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ABSTRACT In ecological contexts natural selection might favor individuals with a larger body mass to monopolize resources; however, there is wide variation in body mass within populations and potential factors. In this study, we evaluated whether fruit production limits body mass in one group of Sapajus apella, its effects on behavior, and whether there is a relationship between social status and body mass. We recorded activity patterns using focal follows (20 min), body mass (using a modified Ohaus scale), and community wide fruit production estimates (from 60 fruit traps). Body mass remained relatively stable during periods of food scarcity, but in periods of abundance most individuals gained weight, as indicated by their relative growth rates (RGR). Subordinate subadults showed the highest RGR, as expected by their age. In periods of high fruit production activities as traveling, grooming, and playing were more frequent than during fruit scarcity, suggesting energy maximization and potential energetic constraints. We found differences in behavior within the group, as the alpha male was observed feeding more frequently (and for longer periods of time), was more aggressive (e.g., feeding trees), and received more grooming than other individuals. In addition, the alpha male was 60% heavier than the group's average body mass. Our study supports the hypothesis that body weight gain is related to fruit abundance and that body size is associated with social dominance; however, large individuals (both males and females) seem to incur in high metabolic or reproductive costs, as they do not gain much weight as smaller individuals. [ABSTRACT FROM AUTHOR]

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]

Female dominance over males is more frequent in Malagasy lemurs than in other primate clades, but patterns of female-male dominance vary among species, and few data are available for one particularly species-rich genus, Lepilemur. We investigated the types, temporal distribution, and outcome of female-male agonistic conflicts in the Milne-Edwards' sportive lemur (Lepilemur edwardsi). Ten L. edwardsi belonging to five social units were equipped with radio collars and observed during 79 focal follows between May and November 1998. We quantified agonistic conflicts, monthly conflict rates, and documented the winner and context for all conflicts. Female-male agonistic conflicts (N = 162) occurred at a mean rate of 0.21 conflicts/hour within groups. Agonistic conflicts peaked during the birth season and occurred mostly in unknown or infant proximity contexts. Females won 96% of all decided agonistic conflicts (N = 154). Other outcomes occurred only when females were with infants during the birth season. In that context, one female sometimes withdrew from her pair partner, and another female withdrew or fled from an extra-group male whose attacks eventually led to infanticide. Our results suggest female dominance in pair-living L. edwardsi. We hypothesize that elevated female aggression may convey fitness benefits to female Lepilemur because it generally allows females to intervene quickly and efficiently on behalf of their infants against nonfather males who may approach the newborn infants when they are parked in vegetation., (© 2024 The Author(s). American Journal of Primatology published by Wiley Periodicals LLC.)

Enhanced survival and reproduction are associated with an individual's direct and indirect social connections with members of a group. Yet, the role of these connections is little known in a vast range of primate species. We studied female Central Himalayan Langur (CHL) to investigate the link between four specific attributes (dominance rank, age, genetic relatedness, and the presence of females carrying infants) and a female's direct and indirect social relationships. By analyzing grooming networks, we revealed different behavioral strategies: high-ranking females form relationships with many females (high degree), whereas females with dependent infants have strong relationships (high strength and eigenvector). Subadult females are important individuals that hold the social network together (high betweenness), while an immigrant female strategy is to integrate herself into the group by forming strong bonds with females who themselves have strong bonds (high eigenvector). Our study sheds light on how behavioral strategies shape female CHL grooming networks, which may help them to secure fitness and survival advantages., (© 2024 Wiley Periodicals LLC.)

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]

Performance in cognitive tasks has been linked to differences in species' social organization, yet to understand its function its relationship to within-species variation in behavior should also be explored. One important cognitive capacity, the ability to inhibit impulses, is typically better in egalitarian than despotic primate species and in primate species with strong fission-fusion dynamics. A different line of research indicates that a high ability to inhibit impulses is related to less aggressive behavior and more socio-positive behavior. However, within species the relationship between performance on cognitive inhibition tasks and variation in social behavior remains to be explored. Here we investigate how performance in a typical inhibition task in cognitive research is related to aggressive and socio-positive behavior in despotic long-tailed macaques. Twenty individuals living in two naturalistic mixed-sex groups were tested with the Plexiglass Hole Task. Aggressive behavior and three types of socio-positive behavior (neutral/friendly approaches, socio-positive signaling, and grooming others) among group members were measured. Individuals differed in their ability to inhibit impulses. Individuals that were not good at inhibiting impulses showed higher rates of aggressive behavior, but also more socio-positive signals, whereas inhibition was not related to neutral/friendly approaches and grooming. These results confirm the positive link between impulsiveness and aggression. In addition, the results indicate that some social-positive behavior may be enhanced when inhibition is limited. In this species, benefits potentially derived from aggression and socio-positive signals match a low ability to inhibit impulses, suggesting that a low ability to inhibit impulses may actually be advantageous. To understand differences between species in cognitive skills, understanding the benefits of variation in a cognitive capacity within a species is crucial., (© 2023 The Authors. American Journal of Primatology published by Wiley Periodicals LLC.)

