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Objectives: In primates, allogrooming and other affiliative behaviors confer many benefits and may be influenced by many socioecological factors. Of these, the impact of anthropogenic factors remain relatively understudied. Here we ask whether interactions with humans decreased macaques' affiliative behaviors by imposing time‐constraints, or increased these behaviors on account of more free‐/available‐time due to macaques' consumption of high‐energy human foods. Materials and methods: In Southern India, we collected data on human–macaque and macaque–macaque interactions using focal‐animal sampling on two groups of semi‐urban bonnet macaques for 11 months. For each macaque within each climatic season, we calculated frequencies of human–macaque interactions, rates of monitoring human activity and foraging on anthropogenic food, dominance ranks, grooming duration, number of unique grooming partners, and frequencies of other affiliative interactions. Results: We found strong evidence for time‐constraints on grooming. Macaques that monitored humans more groomed for shorter durations and groomed fewer partners, independent of their group membership, sex, dominance rank, and season. However, monitoring humans had no impact on other affiliative interactions. We found no evidence for the free‐time hypothesis: foraging on anthropogenic food was unrelated to grooming and other affiliation. Discussion: Our results are consistent with recent findings on other urban‐dwelling species/populations. Macaques in such environments may be especially reliant on other forms of affiliation that are of short duration (e.g., coalitionary support, lip‐smacking) and unaffected by time‐constraints. We stress on the importance of evaluating human impact on inter‐individual differences in primate/wildlife behavior for conservation efforts. [ABSTRACT FROM AUTHOR]

The social group hierarchy of three captive C. petaurista specimens was monitored and determined by observing agnostic fights, aggression, and allogrooming incidents. This social group was monitored from May to August in 2017 for 60.5 observation hours total as a continuation of a previous study conducted in spring of 2017. The study took place at the Central Florida Zoo and Botanical Gardens. All observations were recorded on template sheets with the location of each individual noted on a 6x6 grid representing the enclosure. A new sheet was used for each 15-minute increment during observation periods. It was concluded that agnostic fight outcomes were influenced by social hierarchy, with more dominant individuals consistently winning encounters with less dominant individuals. It was also notable how the dominant male would step in to help settle agnostic fights, enforcing the hierarchy among less dominant individuals. Allogrooming also was influenced by hierarchy. Grooming incidents among the observed specimens followed the Seyfarth model, meaning that grooming tended to take place among individuals of adjacent rank. [ABSTRACT FROM AUTHOR]

Allogrooming is a key aspect of chimpanzee sociality and many studies have investigated the role of reciprocity in a biological market. One theoretical form of reciprocity is time-matching, where payback consists of an equal duration of effort (e.g. twenty seconds of grooming repaid with twenty seconds of grooming). Here, we report a study of allogrooming in a group of twenty-six captive chimpanzees (Chester Zoo, UK), based on more than 150 hours of data. For analysis, we introduce a methodological innovation called the “Delta scale”, which unidimensionally measures the accuracy of time-matching according to the extent of delay after the cessation of grooming. Delta is positive when reciprocation occurs after any non-zero delay (e.g. A grooms B and then B grooms A after a five second break) and it is negative when reciprocation begins whilst the original grooming has not yet ceased. Using a generalized linear mixed-method, we found evidence for time-matched reciprocation. However, this was true only for immediate reciprocation (Delta less than zero). If there was a temporal break in grooming between two members of a dyad, then there was no evidence that chimpanzees were using new bouts to retroactively correct for time-matching imbalances from previous bouts. Our results have implications for some of the cognitive constraints that differentiate real-life reciprocation from abstract theoretical models. Furthermore, we suggest that some apparent patterns of time-matched reciprocity may arise merely due to the law of large numbers, and we introduce a statistical test which takes this into account when aggregating grooming durations over a window of time. [ABSTRACT FROM AUTHOR]

Three mechanisms have been proposed to underlie reciprocation of social behaviors in gregarious animals: "calculated reciprocity," "emotional bookkeeping," and "symmetry-based reciprocity." Among these explanations, emotional book-keeping has received the broadest support from experimental and observational studies. On the other hand, 3 individual-based models have shown that reciprocation may emerge via "symmetry-based reciprocity," "emotional bookkeeping," or a combination of both mechanisms. Here, we use these 3 models to assess their relative fit with empirical data on reciprocation and social network structure across different groups and species of macaques. We collected grooming data from 14 groups and 8 macaque species and simulated each group in each model. We analyzed and quantitatively compared social network metrics of the empirical and the models' grooming networks. The 3 models captured fairly well the features of observed networks, and fitted data from wild groups better than captive ones. The emotional bookkeeping model seemed on average to fit slightly better the social networks metrics observed in empirical data, but failed to reproduce some grooming patterns. The symmetry-based models, on the other hand, fitted better other network parameters (e.g., modularity). No model generally fitted the data better than the others, and the fit with some metrics (e.g., modularity, centralization index) was low even after optimization. Thus, our analyses indicate that in the models social interactions may be simpler than in reality and models may miss social processes (e.g., third-party awareness). [ABSTRACT FROM AUTHOR]

