Responses to social and environmental stress are attenuated by strong male bonds in wild macaques

Differentiated Social Relationships and the Pace-of-Life-History

When selection is imposed by both social and ecological environments, the costs and benefits of social relationships can depend on life-history strategy. We argue that the formation and maintenance of differentiated social relationships will prevail in species and individuals with slow life histories. Social behaviours that benefit survival can promote slower life histories. Meanwhile, longer lifespan promotes the development of strong and stable social bonds by allowing fitness payoffs to be postponed. Differentiated social behaviours should be favoured for fast life histories only when they promote the rate of reproduction. Finally, associations between life-history strategies and other traits (e.g., personality) provide a mechanism to drive inter-individual variation in social relationships, making life-history important for sociality across taxonomic scales.

Social bonds, social status and survival in wild baboons: a tale of two sexes

People who are more socially integrated or have higher socio-economic status live longer. Recent studies in non-human primates show striking convergences with this human pattern: female primates with more social partners, stronger social bonds or higher dominance rank all lead longer lives. However, it remains unclear whether social environments also predict survival in male non-human primates, as it does in men. This gap persists because, in most primates, males disperse among social groups, resulting in many males who disappear with unknown fate and have unknown dates of birth. We present a Bayesian model to estimate the effects of time-varying social covariates on age-specific adult mortality in both sexes of wild baboons. We compare how the survival trajectories of both sexes are linked to social bonds and social status over the life. We find that, parallel to females, male baboons who are more strongly bonded to females have longer lifespans. However, males with higher dominance rank for their age appear to have shorter lifespans. This finding brings new understanding to the adaptive significance of heterosexual social bonds for male baboons: in addition to protecting the male's offspring from infanticide, these bonds may have direct benefits to males themselves. This article is part of the theme issue 'Evolution of the primate ageing process'.

Observing the unwatchable: Integrating automated sensing, naturalistic observations and animal social network analysis in the age of big data

In the 4.5 decades since Altmann (1974) published her seminal paper on the methods for the observational study of behaviour, automated detection and analysis of social interaction networks have fundamentally transformed the ways that ecologists study social behaviour. Methodological developments for collecting data remotely on social behaviour involve indirect inference of associations, direct recordings of interactions and machine vision. These recent technological advances are improving the scale and resolution with which we can dissect interactions among animals. They are also revealing new intricacies of animal social interactions at spatial and temporal resolutions as well as in ecological contexts that have been hidden from humans, making the unwatchable seeable. We first outline how these technological applications are permitting researchers to collect exquisitely detailed information with little observer bias. We further recognize new emerging challenges from these new reality-mining approaches. While technological advances in automating data collection and its analysis are moving at an unprecedented rate, we urge ecologists to thoughtfully combine these new tools with classic behavioural and ecological monitoring methods to place our understanding of animal social networks within fundamental biological contexts.

Anthropogenic Change Alters Ecological Relationships via Interactive Changes in Stress Physiology and Behavior within and among Organisms

Anthropogenic change has well-documented impacts on stress physiology and behavior across diverse taxonomic groups. Within individual organisms, physiological and behavioral traits often covary at proximate and ultimate timescales. In the context of global change, this means that impacts on physiology can have downstream impacts on behavior, and vice versa. Because all organisms interact with members of their own species and other species within their communities, the effects of humans on one organism can impose indirect effects on one or more other organisms, resulting in cascading effects across interaction networks. Human-induced changes in the stress physiology of one species and the downstream impacts on behavior can therefore interact with the physiological and behavioral responses of other organisms to alter emergent ecological phenomena. Here, we highlight three scenarios in which the stress physiology and behavior of individuals on different sides of an ecological relationship are interactively impacted by anthropogenic change. We discuss host-parasite/pathogen dynamics, predator-prey relationships, and beneficial partnerships (mutualisms and cooperation) in this framework, considering cases in which the effect of stressors on each type of network may be attenuated or enhanced by interactive changes in behavior and physiology. These examples shed light on the ways that stressors imposed at the level of one individual can impact ecological relationships to trigger downstream consequences for behavioral and ecological dynamics. Ultimately, changes in stress physiology on one or both sides of an ecological interaction can mediate higher-level population and community changes due in part to their cascading impacts on behavior. This framework may prove useful for anticipating and potentially mitigating previously underappreciated ecological responses to anthropogenic perturbations in a rapidly changing world.

Testosterone and cortisol are negatively associated with ritualized bonding behavior in male macaques

Neuroendocrine research on the formation of social bonds has primarily focused on the role of nonapeptides. However, steroid hormones often act simultaneously to either inhibit or facilitate bonding. Testosterone is proposed to mediate a trade-off between male mating effort and nurturing behavior; therefore, low levels are predicted during periods of nurturing infant care and social bonding. In species where social bonding and support regulates hypothalamic-pituitary-adrenal axis activity, we also expect glucocorticoid levels to be low during bonding periods. We investigated how immunoreactive urinary testosterone (iuT) and cortisol (iuC) were related to triadic male-infant-male interactions - a ritualized male bonding behavior - as well as infant care in male Barbary macaques (Macaca sylvanus). We collected >3000 h of behavioral observation data during full-day focal animal follows from 14 adult males and quantified iuT and iuC from 650 urine samples. iuT was negatively correlated with rates of triadic interactions within subjects, but positively correlated between subjects. iuC was negatively correlated with triadic interactions both within and between subjects. Time spent caring for infants was positively correlated to both iuT and iuC within subjects, but not between subjects. The observed negative relationship between iuT and triadic interactions within subjects may be beneficial to lower competitive tendencies between adult males and to not inhibit bond formation. However, the positive correlation of iuT with triadic interactions between subjects was unexpected. We speculate that it could be due to a link between triadic interactions and coalition formation. A negative relationship between triadic interactions and iuC could reflect increased bonding and perceived social support as triadic interactions predict future coalition formation in this species, or reflect buffered tensions between males. The positive relationship of iuT and iuC with infant care suggests that the handling of infants may be less nurturing but rather protective or competitive in this species. Measuring steroid hormones in relation to bonding and nurturing can help us interpret behaviors within the ecological contexts that they occur.

