are products of the crossing of a yellow sire (P.c. anubis). The three phenotypes are represented in approximately equal numbers in both sexes, both treatments and all four social groups. Design Procedures In the first phase (birth to 90 days of age) of the study (Table I) the subjects were assigned to mother-peer rearing (11males and 12 females) or nursery rearing (34 males and 30 females) by a randomization procedure which insured a balancing of the sires. Each dam is represented only once. In the second phase four peer-only social groups were established; each group contained approximately ?4mother-peer reared individuals and 403 Rearing, Aggression, and Subordination TABLE I. Number of Individuals in Each Cell of the Design* Social group Rearing Sex Mother-peer 11 cr 3 3 3 2 3 3 3 3 34 8 9 9 8 0 30 5 8 7 10 23 P 12 cr Nursery 64 *Design was identical for both age periods. 3/4 nursery reared individuals (TableI). Between 90 and 180days of age the subjects lived in one of four social groups, housed in the nursery in four large cages until they adjusted to a solid adult diet. These social groups were moved to large outdoor cages (15 x 7 x 8 m) where the subjects remained for the duration of the experiment. All behavioral measurements reported in this study were obtained on the subjects after they were 6 months of age and housed in large outdoor peer-peer social groups. Rearing Procedures Mother-peer rearing. At birth each of the molher-peer reared infants and its mother were moved from their home social group to a social group containing only mothers and infants, in a large outdoor cage identical in size (15 x 7 x 8 m) and adjacent to their original home cage. Although the mothers were drawn from separate socialgroups, they were not social strangers. The mothers were housed in adjacent cages and had interacted with each other through the large mesh chainlink cage walls and in most instances had previously been housed with each other in the years prior to their assignment to this project. During this treatment phase, the behavior of the mothers, who had been under observation for approximately 2 years [Bramblett, 19761, demonstrated no obvious behavioral change except for the lack of interactions with an adult male and performance of behaviors associated with motherhood. The mothers and infants remained in this social group until the infant was 90 days old. When the mother and infant were separated, the mother was returned to her original social unit and the infant was taken to the nursery for weaning and assignment to a peer-only social group consisting of nursery reared and mother-peer reared infants. Nursery rearing. At birth, the nursery reared infants were removed from their mothers and housed individually in a standard open sided wire nursery cage (51 x 56 x 61 cm) whcre they were able to see and hear all of the other nursery reared infants and touch infants housed on either side of them. Each cage was equipped with a large terry cloth towel (surrogate mother) to provide the infants with tactile security. The nursery reared infants were handled five times per day for bottle feeding by a nursery technician. Each day nursery reared infants spent approximately 2 to 4 hr in peer socializationgroups which took two forms. In the first, two to five nursery reared infants ( < 90 days of age) were placed together in larger nursery cages (1 x 1 x 1.3 m) for aL least 1 hr. In the second form, larger groups of 10 to 15 infants were allowed to interact in a 3 x 3 m room for at least 30 min. These nursery rearing procedures combine the best aspects of what Sackett and Ruppenthaldescribe as partial isolation, surrogate mothering, and peer rearing. 404 Coelho and Bramblett Data Acquisition The behavioral measurements were obtained by a pair of full time ethologists using focal animal sampling [Altmann, 19741 and diurnal scheduling [Bramblett & Coelho, 1975; Bramblett, 1976; Coelho & Bramblett, 1981aI. The ethologists maintained a 90% level of interobserver agreement throughout the study [Coelho and Bramblett, 1981bI. The 87 subjects were observed in a series of 10-min sampling sessions resulting in 350 hr of data and a total of approximately 2,100 focal animal sampling sessions. Thus each animal was sampled as a focal subject every 2 weeks for a total of 24 times. Each individual was sampled approximately 12 times when they were between 6 and 12 months of age (late infancy) and 12 times when they were between 36 and 42 months of age (late juveniles). The data obtained between 6 and 12 months of age were pooled into a single measure for each subject reflecting the late infancy age period. Similarly observations made between 36 and 42 months of age were pooled to produce a single measure for each subject reflecting a late juvenile or preadolescent behavioral measure. The data recording format was based on the question, “Who is doing what, to whom, for how long, how often, and in what sequence.” Using a Datamyte [Torgerson, 19773 the ethologists recorded all acts performed by or t o a focal subject. Each behavioral dataentry had the general format and structure of a sentence containing a subject (actor’sidentification code),verb (behavior),and object (recipient).The ethogram (or behavior inventory) used in this study was a molecular catalog of descriptions of 200 different terms for behaviors of papio monkeys [Coelho & Bramblett, 1981bl. We chose a molecular system [Sackett et al, 1978; Hollenbeck, 19781to record the behavior because it requiredless subjective interpretation on the part of the observer. Behavioral Measures We chose six of the most frequently observed aggressive and subordinate behaviors which occurred in both time periods as measures of the possible effects of rearing. Four of the behaviors, CHARGE, CHASE, HARD BITE, and HIT are expressions of aggression or threat and attack which may be used either in an agonistic (hostile)or play context. DISPLACE usually is used as a measure of an individual’s ability to dominate without physical attack or threat and AVOID is an expression of subordinance and deference. Each focal animal’s total performance, frequency of each behavior, was divided by the focal animal‘s total observation time in order to standardize the behavioral measures and express them as rate per hour. These rates constitute the measurements used in the analysis. Analysis of variance confirmed the lack of bias in the amount of sampling time by sex, rearing, and social group. Definition of Behavioral Measures: Charge. Rapid forward locomotion towards a recipient who is stationary. Chase. Rapid forward locomotion towards a recipient who is locomoting or fleeing. Hard bite. Clamping of the mouth with the teeth on the body of the recipient accompanied by a pain or fear response from the recipient. Hit. A slap or cuff. Displace. An actor supplants a recipient and occupies the space vacated by the recipient. Avoid. An attempt by an actor to deter physical contact with a recipient by withdrawing upon approach, leaning away, or detouring while locomoting. Data Analysis Each of the six behavioral measures were analyzed with a repeated measures model of analysis of variance [Winer, 19711. Repeated measures models are a special class of mixed models wherein repeated measurements are made of the same variable for each subject. The model makes a distinction between variables that classify the cases into groups (grouping factors) and repeated measures of the same variable (trial factor). In this sta- Rearing, Aggression, and Subordination 405 TABLE 11. Mean ActslHour Summary of Charge Behavior* Rearing Sex Mother-peer 1.56 (2.51) 2.13 (2.97) Infant 1.65 (2.91) Juvenile 0.48 (0.95) 2.99 (3.53) 1.27 (2.10) 1.52 12.48) (0.88) 1.86 (3.50) 0.39 (0.51) 0.97 (1.85) 0.29 (0.55) CT Q 0.99 (1.90) 0.46 W Nursery 0.88 (2.12) 1.13 (2.59) Q 0.63 (1.39) tistical procedure the grouping and trial factors are all fixed effect factors. The only random effect factor is the subject, and the subject is observed in all combinations of trial factors and at only one level of each grouping factor [Dixon & Brown, 1979,Winer, 19711. In the present study there are two measures for each subject's 6- to 12-monthperiod and 36- to 42-month age period for each behavior, thus the repeated measures ANQVA can be viewed as similar to a paired comparison t test. Effects of rearing condition, social group, sex, and age were considered in the study. Age period was the repeated measure. The design model included both main effects and interactions. All effects were considered fixed. Specific null hypotheses tested for each of the behavioral measures were the following: (1)H,: no difference between mother-peer and nursery reared; ( 2 )H,: no differences between sexes; ( 3 )13":no differences between age periods. Additionally, all interactions