Social play and grooming are typical affiliative interactions for many primate species, and are thought to have similar biological functions. However, grooming increases with age, whereas social play decreases. We proposed the hypothesis that both social grooming and social play in juveniles strengthen their social bonds in daily activities. We carried out field research on the social relationships among juvenile wild Japanese macaques in a troop in Kinkazan, Miyagi Prefecture, Japan, from fall 2007 to spring 2008 to investigate this hypothesis. We evaluated three relationships among juveniles, play indices (PI), grooming indices (GI), and 3‐m‐proximity indices (3mI) of each dyad (i.e., interacting pair), and compared these social networks based on the matrices of the indices. The play and grooming networks were correlated with the association network throughout the two research periods. The multiple network level measurements of the play network, but not the grooming network, resembled those of the association network. Using a causal step approach, we showed that social play and grooming interactions in fall seem to predict associations in the following spring, controlling for the PI and GI matrix in spring, respectively. Social play and grooming for each juvenile were negatively correlated. The results partially support our predictions; therefore, the hypothesis that the biological function of social play among immature Japanese macaques is to strengthen their social bonds in the near future and develop their social life appears to be correct. For juvenile macaques, social play, rather than grooming, functions as an important social mechanism to strengthen affiliative relationships. [ABSTRACT FROM AUTHOR]

Group-level cooperation often poses a social dilemma in which joint action may be difficult to achieve. Theoretical models and experimental work on humans show that social incentives, such as punishment of defectors and rewarding of cooperators, can promote cooperation in groups of unrelated individuals. Here, we demonstrate that these processes can operate in a nonhuman animal species, and be used to effectively promote the production of a public good. We took advantage of the fact that intergroup fights in vervet monkeys (Chlorocebus aethiops pygerythrus) are characterized by episodes of intergroup aggression with pauses in-between. During pauses, females selectively groomed males that had participated in the previous aggressive episode, but aggressed male group members that had not. In subsequent (i.e. future) episodes, males who had received either aggression or grooming participated above their personal base-line level. Therefore, female-male aggression and grooming both appear to function as social incentives that effectively promote male participation in intergroup fights. Importantly, females stood to gain much from recruiting males as the probability of winning intergroup fights was dependent on the number of active participants, relative to the number of fighters in the opposing group. Furthermore, females appear to maximize the benefits gained from recruiting males as they primarily used social incentives where and when high-quality food resources, which are the resources primarily limiting to female fitness, were at stake. [ABSTRACT FROM AUTHOR]

Research on leadership is a critical step for understanding collective decision making. However, only 4 of the 22 extant macaque species have been examined for the impact of social rank and affiliation on the initiation of collective movement. It is far from clear whether such impact exists and, if so, how it works among other macaques. To answer these questions, we investigated free-ranging, Tibetan macaques' ( Macaca thibetana) group departures from a provisioning area and tested two alternative hypotheses: personal versus distributed leadership. Personal leadership predicts that a single, highest ranking individual initiates the most group movements, whereas distributed leadership predicts that different members lead the group on different occasions and affiliative individuals have more initiations. We recorded how often and how successfully adults initiated group movements from a provisioning area into the forest, and related these variables to the duration of interindividual proximity and grooming time in the forest. All adults initiated group movements, but did so variably. Social rank was related neither to the number of successful initiations nor to the success ratio of initiations. By contrast, eigenvector centrality based on proximity relations was positively correlated with the number and ratio of successful initiations. Moreover, successful initiations were positively correlated with social grooming. Overall, Tibetan macaques showed a pattern of distributed leadership. Our study demonstrated the relationship between social affiliation and individual leadership in a macaque society. Am. J. Primatol. 78:816-824, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Both wild and captive studies of grooming in non-human primates emphasize the adaptive role of this behavior. Indeed, social grooming is frequently characterized as “social glue” in the life of primates. Grooming behavior is studied to reveal dominance, kin relations, and social networks. Many captive primates, including apes, are observed to over-groom which may result in denuding of individuals. This study focused on a discrete pattern of grooming, specifically hair plucking—a rapid jerking away of the hand or mouth to remove the hair and hair follicle, often accompanied by inspection and consumption of the hair and follicle. This pattern has never been reported for wild bonobos ( Pan paniscus ) but is routinely observed in many individuals in captive colonies. Subjects were 17 bonobos (4 wild-born and 13 captive-born) housed at the Columbus Zoo. Data on grooming behavior were collected using all-occurrence sampling. Approximately 21% of self-directed and dyadic grooming bouts involved hair plucking. The four wild-born individuals were never observed to hair pluck. While plucking was not significantly different between males and females, subadult males plucked significantly more than adult males. Self-directed plucking appears to be influenced by dominance—the dominant male and female showed the highest percent of self-directed plucking behavior, 54% and 57%, respectively. This is the first study to document the significance of plucking in bonobo grooming behavior and contributes to discussions of visitors’ perception of ape well being. [ABSTRACT FROM AUTHOR]