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]

Though lion-tailed macaques are managed ex situ as an assurance population, little information is available on the relationship between behavior and reproductive physiology to ensure successful management and evaluate welfare. To facilitate social and reproductive management in a group of one male and three female lion-tailed macaques at Disney's Animal Kingdom®, we observed behaviors associated with dominance and reproduction, rated genital swellings, recorded menses, tracked ovarian cycles as determined by measurement of fecal immunoreactive progesterone (P4) and estradiol (E2), and monitored fecal cortisol (CORT). We analyzed the dominance hierarchy of females, compared hormone patterns of ovarian cycles with genital swellings and copulations relative to menses, and tested for correlations between hormones and behavior. The strength of the dominance hierarchy indicated moderate linearity, but relaxed after the dominant female received anxiolytic medications to reduce intraspecific aggression. Fecal P4 and E2 patterns revealed ovarian cycle lengths averaging 29.7 ± 0.8 days. The timing of single-day E2 peaks varied between and within females' cycles. However, on average, E2 peaks occurred 6-10 days after the first day of menses, with maximum genital swellings and copulations occurring slightly thereafter in uncontracepted females. Female-to-female aggression and sexual behaviors with the male were related to ovarian cycle phase, but correlations between behaviors and hormones varied between females. Initiated aggression was positively correlated with E2 in the dominant and mid-ranked females, while aggression received was positively correlated with P4 or negatively correlated with E2 in the mid-ranked and subordinate females. In one uncontracepted female, sexual behaviors with the male were negatively correlated to P4. CORT was positively correlated to aggression in the dominant and mid-ranked females and negatively correlated to grooming in the subordinate female. Results indicate observations of visual and behavioral cues can be used to track ovarian cycles and evaluate social dynamics and welfare in zoo-housed lion-tailed macaques., (© 2022 Wiley Periodicals LLC.)

The self-initiated split of a social group, known as fission, is a challenge faced by many group-living animals. The study of group fission and the social restructuring process in real time provides insights into the mechanism of this biologically important process. Previous studies on fission in Japanese macaques (Macaca fuscata) assigned individuals to newly reorganized groups mainly using behavioral observations and group attendance records based on periods before or after fission itself. Here, we present a novel framework for group classification during the process of fission that uses quantifiable behavioral variables and statistical analyses. The framework was tested on a group fission process at Affenberg Landskron (Austria), a park that housed around 160 semi-free-ranging Japanese macaques. The behavioral data were collected for 26 days during fission. We analyzed three behavioral developments recurrent in fissions in Japanese macaques, that is, independence of behavior, participation in group movements, and separation of nomadic ranges. These analyses were combined to assign individuals to different groups. Our study resulted in one main group (N = 33), one subgroup (N = 36) and 56 individuals whose group membership was still undefined. The demographic characteristics of these newly formed groups were comparable with those of fissioned groups in wild populations. Furthermore, we found that these newly forming groups showed early social dynamics of fission five months before group level movements, that is: grouping based on spatial proximity and spatial withdrawal of the subgroup to the periphery. These results underline the validity of our novel framework to study social dynamics in Japanese macaques during the process of fission. It represents an important addition to existing methods, and we recommend testing its scope in other primate societies., (© 2023 The Authors. American Journal of Primatology published by Wiley Periodicals LLC.)

