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The ability to quickly perceive others' rank minimizes costs by helping individuals behave appropriately when interacting with strangers. Indeed, humans and at least some other species can quickly determine strangers' rank or dominance based only on physical features without observing others' interactions or behavior. Nonhuman primates can determine strangers' ranks by observing their interactions, and some evidence suggests that at least some cues to dominance, such as facial width‐to‐height ratio (fWHR), are also present in other primates. However, it is unknown whether they can determine strangers' rank simply by looking at their faces, rather than observing their interactions. If so, this would suggest selective pressure across the primates on both cues to dominance and the ability to detect those cues accurately. To address this, we examined the ability of male and female tufted capuchin monkeys (Sapajus [Cebus] apella) to categorize images of the faces of unknown conspecifics (Sapajus from different colonies) and humans (computer‐generated and real) as dominant or nondominant based only on still images. Capuchins' categorization of unknown conspecific faces was consistent with fWHR, a cue to dominance, although there was a strong tendency to categorize strangers as dominant, particularly for males. This was true despite the continued correct categorization of known individuals. In addition, capuchins did not categorize human strangers in accordance with external pre‐ratings of dominance by independent human raters, despite the availability of the same cue, fWHR. We consider these results in the context of capuchin socio‐ecology and what they mean for the evolution of rapid decision‐making in social contexts. Research Highlights: Tufted capuchins categorize unknown male faces as dominant or not consistent with facial width‐to‐height ratios.Categorizations are biased toward dominance, suggesting that all strangers are initially treated as a threat.This suggests that capuchins do best by assuming dominance in unknown males. [ABSTRACT FROM AUTHOR]

Facial expressions are key to navigating social group life. The Power Asymmetry Hypothesis of Motivational Emancipation predicts that the type of social organization shapes the meaning of communicative displays in relation to an individual's dominance rank. The bared‐teeth (BT) display represents one of the most widely observed communicative signals across primate species. Studies in macaques indicate that the BT display in despotic species is often performed unidirectionally, from low‐ to high‐ranking individuals (signaling submission), whereas the BT display in egalitarian species is usually produced irrespective of dominance (mainly signaling affiliation and appeasement). Despite its widespread presence, research connecting BT displays to the power asymmetry hypothesis outside the Macaca genus remains scarce. To extend this knowledge, we investigated the production of BT in relation to social dominance in dyadic interactions (N = 11,377 events) of 11 captive bonobos (Pan paniscus). Although adult bonobos were more despotic than previously suggested in the literature, BT displays were produced irrespective of dominance rank. Moreover, while adults produced the BT exclusively during socio‐sexual interactions, especially during periods of social tension, immature bonobos produced the BT in a wider number of contexts. As such, the results indicate that the communicative meaning of the BT display is consistent with signaling appeasement, especially in periods of social tension. Moreover, the BT display does not seem to signal social status, supporting the prediction for species with a high degree of social tolerance. These results advance our understanding of the origins of communicative signals and their relation to species' social systems. Research Highlight: Adult bonobos use bared‐teeth (BT) displays irrespectively of dominance rank, during sexual behaviors, when tensions are high.Juvenile bonobos use the BT in wider contexts, suggesting an adjustment of display rules over bonobo development. [ABSTRACT FROM AUTHOR]