The Neurobiology of Social Distance

Never before have we experienced social isolation on such a massive scale as we have in response to coronavirus disease 2019 (COVID-19). However, we know that the social environment has a dramatic impact on our sense of life satisfaction and well-being. In times of distress, crisis, or disaster, human resilience depends on the richness and strength of social connections, as well as on active engagement in groups and communities. Over recent years, evidence emerging from various disciplines has made it abundantly clear: perceived social isolation (i.e., loneliness) may be the most potent threat to survival and longevity. We highlight the benefits of social bonds, the choreographies of bond creation and maintenance, as well as the neurocognitive basis of social isolation and its deep consequences for mental and physical health.

Dynamics and determinants of glucocorticoid metabolite concentrations in wild Verreaux's sifakas

Glucocorticoids have wide-ranging effects on animals' behaviour, but many of these effects remain poorly understood because numerous confounding factors have often been neglected in previous studies. Here, we present data from a 2-year study of 7 groups of wild Verreaux's sifakas (Propithecus verreauxi), in which we examined concentrations of faecal glucocorticoid metabolites (fGCMs, n = 2350 samples) simultaneously in relation to ambient temperatures, food intake, rank, reproduction, adult sex ratios, social interactions, vigilance and self-scratching. Multi-variate analyses revealed that fGCM concentrations were positively correlated with increases in daily temperature fluctuations and tended to decrease with increasing fruit intake. fGCM concentrations increased when males were sexually mature and began to disperse, and dominant males had higher fGCM concentrations than subordinate males. In contrast to males, older females showed a non-significant trend to have lower fGCM levels, potentially reflecting differences in male and female life-history strategies. Reproducing females had the highest fGCM concentrations during late gestation and had higher fGCM levels than non-reproducing females, except during early lactation. Variation in fGCM concentrations was not associated with variation in social interactions, adult sex ratios, vigilance and self-scratching. Altogether, we show that measures of glucocorticoid output constitute appropriate tools for studying energetic burdens of ecological and reproductive challenges. However, they seem to be insufficient indicators for immediate endocrinological responses to social and nonsocial behaviours that are not directly linked to energy metabolism.

Structure and function in human and primate social networks: implications for diffusion, network stability and health

The human social world is orders of magnitude smaller than our highly urbanized world might lead us to suppose. In addition, human social networks have a very distinct fractal structure similar to that observed in other primates. In part, this reflects a cognitive constraint, and in part a time constraint, on the capacity for interaction. Structured networks of this kind have a significant effect on the rates of transmission of both disease and information. Because the cognitive mechanism underpinning network structure is based on trust, internal and external threats that undermine trust or constrain interaction inevitably result in the fragmentation and restructuring of networks. In contexts where network sizes are smaller, this is likely to have significant impacts on psychological and physical health risks.

The Impact of Social and Behavioral Factors on Reproducibility in Terrestrial Vertebrate Models

The use of animal models remains critical in preclinical and translational research. The reliability of the animal models and aspects of their validity is likely key to effective translation of findings to medicine. However, despite considerable uniformity in animal models brought about by control of genetics, there remain a number of social as well as innate and acquired behavioral characteristics of laboratory animals that may impact on research outcomes. These include the effects of strain and genetics, age and development, sex, personality and affective states, and social factors largely brought about by housing and husbandry. In addition, aspects of the testing environment may also influence research findings. A number of considerations resulting from the animals' innate and acquired behavioral characteristics as well as their social structures are described. Suggestions for minimizing the impact of these factors on research are provided.

An understanding of third-party friendships in a tolerant macaque

Complex societies are shaped by social relationships between multiple individuals. The pressure to track these relationships has driven the evolution of social cognition in primates. Importantly, it can be adaptive to track not only personal relationships, but also those established between third-parties. Primates have knowledge about others’ dominance hierarchies and kinship, but we do not know to what extent they also understand friendships. In a playback experiment, Tonkean macaques were presented with simulated conflicts involving third-party female dyads who were established friends or non-friends. Hearing a conflict between friends elicited a stronger behavioural response in listeners (i.e. an increase in looking time) compared to hearing a conflict between non-friends. Conflicts between friends are likely to represent a greater disruption of the social group and structure of the network, and therefore this difference in response may represent an adaptive strategy employed by the macaques to selectively monitor important social interactions in the group. These findings provide evidence that Tonkean macaques (and potentially other primates) can classify the relationships of others based on their degree of friendship and additionally, confirms the important role friendships have within the societies of social primates.

Cooperation with closely bonded individuals reduces cortisol levels in long-tailed macaques

Many animal species cooperate with conspecifics in various social contexts. While ultimate causes of cooperation are being studied extensively, its proximate causes, particularly endocrine mechanisms, have received comparatively little attention. Here, we present a study investigating the link between the hormone cortisol, cooperation and social bonds in long-tailed macaques (Macaca fascicularis). We tested 14 macaques in a dyadic cooperation task (loose-string paradigm), each with two partners of different social bond strength and measured their salivary cortisol before and after the task. We found no strong link between the macaques' cortisol level before the task and subsequent cooperative success. By contrast, we did find that the act of cooperating in itself led to a subsequent decrease in cortisol levels, but only when cooperating with closely bonded individuals. Two control conditions showed that this effect was not due to the mere presence of such an individual or the pulling task itself. Consequently, our study shows an intricate way in which the hypothalamic-pituitary-adrenal axis is involved in cooperation. Future studies should reveal whether and how our findings are driven by the anxiolytic effect of oxytocin, which has been associated with social bonding.