Flexibly adapting social behavior to social and environmental challenges helps to alleviate glucocorticoid (GC) levels, which may have positive fitness implications for an individual. For primates, the predominant social behavior is grooming. Giving grooming to others is particularly efficient in terms of GC mitigation. However, grooming is confined by certain limitations such as time constraints or restricted access to other group members. For instance, dominance hierarchies may impact grooming partner availability in primate societies. Consequently specific grooming patterns emerge. In despotic species focusing grooming activity on preferred social partners significantly ameliorates GC levels in females of all ranks. In this study we investigated grooming patterns and GC management in Barbary macaques, a comparably relaxed species. We monitored changes in grooming behavior and cortisol (C) for females of different ranks. Our results show that the C-amelioration associated with different grooming patterns had a gradual connection with dominance hierarchy: while higher-ranking individuals showed lowest urinary C measures when they focused their grooming on selected partners within their social network, lower-ranking individuals expressed lowest C levels when dispersing their grooming activity evenly across their social partners. We argue that the relatively relaxed social style of Barbary macaque societies allows individuals to flexibly adapt grooming patterns, which is associated with rank-specific GC management. Am. J. Primatol. 77:688-700, 2015. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In primates, grooming is considered among the most common behaviors for maintaining social bonds; however, to date, few studies have examined grooming behavior in gibbon species in detail. We used both a 5-min interval scan method and social network analysis to study grooming in two groups of polygynous western black-crested gibbon ( Nomascus concolor) in Wuliang Mountain, Central Yunnan, China. Individuals in both groups spent little time in social grooming (1.45% and 1.97% of active time). We compared the two groups' grooming networks and found that the group that maintained a more stable social unit had a more complex grooming network while the group with new immigrants had a grooming network characterized by fewer grooming pairs. Females in both groups played important roles in the grooming network. A newly immigrant female spent the most time grooming others and chose the resident adult female as her main adult grooming partner. Other females from both groups chose the adult male as their primary grooming partner (except their offspring). A sub-adult male who had resided in his natal group for 2 years after maturing into an adult also groomed more and was at the center of the network. This male finally replaced the breeding male in his group 3 years after our data collection period ended. We hypothesize that the immigrant female and the resident young adult male engaged in more extensive grooming interactions as a behavioral strategy to gain tolerance from long-term residents. Our results suggest that female gibbons in polygynous groups actively cooperate in maintaining social relationships rather than co-exist through tolerance or avoidance. Our observations indicate that grooming networks in crested gibbons reflect individual dynamics and partly support the social cohesion hypothesis for primate grooming. In this regard, we suggest that changes in gibbon grooming networks can be used to predict social change. Am. J. Primatol. 75:1165-1173, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Social grooming is an important element of social life in terrestrial primates, inducing the putative benefits of β-endorphin stimulation and group harmony and cohesion. Implicit in many analyses of grooming (e.g. biological markets) are the assumptions of costs and benefits to grooming behaviour. Here, in a review of literature, we investigate the proximate costs and benefits of grooming, as a potentially useful explanatory substrate to the well-documented ultimate (functional) explanations. We find that the hedonic benefits of grooming are well documented. However, we did not find convincing evidence for costs. If proximate costs do exist, they might consist of energetic, cognitive, opportunity costs, or some combination of all of these. Nonetheless, there remains the possibility that grooming costs are negligible, or even that the provision of allogrooming is rewarding in itself. We suggest empirical research to resolve this issue. [ABSTRACT FROM AUTHOR]

Both wild and captive chimpanzees (Pan troglodytes) share food with non-relatives. Researchers have proposed several hypotheses to explain this behavior, including 'food for sex', 'food for grooming or agonistic support', and 'sharing under pressure'. We examined food sharing in two captive groups of socially-housed chimpanzees. In contrast to previous captive studies, which only examined transfers of low-quality foods, we conducted seven trials with high-quality food and seven with low-quality food for each group to directly compare transfers of different food qualities. We recorded how male chimpanzees shared food, including active transfers, passive transfers, and co-feeding. We also noted all instances of copulations, female estrous states, benign attempts to access food (termed 'perseverance'), and aggressive attempts (termed 'harassment') to examine whether any of these factors influenced food sharing. Male food possessors shared at the same rate in both food quality conditions, but seemingly for different reasons, indicating that food quality may affect the exchange of social benefits in chimpanzees. In the low-quality condition, there was an interaction with rank and perseverance: while low- and middle-ranking females received more food the more they persevered, high-ranking females received more food without perseverance and gained relatively little benefit from persevering. In the high-quality condition, there was an interaction between copulations and perseverance: females who copulated with the male food possessor received more food during that trial with less perseverance. Non-copulating females received more transfers the more they persevered. This result was only observed in the shortterm -- copulations over the previous year were not correlated with food transfers. Further, the copulations observed here were unusual for these chimpanzees in that they were not confined to peak fertility, suggesting a non-conceptive function for copulations in chimpanzees. Copulations in this study may have functioned to reduce tension and increase short-term tolerance, allowing females better access to food. [ABSTRACT FROM AUTHOR]

Abstract: It is well established that allogrooming, which evolved for a hygienic function, has acquired an important derived social function in many primates. In particular, it has been postulated that grooming may play an essential role in group cohesion and that human language, as verbal grooming or gossip, evolved to maintain group cohesion in the hominin lineage with its unusually large group sizes. Here, we examine this group cohesion hypothesis and test it against the alternative grooming-need hypothesis which posits that rates of grooming are higher in species where grooming need (i.e. the motivation to groom for hygiene and its associated psychological reward) is more pronounced. This alternative predicts that the derived social function of grooming evolved mostly in those lineages that had the highest exposure to ectoparasites and dirt, i.e. terrestrial species. A detailed comparative analysis of 74 species of wild primates, controlling for phylogenetic non-independence, showed that terrestriality was a highly significant predictor of allogrooming time, consistent with the prediction. The predictions of the group cohesion hypothesis were not supported, however. Group size did not predict grooming time across primates, nor did it do so in separate intra-population analyses in 17 species. Thus, there is no comparative support for the group-cohesion function of allogrooming, which questions the role of grooming in the evolution of human language. [Copyright &y& Elsevier]