Strong, stable social bonds in primates are characterized by high levels of social affiliation, low levels of aggression, minimal stress, and affiliative reciprocity within the dyad. In relatively well‐studied catarrhine monkeys, these bonds tend to form most frequently between kin, animals close in age, and animals close in rank. This results in patterns of affiliation in which kin, similarly aged animals, and like‐ranked animals tend to affiliate and patterns of aggression and submission where animals tend to aggress more toward nonkin and closely ranked animals, and submit more toward distantly ranked animals. However, literature on how affiliative and agonistic relationships are organized in platyrrhine primate species like brown capuchin monkeys is limited and conflicting. In this study, we used social network analyses to characterize how age, sex, maternal kinship, and dominance rank relate to the patterns of submissive, aggressive, contact, and grooming interactions in a group of captive brown capuchin monkeys. Like catarrhine monkeys, brown capuchin monkeys showed a steep linear dominance hierarchy, tended to affiliate with kin, similarly aged animals, and like‐ranked animals, and tended to aggress more toward nonkin. However, our monkeys showed a pattern of affiliation and grooming down the hierarchy that is inconsistent with grooming up the hierarchy patterns often seen in catarrhine monkey groups, suggesting that brown capuchins do not compete for access to higher ranking social partners. Higher ranking monkeys were most central to the aggression network, and lower ranking monkeys were most central to the submission network. Mid‐ranking monkeys were the most central to the contact network, suggesting that they may play an important role in the affiliative cohesion of the group. These results inform our understanding of brown capuchin social behavior specifically, and of how demographic factors relate to social organization in platyrrhine primates generally. Highlights: Captive brown capuchins show a steep linear dominance hierarchy.Rank differentially predicts who is the most central across networks: High‐rankers for aggression, low‐rankers for submission, & mid‐rankers for contact.They affiliate with kin, similarly aged and like‐ranked animals, & aggress to nonkin. [ABSTRACT FROM AUTHOR]

Play is widespread across mammalian taxa, but species strongly vary in the ways they play. In less despotic primate species (i.e., with less steep dominance hierarchies, less severe conflicts, and more reconciliation), play has been described as being more frequent, cooperative, and freely expressed. To study the link between social play and dominance style, we compared play behavior in free‐ranging infants, juveniles and subadults of more despotic Japanese macaques (Macaca fuscata, N = 24) and less despotic moor macaques (Macaca maura, N = 17). We found interspecific differences in play behavior that corresponded with the contrasting dominance styles of the study species, largely confirming our predictions. In particular, moor macaques spent a larger proportion of time in solitary and social play than Japanese macaques, while Japanese macaques spent a larger proportion of time in grooming interactions. In moor macaques, play sessions included more players, a larger variety of play behaviors, greater play face rates, a greater proportion of time in contact play, and a higher rate of reciprocal play‐biting than in Japanese macaques. Aggressive escalations were not common, but more frequent in Japanese macaques. Finally, a higher frequency of play faces during play sessions predicted the occurrence of more reciprocal play‐bites, but not the proportion of time spent in contact play behaviors. Additional studies on other groups and species will allow a better understanding of the link between dominance style and social play. [ABSTRACT FROM AUTHOR]