Sulawesi Crested Macaque (Macaca nigra) Grooming Networks Are Robust to Perturbation While Individual Associations Are More Labile

Social and environmental disturbance occurs naturally, and species in bonded social groups should be resilient to it. Empirical evidence of social responses to disturbance in primates, however, remains limited. We constructed social networks using group-level scan samples (N = 299) to test the robustness of grooming networks in a captive group of 20 Sulawesi crested macaques (Macaca nigra) to two management interventions involving environmental and social disturbance. During the first, the institution removed six castrated males and one female, contracepted six of the nine remaining females, and moved the group to a new enclosure. The second involved the introduction of a novel, reproductive male five weeks later. Networks remained stable following the first intervention. However, after introduction of the male, the number of grooming partners and the frequency of grooming with non-maternal kin increased in female-only networks. We observed less marked increases in the grooming frequency and number of grooming partners in whole group networks. Ten weeks later, network structure was more similar to that of pre-intervention networks than post-intervention networks. Our results suggest that reproductive males play a more important role in structuring Sulawesi crested macaque social networks than castrated males, as networks expanded and relationships between non-maternal kin occurred more frequently after introduction of the reproductive male. However, network responses to interventions appeared to be temporary as networks following a period of acclimation more closely resembled pre-intervention networks than post-intervention networks. Our study demonstrates the utility of social network analysis for understanding the impact of disturbance on stable social groups.

Oxytocin increases after affiliative interactions in male Barbary macaques

Mammals living in stable social groups often mitigate the costs of group living through the formation of social bonds and cooperative relationships. The neuropeptide hormone oxytocin (OT) is proposed to promote both bonding and cooperation although only a limited number of studies have investigated this under natural conditions. Our aim was to assess the role of OT in bonding and cooperation in male Barbary macaques (Macaca sylvanus). First, we tested for an effect of affiliation - grooming and triadic male-infant-male interactions - with bond and non-bond partners on urinary OT levels. Second, we tested whether grooming interactions (and thus increased OT levels) increase a male's general propensity to cooperate in polyadic conflicts. We collected >4000 h of behavioral data on 14 adult males and measured OT levels from 139 urine samples collected after affiliation and non-social control periods. Urinary OT levels were higher after grooming with any partner. By contrast, OT levels after male-infant-male interactions with any partner or with bond partners were not different from controls but were higher after interactions with non-bond partners. Previous grooming did not increase the likelihood of males to support others in conflicts. Collectively, our results support research indicating that OT is involved in the regulation of adult affiliative relationships. However, our male-infant-male interaction results contradict previous studies suggesting that it is affiliation with bond rather than non-bond partners that trigger the release of OT. Alternatively, OT levels were elevated prior to male-infant-male interactions thus facilitating interaction between non-bond partners. The lack of an association of grooming and subsequent support speaks against an OT linked increase in the general propensity to cooperate.

Energy balance but not competitive environment corresponds with allostatic load during development in an Old World monkey

Primates develop slowly relative to their body size, a pattern posited to result from ecological risk aversion. Little is known, however, about how energy balance contributes to allostatic load in juveniles. Using data collected over 8 consecutive months, we examined variation in energy balance (as measured by urinary C-peptide) and how energy balance, life history status, and social competition related to allostatic load (as measured by deviation from baseline fecal glucocorticoid metabolites, dfGCs) in 41 wild juvenile blue monkeys from 3 social groups. Juvenile energy balance was higher among females, older juveniles, when ripe fruit was more available, and when rainfall was lower. Energy balance, but not life history or competitive environments, predicted dfGC concentrations, such that juveniles generally had lower mean dfGCs when they had higher energy balance. An additional exploratory analysis of how dfGCs relate to social strategies revealed that subjects had lower dfGCs when they groomed less, and played more. Time spent grooming interacted with energy balance in predicting dfGC concentrations, so that individuals that groomed more actually had higher dfGCs when they had higher energy balance. Together these results reveal that energetic deficiencies are a true ecological risk factor in blue monkeys, and suggest that navigating the social environment via overt affiliative behavior is potentially both a stress-relieving and stress-inducing endeavor during development.

Impact of anthropogenic factors on affiliative behaviors among bonnet macaques

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.

Adolescent male chimpanzees (Pan troglodytes) form social bonds with their brothers and others during the transition to adulthood

Social relationships play an important role in animal behavior. Bonds with kin provide indirect fitness benefits, and those with nonkin may furnish direct benefits. Adult male chimpanzees (Pan troglodytes) exhibit social bonds with maternal brothers as well as unrelated adult males, facilitating cooperative behavior, but it is unclear when these bonds develop. Prior studies suggest that social bonds emerge during adolescence. Alternatively, bonds may develop during adulthood when male chimpanzees can gain fitness benefits through alliances used to compete for dominance status. To investigate these possibilities and to determine who formed bonds, we studied the social relationships of adolescent and young adult male chimpanzees (N = 18) at Ngogo in Kibale National Park, Uganda. Adolescent male chimpanzees displayed social bonds with other males, and they did so as often as did young adult males. Adolescent and young adult males frequently joined subgroups with old males. They spent time in proximity to and grooming with old males, although they also did so with their age peers. Controlling for age and age difference, males formed strong association and proximity relationships with their maternal brothers and grooming relationships with their fathers. Grooming bonds between chimpanzee fathers and their adolescent and young adult sons have not been documented before and are unexpected because female chimpanzees mate with multiple males. How fathers recognize their sons and vice versa remains unclear but may be due to familiarity created by relationships earlier in development.