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]

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]

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]

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]

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]

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]

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]

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]

The assumed evolutionary advantage of dominance is increased reproductive success. However, the efficacy of dominance as a mating strategy may be interrupted by any number of variables including female choice, estrous synchrony, and mating by non-troop males. In Japanese macaques (Macaca fuscata), there is evidence both for and against dominance as conferring reproductive success for adult males, with many discussions pointing to the importance of female choice in governing reproductive success in certain populations. In this study, we aimed to evaluate dominance-based versus female choice-based male behavioral strategies and their impact on reproductive success. This study was conducted on a group of Japanese macaques at the Oregon National Primate Research Center. We collected a total of 512 h of behavioral data across two summer study periods in 2018 and 2019. We conducted 15-min focal follows with 1-min instantaneous scans on 17 adult males. Reproductive data were available from genetic records. Using principal components analysis (PCA), we identified males that cluster according to similar behavioral strategies. We then used analysis of variance (ANOVA) and non-parametric ANOVA on ranks to ascertain significant variation in rank and reproductive success between clusters. We found that males that clustered based on high directed aggression held higher rank than less-aggressive male clusters (F = 27.21, df = 4, p < .0001). However, less aggressive male clusters had higher reproductive success (F = 3.50, df = 4, p = .04). There was no variation between affiliative clusters in reproductive success (F = 1.77, df = 3, p = .15). The highly aggressive strategy is effective for attaining high rank, but only resulted in high reproductive success for a single male which likely necessitates alternative strategies. We suggest the operation of female choice within this population, with females preferentially mating with males who are not only affiliative but also less aggressive., (© 2021 Wiley Periodicals LLC.)

Androgens are important mediators of male-male competition in many primate species. Male gorillas' morphology is consistent with a reproductive strategy that relies heavily on androgen-dependent traits (e.g., extreme size and muscle mass). Despite possessing characteristics typical of species with an exclusively single-male group structure, multimale groups with strong dominance hierarchies are common in mountain gorillas. Theory predicts that androgens should mediate their dominance hierarchies, and potentially vary with the type of group males live in. We validated the use of a testosterone enzyme immunoassay (T-EIA R156/7, CJ Munro, UC-Davis) for use with mountain gorilla fecal material by (1) examining individual-level androgen responses to competitive events, and (2) isolating assay-specific hormone metabolites via high-performance liquid chromatography. Males had large (2.6- and 6.5-fold), temporary increases in fecal androgen metabolite (FAM) after competitive events, and most captured metabolites were testosterone or 5α-dihydrotestosterone-like androgens. We then examined the relationship between males' dominance ranks, group type, and FAM concentrations. Males in single-male groups had higher FAM concentrations than males in multimale groups, and a small pool of samples from solitary males suggested they may have lower FAM than group-living peers. However, data from two different time periods (n = 1610 samples) indicated there was no clear relationship between rank and FAM concentrations, confirming results from the larger of two prior studies that measured urinary androgens. These findings highlight the need for additional research to clarify the surprising lack of a dominance hierarchy/androgen relationship in mountain gorillas., (© 2021 Wiley Periodicals LLC.)

Social network analysis is increasingly common in studying complex interactions among individuals. Across a range of primates, high-ranking adults are generally more socially connected, which results in better fitness outcomes. However, it still remains unclear whether this relationship between social network position and dominance rank emerges in infancy and whether, in species with a social transmission of dominance rank, social network positions are driven by the presence of the mother. To fill this gap, we first explored whether dominance ranks were related to social network position, measured via eigenvector centrality, in infants, juveniles, and adults in a troop of semi-free-ranging rhesus macaques (Macaca mulatta). We then examined relationships between dominance rank and eigenvector centrality in a peer-only group of yearlings who were reared with their mothers in either a rich, socially complex environment of multigenerational (MG) kin support or a unigenerational group of mothers and their infants from birth through 8 months. In Experiment 1, we found that mother's network position predicted offspring network position and that dominants across all age categories were more central in affiliative networks (social contact, social grooming, and social play). Experiment 2 showed that high-ranking yearlings in a peer-only group were more central only in the social contact network. Moreover, yearlings reared in a socially complex environment of MG kin support were more central. Our findings suggest that the relationship between dominance rank and social network position begins early in life, and that complex early social environments can promote later social competency. Our data add to the growing body of evidence that the presence/absence of the mother and kin influence how dominance rank affects social network position. These findings have important implications for the role of caregivers in the social status of developing primates, which ultimately ties to health and fitness outcomes., (© 2019 Wiley Periodicals, Inc.)