In captivity, male bonnet macaques ( Macaca radiata) frequently express 'friendship' toward one another, including affiliative behavior such as huddling, grooming, coalitionary support, and sitting in close proximity. The purpose of this study was to determine whether wild adult male bonnet macaques also express 'friendship' by investigating whether or not (1) adult male bonnet macaques have affiliative social relationships with other males, (2) the strength of social relationships varies among dyads, (3) there is time-matched reciprocity in allogrooming among dyads, and if so, whether the level of reciprocity occurs within a bout of grooming, a day, or over 2 months (the limit of this study), and (4) a correlation exists between the strength of social relationships and dominance ranks among adult males. Focal samples totaling 150 hr on all seven adult males in one study group were conducted to record both agonistic and affiliative interactions. Agonistic interactions were used to construct a dominance hierarchy, whereas affiliative interactions (sitting in proximity to within 1 m with and without grooming) were used to quantify the existence and strength of social bonds within dyads. Results show that adult male bonnet macaques had differentiated affiliative relationships with other males in their group. There was little reciprocity of grooming within a bout of grooming or within a day, but greater reciprocity over the study period of 2 months. There was no correlation between dominance ranking distance and the strength of affiliative relationship within dyads; however, within dyads lower-ranking males groomed higher-ranking males more than vice versa. This study suggests that friendships in male bonnet macaques are characterized not by immediate tit-for-tat reciprocal altruism, but by reciprocity over a longer time span, and that affiliative social relationships may be less constrained by agonistic relationships than is the case in more despotic species of macaques. Am. J. Primatol. 73:1107-1113, 2011. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Suitable sleeping sites as potentially restricted resources are suggested to shape sociality in primates. We investigated sleeping site ecology of a rain-forest dwelling sportive lemur in eastern Madagascar for the first time. Using radiotelemetry, we characterized the type, quality and usage of sleeping sites as well as social sleeping habits of 11 focal individuals of the weasel sportive lemur (Lepilemur mustelinus) during the dry and the onset of the rainy season. Morphometric measurements provided additional information. The sexes showed an unusual sexual dimorphism for primates. Males and females did not differ in body length, but females surpassed males in body mass suggesting female dominance. Both sexes used dense vegetation and holes in hollow trees high above the ground as shelters for sleeping during the day. No sex difference in the quality of tree holes was found, but focal individuals used tree holes more often than open sleeping sites in dense vegetation. Both sexes showed high sleeping site fidelity limited to two to six different sites that they used primarily solitarily. The results imply that suitable sleeping sites are limited and survival of this species will strongly depend on the availability of mature rain forests with suitable hollow trees. Furthermore, these findings provide evidence of a solitary sleeping and ranging system in this rain-forest dwelling sportive lemur with suitable sleeping sites as defendable resources. Am. J. Primatol. 70:247–253, 2008. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Adult females in a female-bonded, cercopithecine species such as baboons are characterized by hierarchically ranked matrilines, i.e., female offspring assume rankings just beneath those of their mothers. In this system of closely ranked matrilines, a female should engage in significantly more affiliative interactions with those individuals who are closely ranked to herself than with those individuals who are more distantly ranked. We examine the hypothesis that females in this troop of feral yellow baboons (Papio hamadryas cynocephalus ) who are closely ranked will also show close social affiliation. We collected focal data on 23 feral, adult female subjects (253 possible dyads) over approximately 1 year at the Tana River National Primate Reserve, Kenya. Following Bramblett's [Behav Brain Sci 4: 435, 1981] method of dominance tabulation and utilizing a modified version of Smuts' [Sex and friendship in baboons, Hawthorne: Aldine Publishing Co., 1985] preferred partner index, we describe and compare the dominance matrix and hierarchy, preferred proximity partner and grooming partner sociograms, and the social networks of these 23 focal females. Over 1,400 interactions were utilized in the dominance tabulations, 41 statistically significant proximity partner preferences were documented, and 100 grooming dyads were recorded. We examine both partners' ranks and the presence of an infant as possible factors influencing proximity and grooming partner preferences. We find that in this population there is no direct correspondence between females' ranks and their affiliation partners. Neither proximity nor grooming preferences are consistently predictable from partners' ranks. While proximity preferences were not significantly influenced by the presence of an infant, grooming partner preferences were. Females with infants had more grooming partners and were more often involved in unidirectional grooming relationships as the recipients than were females without infants. We conclude that females' dominance rankings are not good predictors of either proximity partner or grooming partner preferences and that the presence of an infant does have a significant impact on grooming partner preferences in this population. Am. J. Primatol. 47:321–334, 1999. © 1999 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Social peer groups of callitrichid monkeys [marmosets and tamarins] exhibit intrasexual dominance hierarchies in captivity. This laboratory study employed two-choice behavioral discrimination bioassys to test the hypothesis that scent from female common marmosets contains chemical cues that permit discrimination between dominant females in the peri-ovulatory versus luteal phase of the ovarian cycle and females holding dominant versus subordinate status. When scent from only dominant females was presented, marmosets directed significantly greater amounts of investigatory behavior toward peri-ovulatory scent versus scent collected during the luteal phase of the ovarian cycle. Animals of both sexes demonstrated significant discriminatory behavior between scent deposited by dominant versus subordinate females, but only when the dominant female was in the peri-ovulatory phase of the ovarian cycle. Test animals directed equal amounts of investigative behavior toward scent from luteal-phase dominant females and subordinate females. Female test subjects deposited significantly more scent marks over presented scents than did male subjects, particularly when the scent had been donated by a peri-ovulatory female. Chemical odors specific to the peri-ovulatory and luteal phases of the ovarian cycle may play a role in mediating behavioral interactions among marmosets. Am. J. Primatol. 46:265–284, 1998. © 1998 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