Primate Infectious Disease Ecology: Insights and Future Directions at the Human-Macaque Interface

Global population expansion has increased interactions and conflicts between humans and nonhuman primates over shared ecological space and resources. Such ecological overlap, along with our shared evolutionary histories, makes human-nonhuman primate interfaces hot spots for the acquisition and transmission of parasites. In this chapter, we bring to light the importance of human-macaque interfaces in particular as hot spots for infectious disease ecological and epidemiological assessments. We first outline the significance and broader objectives behind research related to the subfield of primate infectious disease ecology and epidemiology. We then reveal how members of the genus Macaca, being among the most socioecologically flexible and invasive of all primate taxa, live under varying degrees of overlap with humans in anthropogenic landscapes. Thus, human-macaque interfaces may favor the bidirectional exchange of parasites. We then review studies that have isolated various types of parasites at human-macaque interfaces, using information from the Global Mammal Parasite Database (GMPD: http://www.mammalparasites.org/). Finally, we elaborate on avenues through which the implementation of both novel conceptual frameworks (e.g., Coupled Systems, One Health) and quantitative network-based approaches (e.g., social and bipartite networks, agent-based modeling) may potentially address some of the critical gaps in our current knowledge of infectious disease ecology at human-primate interfaces.

Climate induced stress and mortality in vervet monkeys

As the effects of global climate change become more apparent, animal species will become increasingly affected by extreme climate and its effect on the environment. There is a pressing need to understand animal physiological and behavioural responses to climatic stressors. We used the reactive scope model as a framework to investigate the influence of drought conditions on vervet monkey (Chlorocebus pygerythrus) behaviour, physiological stress and survival across 2.5 years in South Africa. Data were collected on climatic, environmental and behavioural variables and physiological stress via faecal glucocorticoid metabolites (fGCMs). There was a meaningful interaction between water availability and resource abundance: when food availability was high but standing water was unavailable, fGCM concentrations were higher compared to when food was abundant and water was available. Vervet monkeys adapted their behaviour during a drought period by spending a greater proportion of time resting at the expense of feeding, moving and social behaviour. As food availability decreased, vervet mortality increased. Peak mortality occurred when food availability was at its lowest and there was no standing water. A survival analysis revealed that higher fGCM concentrations were associated with an increased probability of mortality. Our results suggest that with continued climate change, the increasing prevalence of drought will negatively affect vervet abundance and distribution in our population. Our study contributes to knowledge of the limits and scope of behavioural and physiological plasticity among vervet monkeys in the face of rapid environmental change.

Measuring urinary cortisol and testosterone levels in male Barbary macaques: A comparison of EIA and LC-MS

The development of methods to quantify hormones from non-invasively collected samples such as urine or feces has facilitated endocrinology research on wild-living animals. To ensure that hormone measurements are biologically meaningful, method validations are strongly recommended for each new species or sample matrix. Our aim was to validate three commonly used enzyme immunoassays (EIA), one for analysis of cortisol and two for analysis of testosterone, to assess adrenocortical and gonadal endocrine activity, respectively, from the urine of male Barbary macaques. We compared EIA and liquid chromatography-mass spectrometry (LC-MS) results to determine if the EIA measurements truly reflect levels of the target hormone and to determine if antibody cross-reactivities with other steroids were potentially confounding results. Furthermore, we conducted a biological validation of testosterone to ensure that both EIA and LC-MS were able to capture physiologically meaningful differences in hormone levels. We found that cortisol measured by EIA correlated strongly with cortisol measured by LC-MS in both adult and immature males, without the need for deconjugation of steroids in the urine. Both testosterone EIAs correlated strongly with LC-MS in adult males, but only if steroids in the urine were deconjugated by enzymatic hydrolysis prior to analysis. However, in immature males, EIA and LC-MS results did not correlate significantly. Further correlation analyses suggest this is likely due to cross-reactivity of the testosterone antibodies with other adrenal steroids such as cortisol, DHEA, and likely others, which are present at much higher concentrations relative to testosterone in immature males. Testosterone levels were significantly higher in adult compared to immature males as measured by LC-MS but not as measured by EIA. Taken together, our results suggest that the testosterone EIAs are suitable to assess gonadal activity in adult but not immature males, and only if a hydrolysis of the urine is conducted prior to analysis.

Repeatable glucocorticoid expression is associated with behavioural syndromes in males but not females in a wild primate

Behavioural syndromes are a well-established phenomenon in human and non-human animal behavioural ecology. However, the mechanisms that lead to correlations among behaviours and individual consistency in their expression at the apparent expense of behavioural plasticity remain unclear. The 'state-dependent' hypothesis posits that inter-individual variation in behaviour arises from inter-individual variation in state and that the relative stability of these states within an individual leads to consistency of behaviour. The endocrine stress response, in part mediated by glucocorticoids (GCs), is a proposed behavioural syndrome-associated state as GC levels are linked to an individual's behavioural responses to stressors. In this study, in wild Barbary macaques (Macaca sylvanus), consistent inter-individual differences were observed in both sexes for GC activity (faecal glucocorticoid, fGC concentrations), but not GC variation (coefficient of variation in fGC concentrations). The expression of the behavioural syndrome 'Excitability' (characterized by the frequencies of brief affiliation or aggressive interactions) was related to GC activity in males but not in females; more 'excitable' males had lower GC activity. There was no relationship in females between any of the behavioural syndromes and GC activity, nor in either sex with GC variation. The negative relationship between GC activity and Excitability in males provides some support for GC expression as a behavioural syndrome-generating state under the state-dependent framework. The absence of this relationship in females highlights that state-behavioural syndrome associations may not be generalizable within a species and that broader sex differences in state need to be considered for understanding the emergence and maintenance of behavioural syndromes.