Grooming handclasp (GHC) behaviour was originally advocated as the first evidence of social culture in chimpanzees owing to the finding that some populations engaged in the behaviour and others do not. To date, however, the validity of this claim and the extent to which this social behaviour varies between groups is unclear. Here, we measured (i) variation, (ii) durability and (iii) expansion of the GHC behaviour in four chimpanzee communities that do not systematically differ in their genetic backgrounds and live in similar ecological environments. Ninety chimpanzees were studied for a total of 1029 h; 1394 GHC bouts were observed between 2010 and 2012. Critically, GHC style (defined by points of bodily contact) could be systematically linked to the chimpanzee's group identity, showed temporal consistency both within and between groups, and could not be accounted for by the arm-length differential between partners. GHC has been part of the behavioural repertoire of the chimpanzees under study for more than 9 years (surpassing durability criterion) and spread across generations (surpassing expansion criterion). These results strongly indicate that chimpanzees' social behaviour is not only motivated by innate predispositions and individual inclinations, but may also be partly cultural in nature. [ABSTRACT FROM AUTHOR]

Primate societies are characterized by bonded social relationships of a kind that are rare in other mammal taxa. These bonded relationships, which provide the basis for coalitions, are underpinned by an endorphin mechanism mediated by social grooming. However, bonded relationships of this kind impose constraints on the size of social groups that are possible. When ecological pressures have demanded larger groups, primates have had to evolve new mechanisms to facilitate bonding. This has involved increasing the size of vocal and visual communication repertoires, increasing the time devoted to social interaction and developing a capacity to manage two-tier social relationships (strong and weak ties). I consider the implications of these constraints for the evolution of human social communities and argue that laughter was an early evolutionary innovation that helped bridge the bonding gap between the group sizes characteristic of chimpanzees and australopithecines and those in later hominins. [ABSTRACT FROM AUTHOR]

Measuring rates of self-scratching provides a powerful index of anxiety in non-human primates, and investigating the relationship between self-scratching and dominance rank can shed light on the 'emotional costs' of holding different positions in the hierarchy. Here we explored the relationship between self-scratching rates and rank in wild adult female Barbary macaques (Macaca sylvanus) in Morocco. We found a significant correlation between rank and females' mean self-scratching rates over the study period, with subordinates showing higher rates of self-scratching. Analysis of temporal variation in females' self-scratching rates indicated that while these rates were related to measures of both grooming and aggression, the relationship between rank and self-scratching remained significant even after controlling for these effects. Our data suggest that lower ranked female Barbary macaques suffer higher levels of anxiety than more dominant individuals, and hence that there is an emotional cost associated with having low social status in this species. [ABSTRACT FROM AUTHOR]

Male mating success in a multimale-multifemale group can depend on several variables: body condition, dominance, coalitions, 'friendship,' or an exchange of services for mating access. Exchange patterns may also be determined by market effects or social relationships. We studied the mating tactics of males in a captive, multimale-multifemale group of rhesus macaques and the resulting patterns of mating and paternity to determine the influence of dominance rank, mating markets, and relationship quality on their mating tactics. Male rank was positively related to the total number of copulations and the number of mating partners, but did not explain male mating distribution completely. Moreover, male fertilization success was not related to male rank. Males did not exchange grooming for mating access on the same day and neither the supply nor the rank (as a proxy for quality) of receptive females affected the amount of male grooming, suggesting that market effects did not explain male mating access. However, there was a positive correlation between long-term grooming patterns of both males and females and mating access, indicating that social relationships were important for male mating access. Paternity data revealed that these social relationships were also important for male reproductive success. We conclude that both male rank and male-female 'friendship' determined male mating access in these rhesus macaques, but that 'friendship' was more important in determining paternity, emphasizing the importance of intersex social bonds in male mating success in multimale primate societies. [ABSTRACT FROM AUTHOR]

Social network analysis offers new tools to study the social structure of primate groups. We used social network analysis to investigate the cohesiveness of a grooming network in a captive chimpanzee group ( N = 17) and the role that individuals may play in it. Using data from a year-long observation, we constructed an unweighted social network of preferred grooming interactions by retaining only those dyads that groomed above the group mean. This choice of criterion was validated by the finding that the properties of the unweighted network correlated with the properties of a weighted network (i.e. a network representing the frequency of grooming interactions) constructed from the same data. To investigate group cohesion, we tested the resilience of the unweighted grooming network to the removal of central individuals (i.e. individuals with high betweenness centrality). The network fragmented more after the removal of individuals with high betweenness centrality than after the removal of random individuals. Central individuals played a pivotal role in maintaining the network's cohesiveness, and we suggest that this may be a typical property of affiliative networks like grooming networks. We found that the grooming network correlated with kinship and age, and that individuals with higher social status occupied more central positions in the network. Overall, the grooming network showed a heterogeneous structure, yet did not exhibit scale-free properties similar to many other primate networks. We discuss our results in light of recent findings on animal social networks and chimpanzee grooming. Am. J. Primatol. 73:758-767, 2011. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