This paper reports a study designed to test the hypothesis that a relationship exists among dominance rank, tension, and scratch behaviors in anubis baboons (Paplo cynocephalus anubis), Our study was conducted on two groups of male baboons, each containing eight unrelated individuals who were approximately 6 years of age and who shared common rearing histories. Focal animal sampling was used to collect behavioral data. Hand scratching, foot scratching, avoid, tension, allogrooming, autogrooming, and manipulation were measured as acts performed per hour of sampling. Dominance matrices were constructed based on net difference of avoid behavior performed and received (adjusted for time sampled). Individual status ranks were grouped into two status classes, high and low. Analysis of variance models demonstrated significant differences in the performance rate of scratching behaviors by dominance rank class, as well as differences in scratching performance by tension class. Individuals in the high status class had significantly higher rates of total scratching, hand scratching, foot scratching, and tension behavior performance than their counterparts in the low status class. No significant difference was found between status classes or tension classes for performance rate of allogrooming, autogrooming, or manipulation behavior. The frequency of scratching and general level of activity were not significantly correlated. The results are interpreted to indicate the possibility that scratching may function as a displacement behavior, which subjectively appears to communicate heightened frustration, anxiety, or arousal. [ABSTRACT FROM AUTHOR]

This paper summarizes results of simulation analyses aimed at elucidating the way in which two important dimensions of female rank orders-nepotism and age-gradedness--are affected by variation in individual strategies of rank acquisition on the one hand and by variation in population-wide demographic parameters (eg, birth rate, death rate, etc) on the other. Female rank orders in simulated primate groups were characterized by substantial variability on a year-to-year basis in both nepotism and age-gradedness owing to stochastic processes alone. Although, in general, groups characterized by strongly nepotistic rank orders were not also strongly age-graded, quantitative measures of these two rank-order dimensions for individual groups showed little stability over intervals of time exceeding 3 years. Surprisingly, changes in birth and death rates did not strongly affect either nepotism or age-gradedness so long as average group size remained constant. However, in populations characterized by expanding or declining group size, variation in demographic parameters did indeed exert a powerful influence on the structure of female rank orders. Both nepotism and age-gradedness were also strongly affected, and in quite different ways, by changes in the rules of rank acquisition by females. In sum, the present analyses suggest that differences between species in the degree of nepotism and age-gradedness characteristic of their female rank orders does not in and of itself constitute evidence that the females of those species use markedly different strategies of rank acquisition. [ABSTRACT FROM AUTHOR]

A simple measure of relative dominance status (cardinal rank.) is described which we have termed the dominance index. Like more familiar techniques for assessing rank order, it is based on the direction of aggressive and submissive behaviors between all possible paired combinations of animals in a social group. Using data from five groups of female rhesus monkeys, it reliably produced the same ordinal ranks as fight interaction matrices. There was also good agreement with the cardinal ranks produced by two additional measures of dominance and with those produced by observer ratings. The dominance index can be calculated when fights have not actually occurred and is largely independent of the frequency of agonistic interactions. It has, therefore, wide application and can estimate dominance during brief sampling periods (one hour) and also in stable groups when agonistic interactions are low. Its application is described in experiments in which the male in a group of females was changed and the hormonal status of the females was altered. Estrogen increased female dominance status relative to other females. [ABSTRACT FROM AUTHOR]

Observations of social behavior in 120 pairs of rhesus macaques were organized into three matrices: male-male interactions, female-female interactions, and male-female interactions. The alternating least-squares dimensional analysis (ALSCAL-4) was applied to each matrix to derive one-, two-, three-, and four-dimensional solutions. For each matrix, the two-dimensional solution gave the best fit with least stress. The loadings for each category on the two dimensions were then compared with previously derived message statements for those categories and the messages were corrected as needed to conform to these analyses. For all three matrices, the two dimensions underlying social behaviors were dominance or submissiveness by the self, and a positive or negative affiliative relationship bias to the pairmate. [ABSTRACT FROM AUTHOR]