Anogenital distance (AGD) is positively correlated to fetal androgen exposure and developmental masculinization in mammals. Independent of overall body size, AGD shows a strong positive correlation with male fertility and in rodents, AGD is a good indicator of male competitive ability and is associated with female choice. We hypothesized that AGD will also predict male competitive ability in non-human primates. To test this, we measured AGD noninvasively with a parallel laser in a wild population of Angolan colobus monkeys (Colobus angolensis ruwenzorii) in Uganda and correlated to it to their social structure. C. angolensis ruwenzorii form a multilevel society with both one-male/multifemale units (OMUs) and multimale/multifemale units (MMUs). We compared AGD in males from five OMUs and six MMUs and related it to their fecal androgen metabolite concentrations, dominance rank and body size, and to the number of females in their unit. Males in OMUs had greater access to females, so were predicted to have longer AGDs, but this was not found. AGD also did not correlate overall with mean fecal androgen metabolites in MMUs. However, AGD was correlated with dominance rank in MMUs, demonstrating that higher-ranking males in these multimale units had longer AGDs. Body size did not show the same relationship with dominance rank, suggesting that male rank was not just a reflection of absolute male size. Our findings indicate that AGD predicts male competitive ability in this species and that it may be a useful correlate throughout the non-human primates. These results also support the idea that prenatal androgen exposure increases the likelihood of the expression of behaviors that maintain high dominance rank., (© 2020 Wiley Periodicals, Inc.)

Social status impacts stress in primates, but the direction of the effect differs depending on species, social style, and group stability. This complicates our ability to identify broadly applicable principles for understanding how social status impacts health and fitness. One reason for this is the fact that social status is often measured as linear dominance rank, yet social status is more complex than simply high or low rank. Additionally, most research on social status and health ignores the effects of sex and sex-specific relationships, despite known differences in disease risk, coping strategies, and opposite-sex dominance interactions between males and females in many species. We examine the influence of social status, sex, and opposite-sex interactions on hair cortisol concentrations (HCC) in a well-studied species, rhesus macaques, where the literature predicts low ranking individuals would experience more chronic stress. Animals in three captive, seminaturalistic social groups (N = 252; 71 male) were observed for 6 weeks to obtain metrics of social status (rank and dominance certainty [DC]). DC is a measure of one's fit within the hierarchy. Hair samples were collected from each subject and analyzed for HCC. Generalized linear mixed models were used to examine (a) whether rank, DC, or sex predicted HCC; (b) whether same- or opposite-sex dominance relationships differentially impacted HCC; and (c) whether aggressive interactions initiated or received could explain any observed relationships. Results indicated that DC, not rank, predicted HCC in a sex-specific manner. For males, high HCC were predicted by receiving aggression from or having high DC with other males as well as having low DC with females. For females, only high DC with males predicted high HCC. These results likely relate to sex-specific life history pattern differences in inherited versus earned rank that are tied to female philopatry and male immigration., (© 2019 Wiley Periodicals, Inc.)

Access to food is of major importance to the fitness and survival of every individual, particularly in group-living animals, in which individual characteristics and food distribution can affect food intake. Additionally, several species of primates are known to share food under certain conditions. Such unresisted transfer of food from one individual to another appears to be adaptive, for instance as a tool to maintain and reinforce social bonds. In this study, we aimed to test how food retrieval and food sharing varies depending on the social relationship between individuals, and on the characteristics of the food. In six different test conditions, we provided a captive group of Guinea baboons (Papio papio, N = 23) with multiple food items, differing in quality, quantity, density, monopolizability, and effort required to obtain it. We further used behavioral observations to assess individual relationships and possible variations in grooming exchanges linked to food sharing events. Out of 424 events in which food items were retrieved by the subjects, we detected no instances of active food sharing and only 17 of passive food sharing. The way food was retrieved was affected by individual and food characteristics (i.e., quantity, quality, and monopolizability of food): Males and central individuals (i.e., those connected to many partners, and/or having partners with many connections in the social network) were more likely to retrieve food during test conditions. In particular, events of passive food sharing mostly happened when the quality of food was low, and between individuals belonging to the same community (i.e., having close relationships). No other food characteristics affected the probability to share food, and the occurrence of food sharing had no immediate effect on grooming exchanges. Overall, our findings suggest that food sharing is relatively rare in Guinea baboons unless the food has a low quality and individuals form close social bonds., (© 2019 Wiley Periodicals, Inc.)