We tested predictions following from the biological market paradigm using reciprocated grooming sessions among the adult females in a sooty mangabey, Cercocebus atys, group with 35 females (Ivory Coast) and in two groups of vervet monkeys, Chlorocebus aethiops (South Africa) with four and seven females, respectively. Closely ranked females often groomed frequently. The exchanges within such dyads were generally characterized by time matching, but the subordinates groomed for longer than their dominant partners. The reciprocal nature of over 90% of the grooming sessions allowed us to investigate ‘partner control’ strategies such as ‘parcelling’ and ‘raising the stakes’. Females of both species neither parcelled nor gradually invested more grooming in the course of sessions. Rather, the longer bouts of a grooming session were usually at the beginning of the session and the length of the first bout reliably predicted the length of the whole session for frequently grooming partners. Furthermore, we compared potential trust-building behaviour (or ‘strategies’) in frequent and infrequent grooming partners. We found that infrequent groomers of both species showed no signs of trust building and that the first bout they invested in a grooming session did not predict the session length. We conclude that each female has a good knowledge of her value as a grooming partner within each dyad and knows how much she has to invest to receive a satisfactory amount of grooming within the same session. [Copyright &y& Elsevier]

Abstract: There is a wide variation in the external eye morphology across species in primates, which is considered to reflect adaptation to ecological factors such as body size and habitat type. However, little attention has been paid to the contribution of social factors to the evolution of primate eye morphology. To explore this, we analyzed correlations among eye morphology, social factors (neocortex ratio and group size) and other factors (habitat type and body mass) in 30 living primate species including humans, using phylogenetically independent contrasts. The results indicated that parameters of primate eye morphology correlate with group size and neocortex ratio (Study 1). Further analysis of behavior indicated that the proportion of scanning with eyeball movement alone per total scanning correlated with group size and neocortex ratio (Study 2). The results support the view that the scanning with independent eyeball movement and its morphological basis is an adaptation to larger social groups. Communicative functions of the gaze signal other than the expression of aggression, observed in some primate species, may be based on features related to eye morphology. Furthermore, the evolution of a contact-free, social grooming function of gaze, especially predominant in humans, may reflect one extreme case of this kind of adaptation, which we call the “gaze-grooming” hypothesis. [Copyright &y& Elsevier]

The article presents research which examined the impact of potential intergroup conflict on intragroup affiliation in groups of breeding green woodhoopoes (Phoeniculus purpureus). The researcher recorded the beginning and the end of each allopreening and self-preening bouts between the members of the groups. He found that self-preening does not trigger or improve the conflict among the subjects.

Recent evidence suggests that female grooming kin bias in rhesus and Tibetan macaques varies within groups over time in a manner that is consistent with the time constraints model. Here we test the same hypothesis for Tonkean macaques, using data from a corral-living group collected between 1987 and 2002. We also use published data to ask whether time constraints can explain variation across the three macaque species and/or whether these species appear to show inherent differences in kin bias based on their species' social styles, as predicted by the phylogenetic model. Several predictions of the time constraints model were supported for Tonkean macaques: as the number of potential grooming partners increased, females groomed similar amounts, but displayed decreased per capita amounts of grooming, focused their grooming on a subset of potential partners, and displayed more intense grooming kin bias. Although numbers of potential partners affected all three species similarly, species differences in kin bias were sustained and were related to species social styles independently of numbers of potential partners. We suggest that grooming kin bias represents a social reaction norm, in which species display qualitatively similar, but inherently different ranges of response to the same current conditions. [ABSTRACT FROM AUTHOR]

Abstract: Grooming is a widespread activity throughout the animal kingdom, but in primates (including humans) social grooming, or allo-grooming (the grooming of others), plays a particularly important role in social bonding which, in turn, has a major impact on an individual''s lifetime reproductive fitness. New evidence from comparative brain analyses suggests that primates have social relationships of a qualitatively different kind to those found in other animal species, and I suggest that, in primates, social grooming has acquired a new function of supporting these. I review the evidence for a neuropeptide basis for social bonding, and draw attention to the fact that the neuroendrocrine pathways involved are quite unresolved. Despite recent claims for the central importance of oxytocin, there is equally good, but invariably ignored, evidence for a role for endorphins. I suggest that these two neuropeptide families may play different roles in the processes of social bonding in primates and non-primates, and that more experimental work will be needed to tease them apart. [Copyright &y& Elsevier]

Several hypotheses have been proposed to explain the evolution of altruistic behaviours. Their relative roles in explaining actual cases of animal altruism are, however, unclear. In particular, while kin selection is widely believed to have a pervasive influence on animal behaviour, reciprocity is generally thought to be rare. Despite this general agreement, there has been no direct test comparing the relative roles of kinship and reciprocity in explaining animal altruism. In this paper, we report on the results of such a test based on a meta-analysis of allogrooming in primates, grooming being probably the most common altruistic behaviour among mammals. In direct contrast to the prevailing view, reciprocity played a much larger role than kinship in explaining primate allogrooming. These results point to a more significant role of reciprocity in the evolution of animal altruism than is generally acknowledged. Ecology Letters (2010) 13: 45–50 [ABSTRACT FROM AUTHOR]