Eight and a half years of dominance relations within a captive group of patas monkeys were analyzed. It was found that matrilineal kinship significantly influenced individuals' ranks. In contrast, with the exception of certain intramatriline changes, increasing age had no predictable effect on overall rank, at least for females (this was untestable for males). Offspring typically challenged maternal dominance and in eight of twelve dyads, offspring either rose fully over their mothers (three cases, all daughters) or at least achieved dominance ambiguity with them. Additionally, two of the four younger sisters with an opportunity to rise in rank over an older sister did so. The group dominance hierarchy was unstable for 75% of the study due to a combination of agonistically induced and demographically induced rank changes. Concentration of the highest ranks in a single matriline showed a stronger association with group hierarchy stability than did the presence of an adult, nonnatal male. Group hierarchy stability was associated with increased affiliation (sitting close and sitting touching), but otherwise there were no behavioral correlations. Individuals' ranks within the group hierarchy were unrelated to their chances of being wounded or having diarrhea. Adult females' ranks were over twice as stable as the group hierarchy (57.1% stability), but stability/instability was not correlated with any behavioral changes. Available evidence suggests that dominance relations play only a minor role in the organization of patas monkeys' intragroup behavior. Am. J. Primatol. 42:41–51, 1997. © 1997 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

We have previously studied the relationship between social subordinance (by approach-avoidance criteria) and physiology among male olive baboons (Papio anubis) living freely in a national park in Africa. In stable hierarchies, subordinate individuals have elevated basal glucocorticoid concentrations and a blunted glucocorticoid response to stress, as well as a prompt suppression of testosterone concentrations during stress. These facets have been interpreted as reflecting the chronic stress of social subordinance. In the present report, we find that these endocrine features do not mark all subordinate individuals. Instead, endocrine profiles differed among subordinate males as a function of particular stylistic traits of social behavior. A subset of subordinate males was identified who had significantly high rates of consortships, a behavior usually shown only by high-ranking males. Such behavior predicted the beginning transition to dominance, as these males were significantly more likely than other subordinates to have moved to the dominant half of the hierarchy over the subsequent 3 years. In keeping with this theme of emerging from subordinance, these individuals also had significantly larger glucocorticoid stress-responses, another feature typical of dominant males. However, these subordinate males also had significantly elevated basal glucocorticoid concentrations; it is suggested that this reflects that stressfulness of their overt and precocious strategy of reproductive competition. In support of this, subordinate males with high rates of covert “stolen copulations” did not show elevated basal glucocorticoid concentrations. A second subset of subordinate males were the most likely to initiate fights or to displace aggression onto a third party after losing a fight. These males had significantly or near-significantly elevated testosterone concentrations, compared to the remaining subordinate cohort. Moreover, these males had significantly lower basal glucocorticoid concentrations; this echoes an extensive literature showing that the availability of a displacement behavior (whether aggressive or otherwise) after a stressor decreases glucocorticoid secretion. In support of this interpretation suggesting that it was the initiation of these aggressive acts which attenuated glucocorticoid secretion, there was no association between glucocorticoid concentrations and participation (independent of initiation) in aggressive interactions. Thus, these findings suggest that variables other than rank alone may be associated with distinctive endocrine profiles, and that even in the face of a social stressor (such as subordinance), particular behavioral styles may attenuate the endocrine indices of stress. Am. J. Primatol. 42:25–39, 1997. © 1997 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Dispersals by subadult or adult male baboons are common. In contrast, the occasional transfer of aged baboons is puzzling, given the physical dangers of transfer and the cognitive demands of mastering the ecological and social rules of a new troop. The present data suggest a possible explanation for such transfers in a study of two troops of olive baboons (Papio anubis) in Kenya. Aged males who remained in the troop in which they had been dominant were subjected to significantly higher rates of approach-avoid interactions by the current high-ranking cohort (i.e, the individuals they had dominated years past) when compared to males who had transferred into the troop m their old age. Thus, transfer in old age offers the advantage of relative anonymity. Of the 14 males who progressed into older adulthood in the same troop in which they were in their prime, seven ultimately transferred to a different troop. The seven who remained and the seven who transferred did not differ in the rate at which they were subjected to approach-avoid interactions. However, those who remained had significantly higher rates of venous affiliative behaviors (copulations, consortships, grooming and contact with females, and positive interactions with infants). Thus, amid the disadvantages of an old age spent in the troop in which a male baboon was in his prime, a high degree of social affiliation might constitute a sufficient disincentive against transferring. [ABSTRACT FROM AUTHOR]