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]

Estrogen depletion leads to bone loss in almost all mammals with frequent regular ovarian cycles. However, subordinate adult female common marmosets (Callithrix jacchus) undergo socially induced anovulation and hypoestrogenism without clinically apparent adverse skeletal consequences. Thus, we speculated that this non human primate might have evolved a mechanism to avoid estrogen-depletion bone loss. To test this possibility, we performed three experiments in which lumbar-spine (L5-L6) bone mineral content (BMC) and density (BMD) were assessed using dual-energy X-ray absorptiometry: (i) cross-sectionally in 13 long-term ovariectomized animals and 12 age- and weight-matched controls undergoing ovulatory cycles; (ii) longitudinally in 12 animals prior to, 3-4 and 6-7 months following ovariectomy (ovx), and six controls; and (iii) cross-sectionally in nine anovulatory subordinate and nine dominant females. In Experiments 1 and 3, plasma estradiol and estrone concentrations were measured and uterine dimensions were obtained by ultrasound in a subset of animals as a marker of functional estrogen depletion. Estrogen levels, uterine trans-fundus width, and uterine dorso-ventral diameter were lower in ovariectomized and subordinate females than in those undergoing ovulatory cycles. However, no differences were found in L5-L6 BMC or BMD. These results indicate that estrogen depletion, whether surgically or socially induced, is not associated with lower bone mass in female common marmosets. Thus, this species may possess unique adaptations to avoid bone loss associated with estrogen depletion., (© 2018 Wiley Periodicals, Inc.)

Male-female social interactions may vary according to female receptivity, female parity, and male dominance rank. Such variation may be less apparent in species with one-male mating systems than those with multimale mating systems, as within-group male-male competition and female mate choice are absent. Examining variation in male-female interactions in multimale groups in species with a predominantly one-male mating system may help to shed light on plasticity in behavioral patterns and the evolution of mating systems. In this study, we investigated the effect of female receptivity (i.e., days when mating occurred), female parity, and male dominance rank on the patterns of spatial proximity, grooming, following, and aggression among 34 male-female dyads in four multi-male groups of Virunga mountain gorillas. In addition, as a preliminary investigation of potential physiological costs incurred by females in a mating context (coercion), we tested whether female receptivity and female parity explained variation in immunoreactive glucocorticoid (iGC) levels of females. The amount of time male-female dyads spent in close proximity was significantly higher for parous versus nulliparous females and for high- versus low-ranking males. The rate of male aggression to females did not vary significantly with female parity, male rank, or female receptivity. However, post hoc analysis showed that both proximity and aggression increased for the males that participated in the matings on days that females were receptive. Grooming and following by males occurred infrequently. Neither female receptivity nor parity influenced iGC levels in females, a finding that is more consistent with courtship than coercion of females by males. Overall, our results suggest that males advertise their ability to provide protection to females and their offspring, and females seek out males that can do so., (© 2018 Wiley Periodicals, Inc.)

In the present study, we compared mother-infant relationships in 57 mother-infant dyads residing in two wild, semi-provisioned (22 mother-infant dyads in 2014, 35 dyads in 2015) groups of rhesus macaques (Macaca mulatta) in the Nanwan Nature Reserve for Rhesus Macaques, Hainan, China. We also compared reproductive success between these two groups. The ecology and provisioning regime for each group was similar. These groups differed however, in size. Group 1 contained ∼35 individuals and Group 2 contained ∼120 individuals. Data were collected over a 2-year period (2014-2015). We found that during the birth season, mother-infant relationships in the larger group were characterized by less time in contact and more time separated than in the smaller group. Mothers in the smaller group initiated more contact and proximity with their infants. During the mating season when infants were approximately 6 months old, mother-infant relationships in the smaller group were more rejecting. We also found that birth rates were significantly higher but infant survivorship (to 1-year-old) was significantly lower in the smaller group. Moreover, higher-ranking mothers in the larger group were characterized by a higher reproductive output than females of lower rank. In the smaller group, female rank did not affect reproductive output. There was, however, no clear relationship between infant survivorship and maternal rank. We hypothesize that differences in reproductive success and changes in mother-infant relationships between the birth and mating seasons reflect differences in the costs and benefits of group size: females in the larger group faced (i) higher intragroup feeding competition leading to a reduction in birth rate but also (ii) lower predation risk, resulting in higher infant survival rate compared to females in the smaller group. The results of this study point to the tradeoffs that primate females face in living in smaller and larger social groups., (© 2018 Wiley Periodicals, Inc.)