Most primates are intensely social and spend a large amount of time servicing social relationships. In this study, we use social network analysis to examine the relationship between primate group size, total brain size, neocortex ratio and several social network metrics concerned with network cohesion. Using female grooming networks from a number of Old World monkey species, we found that neocortex size was a better predictor of network characteristics than endocranial volumes. We further found that when we controlled for group size, neocortex ratio was negatively correlated with network density, connectivity, relative clan size and proportional clan membership, while there was no effect of neocortex ratio on change in connectivity following the removal of the most central female in the network. Thus, in species with larger neocortex ratios, females generally live in more fragmented networks, belong to smaller grooming clans and are members of relatively fewer clans despite living in a closely bonded group. However, even though groups are more fragmented to begin with among species with larger neocortices, the removal of the most central individual does cause groups to fall apart, suggesting that social complexity may ultimately involve the management of highly fragmented social groups while at the same time maintaining overall social cohesion. These results emphasize a need for more detailed brain data on a wider sample of primate species. [ABSTRACT FROM AUTHOR]

The scarcity of evidence for contingent reciprocity has led to a growing interest in how market forces shape the distribution of exchanges in animal groups. In a biological market, supply and demand determines the value of an exchange, and individuals choose to trade with the partner offering the highest value. Partners maximize their immediate benefits without the need to monitor the balance of their exchange over time. Applied to grooming exchanges in primate groups, a market model predicts that females will primarily balance the amount of grooming they trade within single bouts, particularly when all partners offer similar value. If some partners can offer other benefits, like reduced aggression, females may exchange grooming for those benefits. In such cases, grooming will not be evenly balanced within bouts. Here, we examine the patterning of grooming in a group of free-ranging olive baboons (Papio anubis). In contrast to predictions derived from a biological market model, two-thirds of all grooming bouts in this group were completely one-sided and females did not consistently provide more grooming to higher-ranking partners. Grooming was more evenly balanced across multiple bouts than within single bouts, suggesting that females are not constrained to complete exchanges within single transactions. [ABSTRACT FROM AUTHOR]

Studies investigating the relation between allogrooming and social rank in capuchin monkeys (genus Cebus) have yielded inconsistent results. In this study, we investigated the relation between grooming, agonistic support, aggression and social rank in a captive group of tufted capuchin monkeys (C. apella). Differently from most previous studies, we based our analyses on a relatively large database and studied a group with known genealogical relationships. Tufted capuchin females did not exchange grooming for rank-related benefits such as agonistic support or reduced aggression. Coherently with this picture, they did not groom up the hierarchy and did not compete for accessing high-ranking grooming partners. It is suggested that a small group size, coupled with a strong kin bias, may make the exchange of grooming for rank-related benefits impossible or unprofitable, thus eliminating the advantages of grooming up the hierarchy. We provide several possible explanations for the heterogeneity of results across capuchin studies that have addressed similar questions. Am. J. Primatol. 71:101–105, 2009. © 2008 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

To assess what female Sichuan snub-nosed monkeys ( Rhinopithecus roxellana) gain from allowing others to care for their infants, we collected behavioral data on 12 mother-infant dyads at Zhouzhi National Nature Reserve in the Qinling Mountains, China. Mothers’ feeding time significantly increased when infants were cared for by other group members versus when they were cared for by the mothers themselves. The time mothers spent autogrooming and receiving grooming also increased when they were temporarily relieved of maternal duties; however, mothers did not groom other individuals more when they were not encumbered by infants. There are several benefits that mothers gain from having helpers care for their infants: They gain more time to feed and thus increase their feeding efficiency. Mothers have more time to engage in hygienic and maintenance activities because they autogroom and receive allogrooming more. Lastly, mothers save energy when their infants are with helpers. Wild Sichuan snub-nosed monkey mothers meet their basic survival and maintenance needs because of helping behavior. [ABSTRACT FROM AUTHOR]

Grooming is a complex set of motor actions, common in highly social primates. We tested for asymmetries in hand use during unimanual and bimanual allogrooming in 215 captive chimpanzees. In addition to hand use, we coded in the ethogram whether the manual grooming action co-occurred with the use of the mouth. Overall, grooming did not elicit strong handedness at the individual level, but there is a small yet significant population-level right-hand bias for bimanual grooming. Mouth use during grooming had no influence on hand use. A comparison of the findings with previously published data on handedness for grooming in wild chimpanzees suggests that wild apes are more right-handed than captive individuals are for allogrooming. Collectively, the results suggest that role differentiation of the hands is an important factor in the assessment of handedness for grooming, and perhaps additional manual actions of chimpanzees and other primates. [ABSTRACT FROM AUTHOR]

Female long-tailed macaques are attracted to infants and frequently groom mothers bearing them. Such grooming often involves the groomer contacting the infant and may be a trade of grooming for infant handling. To identify if grooming and infant handling are directly traded, I collected samples on times after female-to-mother grooming and on interactions in which a female groomed a mother and contacted her infant. I determined that grooming tended to promote an exchange with infant handling and that the supply of available infants was related to how long a female groomed a mother. Grooming interactions were longer when infants were scarce in the surrounding social environment than when they were abundant, indicating a possible supply-and-demand effect. This supports that grooming may be payment for infant handling. Grooming-infant handling interchanges tended to be unidirectional as mothers usually did not reciprocate grooming. Instead, infant contact occurred. A larger proportion of grooming-infant handling interchanges involved younger infants, but infant age did not seem to influence grooming durations. The length of female-to-mother grooming had no observable effect on handling time. Lower-ranked females groomed higher-ranked mothers and their infants longer than vice versa. Moreover, it was possible to predict up-rank grooming via supply and demand better than down-rank grooming. There was no observable influence of kinship on grooming-infant handling interchange. These results support the conclusion that grooming and infant handling may be traded. Grooming promoted infant handling, while supply and rank predicted the grooming payment a female would offer to access an infant. [ABSTRACT FROM AUTHOR]