Agonistic interactions and postconflict behavior of moor macaques (Macaca maurus) were studied in their natural habitat, South Sulawesi, Indonesia. Individuals were involved in 0.28 agonistic interactions per hour. Forty-two percent of agonistic interactions were followed by affiliative contacts between the former opponents. Such affiliative contacts occurred within 2 minutes of the agonistic interaction and were most often initiated by the victim's approach to the aggressor. The most common postconflict behavior was grooming of the aggressor by the victim. The present study provides further evidence of a positive correlation between a high tendency for postconflict affiliative contact and a relaxed dominance style. Captivity might not alter the expression of postconflict behavior. The present study suggests that it is possible to demonstrate the occurrence of reconciliation a posteriori by using data obtained by general focal observation protocols. [ABSTRACT FROM AUTHOR]

In the present study, we seek to relate dominance style with group cohesion in a captive group of Japanese macaques (Macaca fuscata). Social data were gathered on approach rate, result, and direction, aggression rate and intensity, grooming rate and direction, and conciliatory tendency. Data were collected using focal animal sampling and instantaneous scan sampling. Reconciliation data were collected using ad libitum observations of aggression with ten-minute post-conflict and matched-control focal observations. Data were compared to prior studies on rhesus (M. mulatta) and stumptail macaques (M. arctoides) living in similar environments. Each species demonstrated the presence of a formalized dominance hierarchy based on the teeth-baring display. The Japanese macaque group showed a lower rate of approach with a higher proportion of negative outcomes than either of the other species. Rates of aggression and reconciliation were also lower in the study troop, suggesting a strict hierarchy while maintaining an optimal nearest-neighbor distance. Overall, this group of Japanese macaques was less sociable than other groups of the same species, perhaps due to a history of individual removals. [ABSTRACT FROM AUTHOR]

In a population of wild baboons living in East Africa, we have observed endocrine differences among individuals as a function of dominance rank. Among these differences, we previously observed indirect evidence for dominant males being more responsive to sympathetic catecholamines than were subordinate males. The present report tests this explicitly. Male baboons of known rank were anesthetized, and sympathetic and parasympathetic activity was pharmacologically inhibited. In experiment I, males were challenged with epinephrine; over a wide dose range, dominant males had the largest and fastest rises in systolic pressure, the greatest peak systolic pressure, and the most rapid recovery from the epinephrine challenge. Similar rank-related differences in heart rate response to epinephrine also occurred. Experiment II showed that this phenomenon probably reflects rank-related differences at both the heart and vasculature. As evidence, the same rank differences in systolic blood pressure responsiveness occurred when males were challenged with the alpha receptor agonist phenylephrine (which predominantly constricts systemic veins and arterioles), while the same rank differences in heart rate responses occurred following stimulation with the beta receptor agonist isoproterenol (which selectively works at the heart). These data were obtained from animals stressed by anesthetization, known to cause considerable glucocorticoid secretion in this population. Such steroids are well known for their capacity to augment catecholamine action. In experiment III, we blocked endogenous glucocorticoid secretion with the steroidogenesis inhibitor metyrapone, and repeated the epinephrine challenge. Under these conditions, the rank differences in epinephrine responsiveness were eliminated. Thus, dominant males are not so much preferentially sensitive to catecholamine action, as much as to the potentiating effects of glucocorticoids upon such action. [ABSTRACT FROM AUTHOR]