The critically endangered Claire's mouse lemur, only found in the evergreen rain forest of the National Park Lokobe (LNP) and a few lowland evergreen rain forest fragments of northern Madagascar, was described recently. The present study provides the first quantified information on vocal acoustics of calls, sound associated behavioral context, acoustic niche, and vocal activity of this species. We recorded vocal and social behavior of six male-female and six male-male dyads in a standardized social-encounter paradigm in June and July 2016 at the LNP, Nosy Bé island. Over six successive nights per dyad, we audio recorded and observed behaviors for 3 hr at the beginning of the activity period. Based on the visual inspection of spectrograms and standardized multiparametric sound analysis, we identified seven different call types. Call types can be discriminated based on a combination of harmonicity, fundamental frequency variation, call duration, and degree of tonality. Acoustic features of tonal call types showed that for communication, mouse lemurs use the cryptic, high frequency/ultrasonic frequency niche. Two call types, the Tsak and the Grunt call, were emitted most frequently. Significant differences in vocal activity of the Tsak call were found between male-female and male-male dyads, linked primarily to agonistic conflicts. Dominant mouse lemurs vocalized more than subdominant ones, suggesting that signaling may present an honest indicator of fitness. A comparison of our findings of the Claire's mouse lemur with published findings of five bioacoustically studied mouse lemur species points to the notion that a complex interplay between ecology, predation pressure, and phylogenetic relatedness may shape the evolution of acoustic divergence between species in this smallest-bodied primate radiation. Thus, comparative bioacoustic studies, using standardized procedures, are promising to unravel the role of vocalization for primate species diversity and evolution and for identifying candidates for vocalization-based non-invasive monitoring for conservation purposes., (© 2018 Wiley Periodicals, Inc.)

The social relationships that individuals experience at different life stages have a non-negligible influence on their lives, and this is particularly true for group living animals. The long lifespan of many primates makes it likely that these animals have various tactics of social interaction to adapt to complex changes in environmental or physical conditions. The different strategies used in social interaction by individuals at different life stages, and whether the position (central or peripheral) or role (initiator or recipient) of an individual in the group social network changes with age, are intriguing questions that remain to be investigated. We used social network analysis to examine age-related differences in social interaction patterns, social roles, and social positions in three affiliative social networks (approach, allogrooming, and social play) in a group of wild rhesus macaques (Macaca mulatta). Our results showed that social interaction patterns of rhesus macaques differ between age classes in the following ways: i) young individuals tend to allocate social time to a high number of groupmates, older individuals prefer to focus on fewer, specific partners; ii) as they grow older, individuals tend to be recipients in approach interactions and initiators in grooming interactions; and iii) regardless of the different social interaction strategies, individuals of all ages occupy a central position in the group. These results reveal a possible key role played by immature individuals in group social communication, a little-explored issue which deserves closer investigation in future research., (© 2017 Wiley Periodicals, Inc.)

Previous studies of nonhuman primates have found relationships between health and individual differences in personality, behavior, and social status. However, despite knowing these factors are intercorrelated, many studies focus only on a single measure, for example, rank. Consequently, it is difficult to determine the degree to which these individual differences are independently associated with health. The present study sought to untangle the associations between health and these individual differences in rhesus macaques (Macaca mulatta). We studied 85 socially housed macaques at the Oregon and California National Primate Research Centers, and used veterinary records to determine the number of injuries and illnesses for each macaque. We measured personality using 12 items from a well-established primate personality questionnaire, performed focal observations of behaviors, and calculated dominance status from directional supplant data. All twelve personality questionnaire items were reliable and were used to represent five of the six personality dimensions identified in rhesus macaques-Dominance, Confidence, Openness, Anxiety, and Friendliness (also known as Sociability). Following this, we fit generalized linear mixed effects models to understand how these factors were associated with an animal's history of injury and history of illness. In the models, age was an offset, facility was a random effect, and the five personality dimensions, behavior, sex, and dominance status were fixed effects. Number of injuries and illnesses were each best represented by a negative binomial distribution. For the injury models, including the effects did improve model fit. This model revealed that more confident and more anxious macaques experienced fewer injuries. For the illness models, including the fixed effects did not significantly improve model fit over a model without the fixed effects. Future studies may seek to assess mechanisms underlying these associations., (© 2018 Wiley Periodicals, Inc.)