Experimental field evidence that out-group threats influence within-group behavior

In social species, conspecific outsiders present various threats to groups and their members. These out-group threats are predicted to affect subsequent within-group interactions (e.g., affiliation and aggression) and individual behavior (e.g., foraging and vigilance decisions). However, experimental investigations of such consequences are rare, especially in natural conditions. We used field-based call playbacks and fecal presentations on habituated wild dwarf mongooses (Helogale parvula)-a cooperatively breeding, territorial species-to examine postinteraction responses to the simulated threat of a rival group. Dwarf mongooses invested more in grooming of groupmates, foraged closer together, and more regularly acted as sentinels (a raised guard) after encountering indicators of rival-group presence compared to control conditions. These behavioral changes likely arise from greater anxiety and, in the case of increased vigilance, the need to seek additional information about the threat. The influence of an out-group threat lasted at least 1 h but individuals of different dominance status and sex responded similarly, potentially because all group members suffer costs if a contest with rivals is lost. Our results provide field-based experimental evidence from wild animals that out-group threats can influence within-group behavior and decision making, and suggest the need for greater consideration of the lasting impacts of social conflict.

How does cognition shape social relationships?

The requirements of living in social groups, and forming and maintaining social relationships are hypothesized to be one of the major drivers behind the evolution of cognitive abilities. Most empirical studies investigating the relationships between sociality and cognition compare cognitive performance between species living in systems that differ in social complexity. In this review, we ask whether and how individuals benefit from cognitive skills in their social interactions. Cognitive abilities, such as perception, attention, learning, memory, and inhibitory control, aid in forming and maintaining social relationships. We investigate whether there is evidence that individual variation in these abilities influences individual variation in social relationships. We then consider the evolutionary consequences of the interaction between sociality and cognitive ability to address whether bi-directional relationships exist between the two, such that cognition can both shape and be shaped by social interactions and the social environment. In doing so, we suggest that social network analysis is emerging as a powerful tool that can be used to test for directional causal relationships between sociality and cognition. Overall, our review highlights the importance of investigating individual variation in cognition to understand how it shapes the patterns of social relationships.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.

Fostering of a wild, injured, juvenile by a neighbouring group: implications for rehabilitation and release of Barbary macaques confiscated from illegal trade

Illegal live trade is one of the greatest threats to endangered Barbary macaques. Since trade focuses on young and Barbary macaques show extensive alloparental care, rehabilitation and release into wild foster groups is a promising strategy to free space in sanctuaries to allow continued confiscations, improve individual welfare, minimize captive care costs, and reinforce wild populations. However, little documentation exists on Barbary macaque releases and the age at which released macaques would be accepted by foster groups is unknown. Here, I report on a wild, nearly 3-year-old Barbary macaque male that was separated from his group after serious injury from a car collision. A neighbouring group found the distressed juvenile 2 days later, approached, groomed, and affiliated with him, and accepted him into the group. He remained with the foster group for 4 months until returning to his natal group. This observation challenges concerns that only infants and young juveniles may be accepted into non-natal groups, suggesting that even older confiscated juveniles could be candidates for release. This also adds to the literature on behavioural responses to distressed and injured individuals, demonstrating the capacity of wild monkeys to exhibit affiliative behaviours even towards unfamiliar distressed conspecifics, providing a rare example of potential consolation of an unknown individual. As so little documentation currently exists on the acceptance of Barbary macaques into wild foster groups, this observation provides valuable information for developing rehabilitation and release strategies for confiscated individuals, which can be critical for continuing to fight illegal trade of this endangered species.

Network Neuroscience: A Framework for Developing Biomarkers in Psychiatry

Psychiatric disorders are disturbances of cognitive and behavioral processes mediated by the brain. Emerging evidence suggests that accurate biomarkers for psychiatric disorders might benefit from incorporating information regarding multiple brain regions and their interactions with one another, rather than considering local perturbations in brain structure and function alone. Recent advances in the field of applied mathematics generally - and network science specifically - provide a language to capture the complexity of interacting brain regions, and the application of this language to fundamental questions in neuroscience forms the emerging field of network neuroscience. This chapter provides an overview of the use and utility of network neuroscience for building biomarkers in psychiatry. The chapter begins with an overview of the theoretical frameworks and tools that encompass network neuroscience before describing applications of network neuroscience to the study of schizophrenia and major depressive disorder. With reference to work on genetic, molecular, and environmental correlates of network neuroscience features, the promises and challenges of network neuroscience for providing tools that aid in the diagnosis and the evaluation of treatment response in psychiatric disorders are discussed.

Hair cortisol and stable carbon and nitrogen isotope ratios in barbary macaques (Macaca sylvanus) from Gibraltar

RATIONALE

Prolonged exposure to the stress hormone cortisol can precipitate a catabolic state in animals resulting in a negative nitrogen balance and increased excreted nitrogen, possibly affecting stable nitrogen and carbon isotope ratios in animal tissues. Here we test the hypothesis that stress, as measured by hair cortisol, is a significant contributor to variation in δ¹⁵ N and δ¹³ C values in hair. The results of the present study have important implications for the use of stable carbon and nitrogen isotope ratios measured in animal and human tissues to make inferences regarding feeding ecology and diet.

METHODS

Samples containing roughly 10-20 hairs (approx. 4-6 cm long) were collected from 49 free ranging macaque monkeys (Macaca sylvanus) in Gibraltar. Hair samples were analyzed for stable carbon and nitrogen isotopes by continuous-flow isotope-ratio mass spectrometry. Cortisol extracted from matched hair samples was measured using gas chromatography/mass spectrometry. Cortisol and stable isotope ratios were compared statistically using nonparametric Kruskal-Wallis and Mann-Whitney U tests, as well as Spearman correlation.

RESULTS

Correlation analysis revealed that although hair δ¹⁵ N and δ¹³ C values were significantly correlated with each other, neither was correlated with cortisol concentrations. Cortisol concentrations were not correlated with age-adjusted body mass index. Age category was correlated with δ¹³ C values but not with δ¹⁵ N values.