were tested. Significance level was set a P < .05 two tailed. RESULTS During the first 3 months of life, the nursery reared infants exhibited stereotypic behavioral abnormalities, such as autofellatio, depression postures, self clutching, continuous clutching and embracing of peers when in social groupings, sucking of hand or foot, a great deal of distress vocalization, and considerable responsiveness to humans. None of these abnormalities were ever observed in the mother-peer reared subjects either during the first 3 months of life or in subsequent months of their life. Some of the abnormalities such as self-clutching with simultaneous lip smacking and ear flatteninng occurred in nursery reared animals, even as late as 42 months of age, when their social groups were approached by humans, Mother-peer reared animals performed normal responses of ignoring, threatening, or avoiding approaching humans. Charge The overall mean performance rates for CHARGE are presented in Table 11. Males had significantly higher performance rates than females. Mother-peer reared subjects exhibited significantly higher performance rates than nursery subjects. Social group did not 406 Coelho and Bramblett TABLE 111. Mean ActdHour Summary of Chase Behavior* Infant 5.73 (7.13) Juvenile 0.79 (1.27) Rearing Sex Mother-peer 6.67 (8.65) 11.97 (9.67) 1.33 (1.33) P 2.88 (6.59) 6.26 (8.84) 0.49 (0.44) 6.12 (6.01) 0.99 (1.52) 3.17 (5.10) 0.45 (1.08) 0, 4.78 (4.80) ff Nursery 2.69 (4.62) 3.56 (5.06) 9 1.81 (3.90) demonstrate a significant main effect. Infants had significantly higher performance rates than juveniles. No significant interactions were detected. Chase Rearing effects were significant. Mother-peer reared individuals exhibited higher rates of CHASE behavior (Table111) than nursery reared individuals. Males had significantly higher mean values than females, and infants performed at significantly higher rates than juveniles. Significant interactions were present for age x rearing and age x sex. Mother-peer reared infant males had means that were considerably higher than either their female rearing mates or male and female nursery reared individuals (Table 111). There were no significant main effects of social groups. Hard Bite There were no statistically significant main effects for rearing, sex, or social group (Table IV). There were no statistically significant interactions. Infants, however, did have significantly higher mean performance rates than juveniles. Hit Rearing had a significant effect on performance of HIT (Table V). Mother-peer reared individuals had higher performance rates than nursery reared individuals. Males had significantly higher rates of performance than females and infants had significantly greater mean values than juveniles. No significant main effects were detected for social groups and no significant interactions were detected. Displace The overall mean performance rates of DISPLACE behavior are presented in Table VI. ,Mother-peer reared subjects had significantly higher values than nursery reared subjects. Males had significantly higher values than females and infants had significantly higher values than juveniles, The social group’s main effect was significant. Social groups 2 and 4 exhibited higher rates of DISPLACE behaviors than groups 1 and 3. All interactions were significant. Mother-peerreared infant males in groups 2 and 4 had mean DISPLACE rates that were considerably higher than other subjects. Mother-peerinfant females in social groups 2 and 3 had mean DISPLACE values that were greater than Rearing, Aggression, and Subordination 407 TABLE IV. Mean ActslHour Summary of Hard Bite* Infant 0.62 (1.39) Juvenile 0.18 (0.29) 0.87 (1.13) 1.41 (1.37) 0.33 (0.35) 9 0.32 10.38) 0.46 (0.45) 0.18 (0.24) 0.46 (0.65) 0.23 (0.30) 0.58 (2.07) 0.08 (0.24) Infant 1.49 11.61) Juvenile 0.33 (0.49) Rearing Sex Mother-peer 0.60 (0.86) W cr Nursery 0.34 11.08) 0.35 (0.51) 0 0.33 (1.48) *(SD). TABLE V. Mean ActslHour Summary of Hit Behavior* Rearing Sex Mother-peer 1.26 (1.76) 1.58 (1.46) 2.59 (1.39) 0.56 (0.53) P 0.93 (1.97) 1.58 (2.66) 0.29 (0.36) 1.64 (1.39) 0.37 (0.52) 0.87 (1.11) 0.20 (0.47) 0- 0- Nursery 0.78 (1.11) 1.01 (1.22) P 0.54 (0.91) other females. As in the previous behaviors, infant means were greater than juvenile means. Avoid Females had significantly higher mean rates of AVOID (Table VII) interactions than males. No significant main effects of rearing or social group were detected. Subjects exhibited significantly higher rates of AVOID as infants than as juveniles. No significant interactions were detected. 