Among nonhuman primates, the evolutionary underpinnings of variation in social structure remain debated, with both ancestral relationships and adaptation to current conditions hypothesized to play determining roles. Here we assess whether interspecific variation in higher-order aspects of female macaque (genus: Macaca) dominance and grooming social structure show phylogenetic signals, that is, greater similarity among more closely-related species. We use a social network approach to describe higher-order characteristics of social structure, based on both direct interactions and secondary pathways that connect group members. We also ask whether network traits covary with each other, with species-typical social style grades, and/or with sociodemographic characteristics, specifically group size, sex-ratio, and current living condition (captive vs. free-living). We assembled 34-38 datasets of female-female dyadic aggression and allogrooming among captive and free-living macaques representing 10 species. We calculated dominance (transitivity, certainty), and grooming (centrality coefficient, Newman's modularity, clustering coefficient) network traits as aspects of social structure. Computations of K statistics and randomization tests on multiple phylogenies revealed moderate-strong phylogenetic signals in dominance traits, but moderate-weak signals in grooming traits. GLMMs showed that grooming traits did not covary with dominance traits and/or social style grade. Rather, modularity and clustering coefficient, but not centrality coefficient, were strongly predicted by group size and current living condition. Specifically, larger groups showed more modular networks with sparsely-connected clusters than smaller groups. Further, this effect was independent of variation in living condition, and/or sampling effort. In summary, our results reveal that female dominance networks were more phylogenetically conserved across macaque species than grooming networks, which were more labile to sociodemographic factors. Such findings narrow down the processes that influence interspecific variation in two core aspects of macaque social structure. Future directions should include using phylogeographic approaches, and addressing challenges in examining the effects of socioecological factors on primate social structure., (© 2017 Wiley Periodicals, Inc.)

Early life experiences are known to influence hypothalamic-pituitary-adrenal (HPA) axis development, which can impact health outcomes through the individual's ability to mount appropriate physiological reactions to stressors. In primates, these early experiences are most often mediated through the mother and can include the physiological environment experienced during gestation. Here, we investigate stress physiology of dependent offspring in wild chimpanzees for the first time and examine whether differences in maternal stress physiology are related to differences in offspring stress physiology. Specifically, we explore the relationship between maternal rank and maternal fecal glucocorticoid metabolite (FGM) concentration during pregnancy and early lactation (first 6 months post-partum) and examine whether differences based on maternal rank are associated with dependent offspring FGM concentrations. We found that low-ranking females exhibited significantly higher FGM concentrations during pregnancy than during the first 6 months of lactation. Furthermore, during pregnancy, low-ranking females experienced significantly higher FGM concentrations than high-ranking females. As for dependent offspring, we found that male offspring of low-ranking mothers experienced stronger decreases in FGM concentrations as they aged compared to males with high-ranking mothers or their dependent female counterparts. Together, these results suggest that maternal rank and FGM concentrations experienced during gestation are related to offspring stress physiology and that this relationship is particularly pronounced in males compared to females. Importantly, this study provides the first evidence for maternal effects on the development of offspring HPA function in wild chimpanzees, which likely relates to subsequent health and fitness outcomes. Am. J. Primatol. 80:e22525, 2018. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Disease and other health hazards pose serious threats to the persistence of wild ape populations. The total chimpanzee population at Gombe National Park, Tanzania, has declined from an estimated 120 to 150 individuals in the 1960's to around 100 individuals by the end of 2013, with death associated with observable signs of disease as the leading cause of mortality. In 2004, we began a non-invasive health-monitoring program in the two habituated communities in the park (Kasekela and Mitumba) with the aim of understanding the prevalence of health issues in the population, and identifying the presence and impacts of various pathogens. Here we present prospectively collected data on clinical signs (observable changes in health) in the chimpanzees of the Kasekela (n = 81) and Mitumba (n = 32) communities over an 8-year period (2005-2012). First, we take a population approach and analyze prevalence of clinical signs in five different categories: gastrointestinal system (diarrhea), body condition (estimated weight loss), respiratory system (coughing, sneezing etc.), wounds/lameness, and dermatologic issues by year, month, and community membership. Mean monthly prevalence of each clinical sign per community varied, but typically affected <10% of observed individuals. Secondly, we analyze the presence of clinical signs in these categories as they relate to individual demographic and social factors (age, sex, and dominance rank) and simian immunodeficiency virus (SIVcpz) infection status. Adults have higher odds of being observed with diarrhea, loss of body condition, and wounds or lameness when compared to immatures, while males have a higher probability of being observed with wounds or lameness than females. In contrast, signs of respiratory illness appear not to be related to chimpanzee-specific factors and skin abnormalities are very rare. For a subset of known-rank individuals, dominance rank predicts the probability of wounding/lameness in adult males, but does not predict any adverse clinical signs in adult females. Instead, adult females with SIVcpz infection are more likely to be observed with diarrhea, a finding that warrants further investigation. Comparable data are needed from other sites to determine whether the prevalence of clinical signs we observe are relatively high or low, as well as to more fully understand the factors influencing health of wild apes at both the population and individual level. Am. J. Primatol. 80:e22562, 2018. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Infanticide is common in the context of alpha male replacements (AMR), particularly in groups where alpha males experience high reproductive skew and the infants are unlikely to be related to a new alpha male. We examined the relationship between the rate of infant mortality, infant age, and the occurrence and type of AMR in white-faced capuchin monkeys (Cebus capucinus imitator) of the Santa Rosa population in Sector Santa Rosa, Área de Conservación Guanacaste. Specifically, we investigated how the source of the new alpha male (coresident or extragroup) and relative aggression level during AMRs influenced infant mortality in this species. Between 1986 and 2015, we recorded 221 births in five study groups. Infants present at the time of an AMR, or born within 5.5 months following an AMR (i.e., conceived prior to AMR), experienced significantly higher mortality than those born during periods of group stability. Infant age was a significant predictor of infant survival, with the probability of surviving increasing by 0.4% for each additional day older an infant was at the time of the AMR. Infant mortality rates did not differ between AMRs by coresident males and extragroup males, possibly because the degree of relatedness between infants and new alphas did not significantly differ between coresident and extragroup AMRs. Infant mortality rates did not differ significantly between aggressive AMRs and more peaceful AMRs. Our results are consistent with predictions derived from the sexual selection hypothesis (SSH) of infanticide and suggest that future studies examine the role of testosterone as an underlying proximate mechanism for the aggression leading to this behavior. We argue that the sexual selection and generalized aggression hypotheses (GAH) of infanticide are best considered as different levels of analysis rather than competing hypotheses., (© 2017 Wiley Periodicals, Inc.)