CONCLUSIONS

The results of our study suggest that the cumulative stress experienced by these macaques under typical social and environmental conditions is not a significant contributor to variation in δ¹⁵ N and δ¹³ C values, nor does it have a significant effect on relative body mass.

Affiliation and disease risk: social networks mediate gut microbial transmission among rhesus macaques

In social animals, affiliative behaviours bring many benefits, but also costs such as disease risk. The ways in which affiliation may affect the risk of infectious agent transmission remain unclear. Moreover, studies linking variation in affiliative interactions to infectious agent incidence/diversity have speculated that disease transmission may have occurred, rather than revealing that transmission did occur. We address these gaps using the phylogenetics of commensal gut Escherichia coli to determine whether affiliative grooming and huddling social networks mediated microbial transmission among rhesus macaques. We collected behavioural and microbial data from adult macaques across a 12-week period that was split into two 6-week phases to better detect dyadic transmission. We reconstructed undirected social networks from affiliative interactions and reconstructed microbial transmission networks from the pairwise phylogenetic similarity of E. coli pulsotypes from macaques within and across adjacent sampling events. Macaque E. coli pulsotypes were more phylogenetically similar to each other than to environmental isolates, which established a premise for socially mediated transmission. Dyadic grooming and huddling frequencies strongly influenced the likelihood of E. coli transmission during the second data collection phase, but not the first. Macaques that were more central/well connected in both their grooming and huddling networks were also more central in the E. coli transmission networks. Our results confirmed that affiliative grooming and huddling behaviours mediate the transmission of gut microbes among rhesus macaques, particularly among females and high-ranking individuals. The detectability of socially mediated E. coli transmission maybe partially masked by environmental acquisition in males, or by high frequencies of interactions in captivity. Predicting the potential transmission pathways of gastrointestinal parasites and pathogens, our findings add to current knowledge of the coevolutionary relationships between affiliative behaviour and health and may be used to identify 'superspreader' individuals as potential targets for disease control strategies.

Behavioural patterns of vocal greeting production in four primate species

Social animals have evolved a range of signals to avoid aggressive and facilitate affiliative interactions. Vocal behaviour is especially important in this respect with many species, including various primates, producing acoustically distinct 'greeting calls' when two individuals approach each other. While the ultimate function of greeting calls has been explored in several species, little effort has been made to understand the mechanisms of this behaviour across species. The aim of this study was to explore how differences in individual features (individual dominance rank), dyadic relationships (dominance distance and social bond strength) and audience composition (presence of high-ranking or strongly bonded individuals in proximity), related to vocal greeting production during approaches between two individuals in the philopatric sex of four primate species: female olive baboons (Papio anubis), male chimpanzees (Pan troglodytes), female sooty mangabeys (Cercocebus atys) and female vervet monkeys (Chlorocebus pygerythrus). We found that female vervet monkeys did not produce greeting calls, while in the other three species, low-ranking individuals were more likely to call than high-ranking ones. The effects of dyadic dominance relationships differed in species-specific ways, with calling being positively associated with the rank distance between two individuals in baboons and chimpanzees, but negatively in mangabeys. In none of the tested species did we find strong evidence for an effect of dyadic affiliative relationships or audience on call production. These results likely reflect deeper evolutionary layers of species-specific peculiarities in social style. We conclude that a comparative approach to investigate vocal behaviour has the potential to not only better understand the mechanisms mediating social signal production but also to shed light on their evolutionary trajectories.

Subtypes of aggression and their relation to anxiety in Barbary macaques

Human aggression can be differentiated into reactive aggression (RA), displayed in face of a real or perceived threat and associated with high levels of anxiety, and proactive aggression (PA), displayed to achieve a certain goal and linked to lower anxiety levels. To study the origins of these aggression subtypes and their relation to anxiety, we tested if both subtypes can be distinguished in a nonhuman primate species, characterized their occurrence within the study group, and examined the link between aggression subtype and anxiety. Data were collected on 29 individuals of a semi-free ranging group of Barbary macaques (Macaca sylvanus) at Affenberg Salem, Germany, via focal animal (303 hr) and event sampling (1,222 agonistic events). Using a priori definitions, each aggressive event was classified as either reactive or proactive. We found both aggression types in our study population as well as individual differences in the proportion at which they occurred. The predominant use of one subtype of aggression was linked to the individual's dominance rank, age and sex, but not related to standard behavioral and physiological measures of anxiety. Our results suggest that reactive and proactive subtypes of aggression also exist in Barbary macaques, indicating a deeper evolutionary history of these aggression types observed in humans.

Energy balance but not competitive environment corresponds with allostatic load during development in an Old World monkey

Primates develop slowly relative to their body size, a pattern posited to result from ecological risk aversion. Little is known, however, about how energy balance contributes to allostatic load in juveniles. Using data collected over 8 consecutive months, we examined variation in energy balance (as measured by urinary C-peptide) and how energy balance, life history status, and social competition related to allostatic load (as measured by deviation from baseline fecal glucocorticoid metabolites, dfGCs) in 41 wild juvenile blue monkeys from 3 social groups. Juvenile energy balance was higher among females, when ripe fruit was more available, and when rainfall was lower. Energy balance, but not life history or competitive environments, predicted dfGC concentrations, such that juveniles generally had lower mean dfGCs when they had higher energy balance. An additional exploratory analysis of how dfGCs relate to social strategies revealed that subjects had lower dfGCs when they groomed less, and played more. Time spent grooming interacted with energy balance in predicting dfGC concentrations, so that individuals that groomed more actually had higher dfGCs when they had higher energy balance. Together these results reveal that energetic deficiencies are a true ecological risk factor in blue monkeys, and suggest that navigating the social environment via overt affiliative behavior is potentially both a stress-relieving and stress-inducing endeavor during development.