408 Coelho and Bramblett TABLE VI. Mean ActslHour Summary of Displace Behavior* Social group Rearing Sex Age 1 1.30 (1.87) 2 1.56 (2.27) 3 0.73 (1.32) 4 1.63 (3.32) 1.91 (3.30) 4.92 (5.65) 1.59 (1.57) 14.07 (9.07) 1.38 (0.43) 2.55 (2.49) 1.35 (0.92) 1.73 (0.52) 0.57 (0.63) 3.86 (4.13) 2.45 (4.24) 1.44 (2.28) 0.33 (0.58) 0.57 (0.49) 0.82 (0.92) 0.68 (0.79) 2.50 (2.70) 1.52 (1.38) 0.78 (1.11) 1.41 (1.57) 1.65 (1.82) 1.27 (1.08) 0.26 (0.41) 0.79 (0.80) 0.50 (0.89) 0.83 (1.80) 0.36 (0.49) 1.27 (2.29) 0.23 (0.51) 0.56 (0.83) 0.21 (0.37) 0.65 (0.74) Infant 0 4.85 (6.33) 3.30 (4.74) Juvenile Mother-peer 1.75 (1.32) 2.28 (3.75) Infant P 1.34 (2.25) 2.08 (3.00) Juvenile 0.60 (0.64) Infant 0 1.53 (1.79) 1.25 (1.54) Juvenile 0.99 (1.20) Nursery 0.96 (1.44) Infant P 0.63 (1.26) 0.81 (1.64) Juvenile 0.41 (0.66) *(SD). DISCUSSION Normal rearing conditions are definable as the basic ontogenetic conditions under which the species evolved to its present form. In most primates these conditions include membership in a stable social group containing individuals of both sexes and all ages, (2) the membership of the group contains some individuals with close genetic relationships such as sibs and progeny, and (3) care, handling, and interaction with conspecific guardians (mothers and others) and role models. I t is obvious that in this study we have compared animals exposed to two different forms of abnormal rearing. Mother-peer rearing is more like the normal condition defined above than the nursery rearing condition. Rearing Effects and Limitations The rearing treatment is somewhat confounded by the fact that nursery reared subjects were housed in cages that are much smaller than the cages of mother-peer reared subjects. These conditions were the result of the fact that the overall dietary and physiological portions of the multidisciplinary experiment were given priority in establishing protocol and it was neither economically realistic to house the nursery animals like the Rearing, Aggression, and Subordination 409 TABLE VII. Mean ActslHour Summary of Avoid Behavior* Rearing Sex Mother-peer 8.75 (7.62) Infant Juvenile 12.07 (8.53) 7.24 (5.49) 12.23 (8.75) 5.28 (4.35) 15.91 (11.16) 8.47 (6.53) 11.17 (8.55) 5.23 (3.88) 11.48 (7.18) 9.75 (6.02) 0 10.48 (8.85) 9 12.19 (9.71) 0 Nursery 9.41 (7.03) 8.20 (7.23) Q 10.62 (6.63) *(SD). mother-peer subjects, nor was it physically possible to house the mother-peer subjects in the small nursery cages. Thus, while it is possible that the nursery caging conditions, that were necessary for the dietary treatments, may have effected behavior, we feel that it is unlikely. Recent studies by Coelho and Bramblett [1981a]and Elton demonstrate that baboon behavior does not appear to be affected by cage size unless the animals are subjected to extreme social crowding conditions which were not a characteristic of this study. This study demonstrates that there are consistent differencesbetween mother-peer and nursery reared papio monkeys. Even a short-term rearing difference of 3 months produces effects which are present in late infancy and persists to the late-juvenile-preadolescent period. Our data clearly indicate that nursery reared subjects were much lower than motherpeer reared subjects in performance of dominance type behaviors and showed no difference in performance of AVOID. These two behaviors suggest that the nursery reared individuals are socially inept because on the basis of previous work with six other social groups of normal baboons reared in the wild [Bramblett, 19761we expected that individuals who did not have high performance values for DISPLACE would have high values for performance of AVOID. This is not the case in the nursery reared subjects. One explanation for the very high rates of DISPLACE behavior in social group 4 mother-peer reared males (Table VI) may be the inability of the nursery reared individuals in that group to recognize and interpret subtle social situations and to behave appropriately. This inability may be the result of not learning the appropriate behavioral response or of a disruption in the development of processes which produce the capacity for behavioral responses. Failure of subordinates, or social group members in general, to perform