Sexual selection for honest behavioral displays of quality has driven the development of remarkably complex courtship behavior in many animal species. Olfactory displays are often overlooked as an area of inquiry compared to auditory and visual displays. Ring-tailed lemur (Lemur catta) scent marking of substrates has been studied extensively, although the male olfactory displays of anointing and wafting tails to females has received relatively little attention. We studied the role of male olfactory displays to females, evaluating whether such signals function as honest, costly signals of male dominance status in two groups of wild L. catta at Berenty Reserve, Madagascar. Our results suggest that male tail anointing and tail wafting displays to pre-estrous and estrous females are correlated with male dominance rank, and moreover appear to operate as costly signals, as such displays increase aggression received from males and females while other types of scent marking do not. Furthermore, females showed greater mating preference (as measured by sexual presents) for resident males who performed the "anoint tail" and "waft tail" displays towards them. When males perform the "anoint tail" and "waft tail" displays to females, they receive higher levels of aggression than if they were to perform other types of scent marking. Interestingly, immigrating (peripheral) males performed the "anoint tail" and "waft tail" displays at higher rates than resident males, which could honestly indicate their quality or may simply be associated with the alternative mating strategy of transferring between groups to gain mating opportunities. Our finding that tail anointing and tail wafting displays function as honest signals of dominance for resident males-and that these costly displays appear to positively affect female mate choice-is the first evidence of this function for this particular olfactory signal in L. catta., (© 2017 Wiley Periodicals, Inc.)

Growing evidence from studies on primates and other taxa has shown that the maintenance of long-term affiliative patterns influences fitness. Thus, understanding how individuals regulate social interactions in response to environmental and social factors contributes to our understanding of the evolutionary basis of sociality. We investigated the durability of affiliation patterns in chimpanzees across three 3-month periods of varying social uncertainty depending on the degree of stability in the male hierarchy, with a 2-year gap between each period. Periods were unstable (no clear alpha male), recently stable (new alpha male just established) and stable (alpha male in place for 2 years). We focused on three features of social exchange shared by human and non-human primates: consistency of exchanges across periods, durability of preferred partners, and degree of reciprocity in each period. We compared male-to-male, female-to-female, male-to-female, and female-to-male grooming patterns. Overall, more grooming was exchanged in the stable period. Grooming patterns were not consistent across the three periods, but were only consistent between the recently stable and stable periods for female-to-female and male-to-female dyads. As predicted from the opportunistic nature of male relationships, male-to-male grooming was least likely to be correlated across all periods and males had relatively fewer durable (i.e., preferred partners in all periods) same-sex partners than females. Our predictions that grooming reciprocity would be less likely during the unstable period and in male-male dyads were only partially supported. We found grooming reciprocity in all periods for female-female dyads but only in the stable period for male-male and female-male dyads. Although long-term affiliative patterns are well studied in primates, this is the first study to investigate the association between social uncertainty and durability of affiliative patterns. Our findings suggest social uncertainty influences social exchange and highlight the importance of considering group instability in studies of social relationships., (© 2017 Wiley Periodicals, Inc.)