We have previously studied the relationship between dominance rank and physiology among male olive baboons (Papio anubis) living freely in a national park in Africa. In stable hierarchies, such males have distinctive secretory profiles of glucocorticoids and of testosterone. We find that these endocrine features are not, in fact, purely markers of social dominance; instead, they are found only among dominant males with particular stylistic traits of social behavior. One intercorrelated stylistic cluster revolved around the intensity with which the male is involved in sexual consortships (e.g., frequency of copulation, of grooming, degree to which feeding is suppressed by being in consortship). Males most involved in such consortships had the lowest basal cortisol concentrations and smaller cortisol stress-responses. A second stylistic cluster revolved around the degree of social affiliation (e.g., rate of grooming and interacting positively with non-estrus females and infants). Males who were highly affiliated had low basal cortisol concentrations and an attenuated cortisol stress- response. A third cluster revolved around the degree to which males could distinguish between highly threatening interactions with rivals and neutral or mildly threatening ones. Males most adept at this had lower basal cortisol concentrations. These behavioral/endocrine clusters were independent of each other. This suggests that the same adaptive physiological feature (e.g., low basal cortisol concentrations) may arise from different and independent personality styles. [ABSTRACT FROM AUTHOR]

The relationship between social status and telemetrically recorded heart rate (HR) was studied among 29 adult male cynomolgus monkeys (Macaca fascicularis) which had been maintained in six social groups (n = four or five) for 26 months. The membership of each group was reorganized periodically (20 times in 26 months) by shifting monkeys from group to group in a way that maximized each animal's exposure to social strangers. The social behavior of all animals was monitored, via focal sampling, twice per week: social status was based on the outcome of agonistic encounters and was determined every 2 weeks. For four nights on each of two occasions (months 13 and 25 of the experiment), the HRs of all animals were sampled 12 times per hour, 30 seconds per sample between 1800 h and 0900 h. A more limited nocturnal HR sampling was performed during the first month of the experiment. The behavioral observations revealed that, despite the repeated social reorganization, some monkeys were habitually dominant in their groups while others were consistently subordinate. Further, those monkeys falling above the median in dominance status had significantly lower HRs than their subordinate counterparts (104 vs. 117 beats per minute; P = 0.01). The effect was observed irrespective of the month in which observations were made, and was corroborated by more limited observations made at the beginning of the experiment. Finally, those few monkeys which rose or fell in rank were characterized by inverse changes in HR, supporting the hypothesis that behavioral factors influence HR (rather than visa versa). [ABSTRACT FROM AUTHOR]

Captive studies can make a unique contribution to primate socioecology by documenting species-typical social dispositions under controlled conditions. Recent theories seek to connect the dominance relationships, group cohesiveness, and feeding ecology of primates. The present study explores the first to aspects by comparing the social organization of rhesus (Macaca mulatta) and stumptail monkeys (M. arctoides). Data were collected over a period of eight years, with five different methods, on three well-established captive groups in identical environments. The groups were found to share one characteristic: a clear-cut, linear formal dominance hierarchy as expressed in teeth-bearing displays. The two main study groups (one of each species) differed significantly, however, with respect to nine of eleven behavioral measures. In addition to a previously reported higher frequency of reconciliation in the stumptail group, this group showed 1) more frequent but less severe aggressive behavior, 2) greater symmetry of contests, 3) greater social tolerance, 4) more nonagonistic approaches, and 5) more allogrooming. The differences can be summarized as a contrast in dominance "style," with the stumptails having a more relaxed style and placing greater emphasis on social cohesion than the rhesus monkeys. An egalitarian attitude was also reflected in approach behavior: contacts in the rhesus group were initiated dominants, whereas contacts in the stumptail group were initiated independent of rank. Comparisons with a second rhesus group, and with published reports, suggest that while some of the observed differences are probably representative of the two species, considerably intraspecific variation does exist, and a more comprehensive program of comparative studies is needed. [ABSTRACT FROM AUTHOR]

Consistent individual differences in long-term dominance care a basic underlying assumption of hypotheses linking dominance and reproductive success. Long-term and temporary dominance of a colony group of stumptailed macaques was studied for 20 years. There were two variously constituted groups for the first 4 years and a single group for the last 16. Stumptails displayed the matrilineal dominance organization found for several other cercopithecine species. A method was devised to standardize ranks so they could be compared over the years across groups of varying size and composition. No animal maintained the same dominance rank over the entire period of the research or over the last 16 years, but there was considerable consistency over long periods. Although occupants of the male and female alpha positions changed several times, one female was dominant for 18 of the 20 years. She was dominant in 1968, at the start of the study, and at its end in 1988 at which time her 18-year-old son was the dominant male. Variation in dominance ranks was greatest among members of mid-ranking matrilines and least for the lowest ranking. The same female or her son were the lowest ranking animals of their groups in all samples taken over the entire 20 years. [ABSTRACT FROM AUTHOR]