In order to examine the presence of long-term grooming relationships among unrelated females, grooming interactions of 18 adult females (range: 16–32 years) in a free-ranging group of Japanese monkeys (Macaca fuscata) were recorded in 2003 and compared with those recorded 10 years earlier, i.e., in 1993. In 2003, on average, each female who had survived the 10 years had grooming interactions with 2.2 surviving old partners with whom she was recorded to have grooming interactions in 1993, 3.5 females related to the surviving old partners, and 4.5 unrelated females who were other than the surviving old partners or their related females. By calculating the ratio of actual grooming partners to available females in 2003, we concluded that females had a greater possibility of selecting surviving old partners as their grooming partners than other unrelated partners, and that they also had a greater possibility of selecting females related to surviving old partners than females other than surviving old partners and their related females. These findings indicate that with regard to grooming relationships, female Japanese monkeys are basically conservative, showing a tendency to concentrate their grooming interactions on closely related females and certain familiar unrelated females such as surviving old partners and some females closely related to these partners. At the same time, however, female Japanese monkeys also showed a progressive trait for grooming since they formed grooming relationships with new partners. The necessity of long-term psychological bonding for long-term grooming relationships between unrelated females is discussed in this work. Am. J. Primatol. 69:652–663, 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

In a mixed-sex, captive group of hamadryas baboons (Papio hamadryas hamadryas ) we investigated whether female grooming relationships are affected by their dominance ranks. Seyfarth’s [1977] grooming for support model and Barrett et al.’s [1999] biological market model both predict that in primate groups where competition for monopolizable resources is high, grooming among females is based, at least partly, on the interchange of grooming for rank-related benefits, and that rank thus influences the distribution of grooming in females. Contrary to this prediction, our results show that despite the existence of a linear dominance hierarchy, rather strict dominance relationships, and high food-related aggression rates, grooming among female hamadryas baboons is not affected by rank and is only exchanged for itself. This is understandable since rank differences in our study group only result in differential access to limited, preferred food items that are not actively shared. Although some females are more likely to tolerate one another at the food pile, this tolerance is not determined by their grooming efforts and interchange of grooming for rank-related benefits does not occur. We conclude that female hamadryas baboons groom others in order to be groomed by them, which is supported by our observation that grooming reciprocity within a dyad increases when more grooming occurs in this dyad. Our results indicate that grooming is indeed a valuable commodity in itself, probably because of its stress- and tension-reducing effect. Based on our findings, the existing groom trade model is extended to include circumstances in which monopolizable resources are available but are not traded for grooming. Am. J. Primatol. 55:25–42, 2001. © 2001 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

We examined the hygienic functional hypothesis of allogrooming in two captive groups (N = 9 and N = 8) of white-crowned mangabeys (Cercocebus torquatus lunulatus ) by analyzing the corporeal distribution of allogrooming solicitations according to the variable degree of accessibility of the various body sites. We used focal-animal sampling and continuous recording and nonparametric statistics (sing test and χ[sup 2] ). The fact that in both groups more allogrooming was solicited to sites associated with accessibility problems is consistent with the hygienic functional hypothesis of allogrooming. In any case, there are two facts that suggest that this hypothesis cannot account for all the characteristics of such behavior: 1) the strong distributional selectivity shown by allogrooming solicitations—they concentrated primarily on dorsal and caudal regions instead of those difficult to reach or inaccessible on the whole—and 2) the significant role played by sex in the intragroup distribution of anogenital solicitations. Supporting the multifunctional nature of allogrooming, we find very appealing the ritualization hypothesis, according to which the allogrooming performed on certain body sites would have acquired a sociocommunicative meaning. [ABSTRACT FROM AUTHOR]

Reciprocity and social bonding hypotheses were evaluated as explanations for observed patterns of social grooming in assamese macaques (Macaca assamensis ). In accordance with social bonding, females, as the long-term residents of this matrifocal group, groomed each other and juveniles more often than males groomed one another or juveniles. On the other hand, males groomed females more often and for longer durations than females groomed males and, whereas both males and females groomed juveniles more often than juveniles groomed them, juveniles groomed their elders for longer durations. Male grooming of females did not seem directly related to matings as males are single mount ejaculators and use coercive mating tactics. Male grooming of females could not be accounted for in terms of reciprocity; it was not a simple function of dominance. Although both sexes groomed subordinate females more than vice versa, males groomed dominant males more and females groomed subordinate males more than they received grooming from them. Grooming was concluded to function to establish and maintain affiliative social bonds rather than as a specific mechanism to obtain matings or any other specific reciprocation in terms of services or favors. Am. J. Primatol. 50:77–85, 2000. © 2000 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Abstracts 1-33 [ABSTRACT FROM AUTHOR]