Behavioural thermoregulation via microhabitat selection of winter sleeping areas in an endangered primate: implications for habitat conservation

Strategic microhabitat selection allows animals in seasonally cold environments to reduce homeostatic energy costs, particularly overnight when thermoregulatory demands are greatest. Suitable sleeping areas may therefore represent important resources for winter survival. Knowledge of microhabitat use and potential impacts of anthropogenic habitat modification can aid species conservation through development of targeted habitat management plans. Wild, endangered Barbary macaques (Macaca sylvanus) in logged cedar-oak forest were studied to investigate (1) the hypothesis that macaques select winter sleeping areas with microhabitat characteristics that may reduce thermoregulatory costs, and, if so, (2) how to minimize damage to sleeping areas from logging. Macaques slept only in Atlas cedars (Cedrus atlantica). Consistent with predictions, macaques preferred sleeping in sheltered topography and dense vegetation, which may reduce exposure to wind, precipitation and cold, and preferred large trees that facilitate social huddling. This suggests that Barbary macaques employ strategic nocturnal microhabitat selection to reduce thermoregulatory costs and thus suitable sleeping areas may influence winter survival. To minimize negative impacts of logging on macaque sleeping areas, results suggest avoiding logging in topographical depressions and maintaining cedar densities greater than 250 ha-1 with average breast height greater than 60 cm. This study demonstrates how animal behaviour can be used to guide species-specific habitat management plans.

Greetings in male Guinea baboons and the function of rituals in complex social groups

Ritualized greetings, defined as exchanges of non-aggressive signals, are common among males living in multi-male groups and are thought to balance the trade-offs of male co-residence. While ritualized greetings are widespread in the animal kingdom, the behavioral repertoire described in the genus Papio is exceptional, as it involves potentially harmful behaviors such as genital fondling. Although greetings are one of the most striking male social interactions in baboons, their function is still disputed. We investigated the function of male-male ritualized greeting behavior in wild Guinea baboons. This species lives in multilevel societies where several 'units' comprising a primary male, females with young, and occasionally a secondary male form a 'party', and two to three parties form a gang. Adult males maintain affiliative relationships with preferred male partners whom they support in coalitions, regardless of kinship. We examined the social behavior of 24 adolescent and adult males (∼900 h focal observations) in the Niokolo-Koba National Park, Senegal, to test whether greetings reflect relationship quality or function to buffer tension. Greetings were ten times more frequent than aggression and twice as frequent as affiliation. Neither dyadic aggression nor tense context predicted greeting rate, discounting the buffering hypothesis. Greetings occurred almost exclusively between males of the same party, even when other parties were around. Within parties, spatially tolerant partners greeted more frequently but dyads did not greet due to proximity prior to the greeting. Although affiliation did not predict overall greeting rate, intense and potentially costly greetings were more likely between males with stronger affiliative relationships. Greetings in Guinea baboons appear to signal commitment among party members, test relationships among spatially tolerant partners, and accentuate relationship strength among highly affiliated males. Although ritualized baboon greetings lack the symbolic component of human rituals, they appear to serve similar functions, specifically to strengthen in-group affiliation and promote cooperation.

Non-invasive genotyping with a massively parallel sequencing panel for the detection of SNPs in HPA-axis genes

We designed a genotyping panel for the investigation of the genetic underpinnings of inter-individual differences in aggression and the physiological stress response. The panel builds on single nucleotide polymorphisms (SNPs) in genes involved in the three subsystems of the hypothalamic-pituitary-adrenal (HPA)-axis: the catecholamine, serotonin and corticoid metabolism. To promote the pipeline for use with wild animal populations, we used non-invasively collected faecal samples from a wild population of Assamese macaques (Macaca assamensis). We targeted loci of 46 previously reported SNPs in 21 candidate genes coding for elements of the HPA-axis and amplified and sequenced them using next-generation Illumina sequencing technology. We compared multiple bioinformatics pipelines for variant calling and variant effect prediction. Based on this strategy and the application of different quality thresholds, we identified up to 159 SNPs with different types of predicted functional effects among our natural study population. This study provides a massively parallel sequencing panel that will facilitate integrating large-scale SNP data into behavioural and physiological studies. Such a multi-faceted approach will promote understanding of flexibility and constraints of animal behaviour and hormone physiology.

Seasonal changes in social cohesion among males in a same-sex primate group

Male-male interactions in mixed-sex groups of social mammals are typically characterized by a mix of hostility and affiliation, as a result of inherent conflicts over mating opportunities, and the costs and benefits of social alliances, co-operative behaviors, and coalitionary defense. In species of nonhuman primates that form all-male groups, it is still unclear how the tradeoffs between the benefits of forming an all-male group and the cost of male-male competition in seeking mating opportunities with females in bisexual groups influence social cohesion in different seasons. Here, we used social network analysis to quantify the impact of reproductive seasonality on social cohesion and clique size of bachelor males residing in an all-male unit (AMU) in wild black-and-white snub-nosed monkeys (Rhinopithecus bieti). These primates are strict seasonal breeders and live in a modular social system composed of a number of one-male units (OMUs) and an associated peripheral AMU. We found that the AMU social network had a significantly lower density, centralization, clustering coefficient, and smaller clique size during the mating season compared to the non-mating period. However, aggression among AMU males during both mating and non-mating periods was low. Our results suggest that network structure topology in male same-sex social units is modulated by seasonal changes. Bachelor males engage in two types of competition to gain reproductive success: first, which is analogous to contest competition, in which bachelor males act aggressively and challenge OMU leader males in an attempt to take over an OMU; and second, which is more analogous to scramble competition, in which bachelor males avoid aggressive interactions and instead engage in sneaky copulations with fertile females. Our work adds to an understanding of the maintenance of all-male groups in species that form a multilevel society.