appropriate responses to subtle communicative gestures may result in increases in aggressive behavior performance by the dominant animal, either in terms of frequency or intensity, in order to reassert the social order. An additional factor that enters into this performance difference between nursery and mother-peer reared subjects is the possibility that the performance rates of the motherpeer reared subjects are higher than rates performed by normally reared subjects. It is possible that being separated from their mothers at 12 weeks of age results in increases 410 Coelho and Bramblett in subsequent aggressiveness. However, this does not explain the failure of nursery reared subjects to demonstrate the normal subordinate behaviors in response to aggression directed at them. Sex Differences This study clearly demonstrates that very consistent sex differences are present in papi0 monkeys in late infancy in the performance of aggression and subordinance. Males were consistently more aggressive and had higher mean performance rates for displacement, while females had higher rates of avoidance. These findings are in agreement with previous studies of macaques which report early development of sexual dimorphism in these behaviors, as well as with anecdotal reports by researchers working with Pupio sp. [DeVore, 1963; Kummer, 1968; Ransom & Rowell, 19721. Our observation of the subjects left us with the subjective impression that the effects of nursery rearing were qualitatively more devastating initially and longer lasting in males than females. For example, male nursery reared subjects were the individuals who habitually performed self-clutching and simultaneous lipsmacking and ear flattening in response to human approach. Mother-peer reared males were never observed to perform these behaviors. Female nursery reared subjects were less predictable in the performance of these abnormal behaviors. Social Group Our findings of no differences in most cases with respect to social groups was not surprising since the social groups were designed to be almost identical in all respects. These findings confirm a previous study [Bramblett, 19761 of the sires and dams of our study subjects that indicates that when age, group size, and group composition are similar, there are no group differences in the mean rate of behavior performance. The one exception (DISPLACE)reported in this paper probably reflects personality differences, either innate or as a result of ontogenetic experience, which affected a facet of social behavior that was particularly sensitive to these types of differences. Age The consistently higher performance rates in the infant period as compared with the juvenile period reflects a general maturational trend of change in the context and consequence of aggression. During infancy, aggression occurs largely in a “play”context. Infant animals lack the anatomy to inflict serious injury. As the animals grow and develop their social skills, they also become increasingly capable of inflicting or receiving serious physical injury as a result of increasing strength and dental anatomy. A consequence of this is a greater reliance on nonphysical communicative signals and a general reduction in interaction under conditions of stable social group composition. As long as the social structure and organization remain stable, there is little need for continual physical testing and physical assertiveness such as CHASE, CHARGE, BITE, and HIT. SUMMARY Our study demonstrates that papio monkeys are sensitive to subtle short-term differences in rearing when measured in terms of the performance of aggressiveness such as CHARGE, CHASE, BITE, and HIT, as well as performance of dominance behaviors such as DlSPLACE. Nursery rearing with peers, surrogate mother, and visual and vocal communication failed to produce subjects comparable to mother-peer reared individuals. The rearing effects were present in infancy and persisted through the entire juvenile period up to adolescence. These inadequacies are serious in so far as the aggressive behaviors are instrumental in contributing to an individual’s success in a social group both in terms of the benefits of group membership and perhaps future reproductive success. Rearing, Aggression, and Subordination 411 ACKNOWLEDGMENTS We acknowledge Drs. H.S. Wigodsky, C.A. McMahan, and H.C. 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