Human epidemiological studies have suggested that social variables can modulate the effects of stress on the immune system, and this concept has been gaining increasing attention with positive results emerging from empirical studies using nonhuman primates over the last two decades. Results from a previous study in rhesus monkeys suggested that receiving grooming positively affected recovery, of T-helper and T-suppressor cells following the initial stress associated with group formation, and this covaried with high dominance rank. Thus, the present study was undertaken in order to determine: (1) if the stress effect of formation could be replicated in another species and (2) if social behaviors or dominance rank, given that formation is a stressor, might independently correlate with physiological recovery from the stressor. Eight adult female pigtail macaques were moved from individual cages and simultaneously introduced into an outdoor enclosure along with an adult male, while eight weight-matched controls remained in individual caging. Behavioral data were collected during the introduction and over 4 weeks thereafter. Blood samples were collected prior to and at intervals for 4 weeks following formation. Compared to control subjects, the test subjects showed an increase in basal cortisol secretion (+ 28.9%) and a significant decrease in T-helper cells (-33.6%). T-suppressor cells (-30.8%), and B cells (-22,5%), while there was a significant increase in white blood cells (+29.5%) 24 hr following formation. When dominance rank and seven behavioral categories were analyzed, only the frequency of receiving grooming significantly predicted change, with animals who received a greater frequency of grooms showing a lesser negative percent change from baseline in the absolute number of T-helper cells I week following formation. The establishment of a dominance hierarchy, apparent within 1 week, was accomplished with no serious fighting and a complete absence of wounding or trauma, suggesting that psychosocial stress was responsible for the physiological changes observed. [ABSTRACT FROM AUTHOR]

Abstract: Grueter et al. have recently claimed that grooming time in primates is best explained by terrestriality, which they take to be a proxy for hygiene demand. We suggest that their results arise from a confound between terrestriality and other aspects of sociality, combined with a number of conceptual and sampling problems. [Copyright &y& Elsevier]

In highly social species, like primates, oxytocin plays an important role in cooperation, and in the formation and maintenance of social relationships. Despite recent interest in the relationship between oxytocin and social behavior in nonhuman primates, relatively little is known about endogenous oxytocin in social New World Monkeys. In this paper, we investigate the relationship between oxytocin and affiliative behaviors in socially‐housed captive capuchin monkeys (Sapajus [Cebus] apella) by first validating methods of analysis of urinary oxytocin in this species and, second, examining the effects of grooming and fur‐rubbing behavior on oxytocin concentrations and further affiliative behavior. In the validation, we found that intranasal exogenous oxytocin significantly increased urinary oxytocin 15–60 min post‐administration. Oxytocin was also implicated in both grooming and fur‐rubbing behaviors. We found that oxytocin concentrations increased after subjects engaged in grooming or fur‐rubbing. In addition, we found that fur‐rubbing influenced affiliative behaviors, both during and after a social fur‐rubbing bout. While individuals spent more time in contact and proximity while fur‐rubbing, immediately following the fur‐rubbing event (15–30 min afterwards) all affiliative behaviors decreased. This supports previous research that oxytocin may, in fact, initially be related to increased social distance in this species. Yet, an increase in all affiliative behaviors 30–45 min after the onset of fur‐rubbing suggests that fur‐rubbing, like grooming, may ultimately function to strengthen social relationships. Overall, these results support a critical role for oxytocin in affiliative behaviors that maintain and strengthen social relationships in capuchin monkeys, and highlight the complexity of the interactions among oxytocin, affiliative behaviors, and social bonding. Exogenous oxytocin administration, grooming, and fur‐rubbing behavior increased urinary oxytocin in capuchins. Despite increases in oxytocin after fur‐rubbing, affiliative behaviors initially decreased in the time immediately following the bout; however, 30 minutes after the fur‐rubbing bout, subjects engaged in increased proximity, contact, and grooming. Results support the hypothesis that the adaptive function of oxytocin is to strengthen social bonds; however, oxytocin may have species and context‐specific effects on affiliative behaviors. [ABSTRACT FROM AUTHOR]

Abstract: Some animals conserve body heat through physical contact with conspecifics (i.e., huddling) under cold climate conditions. However, the factors that promote huddle partner selection have not been clarified. We hypothesized that exchanging grooming for huddling is a beneficial strategy used by female Japanese macaques (Macaca fuscata) to withstand cold temperatures. In this study, we undertook focal sampling of 17 female macaques at Katsuyama, Okayama Prefecture, Japan, between April 2012 and March 2013. We used generalized linear mixed models and determined influential factors based on the Akaike information criterion. As a result, we found that female Japanese macaques were likely to participate in grooming interactions before huddling with adult females, but that they rarely did so before huddling with their young (1-year-old or younger) offspring. In particular, adult females tended to huddle with other adult females after unreciprocated grooming bouts. Moreover, they solicited return grooming less frequently when females huddled after grooming interactions than when they did not huddle after grooming interactions. Finally, we evaluated whether grooming improved huddling position. Immediately after grooming, females huddled at advantageous positions more often than they huddled without grooming, and relative benefit by huddling position in the groomer was likely to be larger than the groomee. In contrast, when females huddled after reciprocal grooming, females tended to huddle in positions that were equally beneficial to both females. Overall, our results suggest that female Japanese macaques, particularly those without young offspring, exchange grooming for huddling with other adult females.Significance statement: Huddling is a thermoregulatory behavior performed under cold climate conditions; however, the factors promoting huddle partner selection are unclear. In several animal species, including primates, individuals exchange grooming for reciprocal grooming or other social benefits, such as access to infants and agonistic support. This study showed that during winter, female Japanese macaques obtain huddling benefits in exchange for grooming. However, females with young offspring were unlikely to use grooming to huddle with adult females because their offspring act as huddling partners. Thus, the use of grooming by Japanese macaques as a payment is flexible, depending on the needed benefits of the individuals. To our knowledge, this is the first study to suggest that huddling is a potential commodity that females trade in exchange for grooming. [ABSTRACT FROM AUTHOR]