Rates of human-macaque interactions affect grooming behavior among urban-dwelling rhesus macaques (Macaca mulatta)

OBJECTIVES

The impact of anthropogenic environmental changes may impose strong pressures on the behavioral flexibility of free-ranging animals. Here, we examine whether rates of interactions with humans had both a direct and indirect influence on the duration and distribution of social grooming in commensal rhesus macaques (Macaca mulatta).

MATERIALS AND METHODS

Data were collected in two locations in the city of Shimla in northern India: an urban setting and a temple area. We divided these two locations in a series of similar-sized physical blocks (N = 48) with varying rates of human-macaque interactions. We conducted focal observations on three free-ranging rhesus macaque groups, one in the urban area and two in the temple area.

RESULTS

Our analysis shows that macaques engaged in shorter grooming bouts and were more vigilant while grooming in focal sessions during which they interacted with people more frequently, suggesting that humans directly affected grooming effort and vigilance behavior. Furthermore, we found that in blocks characterized by higher rates of human-macaque interactions grooming bouts were shorter, more frequently interrupted by vigilance behavior, and were less frequently reciprocated.

DISCUSSION

Our work shows that the rates of human-macaque interaction had both a direct and indirect impact on grooming behavior and that macaques flexibly modified their grooming interactions in relation to the rates of human-macaque interaction to which they were exposed. Because grooming has important social and hygienic functions in nonhuman primates, our work suggests that human presence can have important implications for animal health, social relationships and, ultimately, fitness. Our results point to the need of areas away from people even for highly adaptable species where they can engage in social interactions without human disruption.

Looking on the Bright Side of Livestock Emotions-the Potential of Their Transmission to Promote Positive Welfare

Emotions can be defined as an individual's affective reaction to an external and/or internal event that, in turn, generates a simultaneous cascade of behavioral, physiological, and cognitive changes. Those changes that can be perceived by conspecifics have the potential to also affect other's emotional states, a process labeled as "emotional contagion." Especially in the case of gregarious species, such as livestock, emotional contagion can have an impact on the whole group by, for instance, improving group coordination and strengthening social bonds. We noticed that the current trend of research on emotions in livestock, i.e., investigating affective states as a tool to assess and improve animal welfare, appears to be unbalanced. A majority of studies focuses on the individual rather than the social component of emotions. In this paper, we highlight current limitations in the latter line of research and suggest a stronger emphasis on the mechanisms of how emotions in livestock are transmitted and shared, which could serve as a promising tool to synergistically enhance the welfare of all individuals within a group.

Flexible decision-making in grooming partner choice in sooty mangabeys and chimpanzees

Living in permanent social groups forces animals to make decisions about when, how and with whom to interact, requiring decisions to be made that integrate multiple sources of information. Changing social environments can influence this decision-making process by constraining choice or altering the likelihood of a positive outcome. Here, we conceptualized grooming as a choice situation where an individual chooses one of a number of potential partners. Studying two wild populations of sympatric primate species, sooty mangabeys (Cercocebus atys atys) and western chimpanzees (Pan troglodytes verus), we tested what properties of potential partners influenced grooming decisions, including their relative value based on available alternatives and the social relationships of potential partners with bystanders who could observe the outcome of the decision. Across 1529 decision events, multiple partner attributes (e.g. dominance ranks, social relationship quality, reproductive state, partner sex) influenced choice. Individuals preferred to initiate grooming with partners of similar global rank, but this effect was driven by a bias towards partners with a high rank compared to other locally available options. Individuals also avoided grooming partners who had strong social relationships with at least one bystander. Results indicated flexible decision-making in grooming interactions in both species, based on a partner's value given the local social environment. Viewing partner choice as a value-based decision-making process allows researchers to compare how different species solve similar social problems.

Social thermoregulation as a potential mechanism linking sociality and fitness: Barbary macaques with more social partners form larger huddles

Individuals with more or stronger social bonds experience enhanced survival and reproduction in various species, though the mechanisms mediating these effects are unclear. Social thermoregulation is a common behaviour across many species which reduces cold stress exposure, body heat loss, and homeostatic energy costs, allowing greater energetic investment in growth, reproduction, and survival, with larger aggregations providing greater benefits. If more social individuals form larger thermoregulation aggregations due to having more potential partners, this would provide a direct link between sociality and fitness. We conducted the first test of this hypothesis by studying social relationships and winter sleeping huddles in wild Barbary macaques (Macaca sylvanus), wherein individuals with more social partners experience greater probability of winter survival. Precipitation and low temperature increased huddle sizes, supporting previous research that huddle size influences thermoregulation and energetics. Huddling relationships were predicted by social (grooming) relationships. Individuals with more social partners therefore formed larger huddles, suggesting reduced energy expenditure and exposure to environmental stressors than less social individuals, potentially explaining how sociality affects survival in this population. This is the first evidence that social thermoregulation may be a direct proximate mechanism by which increased sociality enhances fitness, which may be widely applicable across taxa.

Neural Mechanisms of Social Cognition in Primates

Activity in a network of areas spanning the superior temporal sulcus, dorsomedial frontal cortex, and anterior cingulate cortex is concerned with how nonhuman primates negotiate the social worlds in which they live. Central aspects of these circuits are retained in humans. Activity in these areas codes for primates' interactions with one another, their attempts to find out about one another, and their attempts to prevent others from finding out too much about themselves. Moreover, important features of the social world, such as dominance status, cooperation, and competition, modulate activity in these areas. We consider the degree to which activity in these regions is simply encoding an individual's own actions and choices or whether this activity is especially and specifically concerned with social cognition. Recent advances in comparative anatomy and computational modeling may help us to gain deeper insights into the nature and boundaries of primate social cognition.