We have studied the relationship between dominance rank and physiology among male olive baboons (Papio anubis) living freely in a national park in Africa. In stable hierarchies, dominant males consistently have lower basal concentrations than do subordinates of the adrenal glucocorticoid cortisol. Because of the known catabolic actions of glucocorticoids, dominant males may be less at risk for some of the pathogenic consequences of glucocorticoid overexposure. We find that low basal cortisol concentration is not, in fact, a marker of social dominance; instead, it is only found among dominant males with a certain style of dominance. Lower basal cortisol concentrations occurred among males with any of the following behaviors: the most marked ability to distinguish between threatening and merely neutral interactions with rivals and, if the former, the greatest likelihood of initiating a fight; the most skill at distinguishing between winning and losing a fight and, if the latter, the greatest likelihood of displacing aggression onto a third party. Collectively, these behaviors suggest high degrees of social skillfulness, control, and predictability over social contingencies, all recognized as psychological features that minimize the pathophysiological impact of stress. Dominant males lacking these behavioral features, in contrast, had as high cortisol concentrations as did subordinate males. Finally, low basal cortisol concentrations were also a feature of males with the longest tenures in the dominant cohort, suggesting that this endocrine dichotomy is meaningful in terms of life histories. [ABSTRACT FROM AUTHOR]

The responses of two social groups of Cebus apella to novel or familiar objects were examined, both in scarce and in abundant conditions. The aim was to obtain a description of capuchins' general norms of behavior toward objects, focusing on the variability across sex/age classes. Plain wooden blocks were presented to each group of monkeys in four phases. In phase I, the blocks were scarce and novel; in the following phases the blocks were abundant and increasingly more familiar. Several categories of behaviors directed toward the blocks were scored. The blocks elicited high levels of responsiveness throughout the experiment. In both sexes, responsiveness tended to decrease across phases. In all phases, males interacted with the blocks more than did females. Age\was a significant determinant of responsiveness. Furthermore, age-classes showed different trends in level of responsiveness across phases. Sex and age significantly affected the behavioral pattern of interaction with the blocks. Dominance did not seem to constrain monkeys' responsiveness. The high and sustained responsiveness toward objects by Cebus apella is consistent with their manipulative skills and their varied habitat exploitation. [ABSTRACT FROM AUTHOR]

Many nonhuman primates live in complex social groups in which they regularly encounter both social stressors such as aggression and social support such as that provided by long‐term affiliative relationships. Repeated exposure to social stressors may result in chronically elevated cortisol levels that can have deleterious physical effects such as impaired immune function, cardiovascular disease, and reduced brain function. In contrast, affiliative social relationships may act as a buffer, dampening the release of cortisol in response to acute and chronic stressors. Understanding how social stressors and social support predict cortisol levels is therefore essential to understanding how social situations relate to health and welfare. We studied this relationship in 16 socially housed captive brown capuchin monkeys (Cebus [Sapajus] apella) by comparing long‐term hair cortisol levels with behavioral measures of social stress (dominance rank, rank certainty, and amount of aggression received) and social support (amount of affiliation and centrality in the affiliative social network of the group). Dominance rank, rank certainty, amount of affiliation, and age were not significant predictors of long‐term cortisol levels in this population. Instead, long‐term cortisol levels were positively related to the amount of aggression received and negatively related to centrality in the affiliative social network of the group. This pattern may be attributed to the species' socially tolerant dominance system and to the availability of social support across the dominance hierarchy. HIGHLIGHTS: Long‐term cortisol levels are positively related to the aggression received and negatively related to the centrality in the affiliative social network.Both social stressors and social support contribute to long‐term cortisol levels in primates. [ABSTRACT FROM AUTHOR]