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In several species, rank predicts access to food, and subordinates may need specific behavioural strategies to get a share of resources. This may be especially important in despotic species, where resources are strongly biased in favour of dominants and subordinates may more strongly rely on specific tactics to maximize food intake. Here, we compared three macaque species with an experimental set-up reproducing feeding competition contest. Following our predictions, more tolerant species mostly retrieved food in the presence of others and were less dependent on specific tactics. Contrarily, subordinates in more despotic species more likely collected food (1) when dominants could not see food or (2) were attacking others, (3) while “dissimulating”, or (4) “storing food”. Our study reveals that dominance styles reliably predict the probability of using specific food retrieval tactics and provides important insights on the social conditions that might have led to the emergence of tactical deception.

Primates live in complex social systems with social structures ranging from more to less despotic. In less despotic species, dominance might impose fewer constraints on social choices, tolerance is greater than in despotic species and subordinates may have little need to include novel food items in the diet (i.e. neophilia), as contest food competition is lower and resources more equally distributed across group members. Here, we used macaques as a model to assess whether different dominance styles predict differences in neophilia and social tolerance over food. We provided familiar and novel food to 4 groups of wild macaques (N = 131) with different dominance styles ( Macaca fuscata , M. fascicularis , M. sylvanus , M. maura ). Our study revealed inter- and intra-specific differences in individuals’ access to food, which only partially reflected the dominance styles of the study subjects. Contrary to our prediction, social tolerance over food was higher in more despotic species than in less despotic species. Individuals with a higher dominance rank and being better socially integrated (i.e. higher Eigenvector centrality) were more likely to retrieve food in all species, regardless of their dominance style. Partially in line with our predictions, less integrated individuals more likely overcame neophobia (as compared to more integrated ones), but only in species with more tolerance over food. Our study suggests that individual characteristics (e.g. social integration or personality) other than dominance rank may have a stronger effect on an individual’s access to resources.

Gaze sensitivity allows us to interpret the visual perspective of others, inferring their intentions and attentional states. In order to clarify the evolutionary history of this ability, we assessed the response of free-ranging Japanese macaques ( Macaca fuscata ) to human gaze in three contexts: threat (Experiment 1), cooperation (Experiment 2), and competition (Experiment 3). Subjects interpreted the direct gaze of an approaching human as a sign of threat, showing a greater flight initiation distance and more threats towards the human in this condition than when the human gazed in another direction. Subjects also adapted their behavior to the attentional cues of a human who gave them food, by for example moving into his visual field. However, the macaques did not seem to take the visual perspective of a human competing with them over food, as they failed to first retrieve the food that was not visible to the human (i.e., located behind an opaque barrier). Our results support the idea that Japanese macaques can respond to a human’s gaze flexibly depending on the context. Moreover, they highlight the importance of studying animal behavior across different species and contexts to better understand the selective pressures that might have led to its evolution.

This book is a detailed study of monkey parks in Japan. It describes how the parks manage free-ranging macaque troops for touristic display and examines the various problems that arise, as well as proposals for park reform.

Quantification of behaviors in macaques provides crucial support for various scientific disciplines, including pharmacology, neuroscience, and ethology. Despite recent advancements in the analysis of macaque behavior, research on multi-label behavior detection in socially housed macaques, including consideration of interactions among them, remains scarce. Given the lack of relevant approaches and datasets, we developed the Behavior-Aware Relation Network (BARN) for multi-label behavior detection of socially housed macaques. Our approach models the relationship of behavioral similarity between macaques, guided by a behavior-aware module and novel behavior classifier, which is suitable for multi-label classification. We also constructed a behavior dataset of rhesus macaques using ordinary RGB cameras mounted outside their cages. The dataset included 65 913 labels for 19 behaviors and 60 367 proposals, including identities and locations of the macaques. Experimental results showed that BARN significantly improved the baseline SlowFast network and outperformed existing relation networks. In conclusion, we successfully achieved multilabel behavior detection of socially housed macaques with both economic efficiency and high accuracy.

The macaque genus includes 25 species with diverse social systems, ranging from low to high social tolerance grades. Such interspecific behavioral variability provides a unique model to tackle the evolutionary foundation of primate social brain. Yet, the neuroanatomical correlates of these social tolerance grades remain unknown. To address this question, we expressed social tolerance grades within a novel cognitive framework and analyzed post-mortem structural scans from 12 macaque species. Our results show that amygdala volume is a subcortical predictor of macaques’ social tolerance, with high tolerance species exhibiting larger amygdala than low tolerance ones. We further investigated the developmental trajectory of amygdala across social grades and found that intolerant species showed a gradual increase in relative amygdala volume across the lifespan. Unexpectedly, tolerant species exhibited a decrease in relative amygdala volume across the lifespan, contrasting with the age-related increase observed in intolerant species—a developmental pattern previously undescribed in primates. Taken together, these findings provide valuable insights into the cognitive, neuroanatomical, and evolutionary basis of primates’ social behaviors. Macaque monkeys live under a variety of social regimes. Some species flourish within highly structured, hierarchical societies, while others navigate more tolerant yet less predictable social networks. Primatologists have categorised these social differences, including how often reconciliation occurs after conflicts, into four levels of social tolerance. However, the neuronal mechanisms underlying these social variations remain poorly understood. Closely related species offer a natural laboratory for studying the social brain in primates. To investigate how neural networks may have evolved in response to differing social challenges, Silvère et al. analysed 43 brain scans from 12 macaque species. All data were gathered from animals that had died of natural or accidental causes The scans showed that the relative size of a species’ amygdala – a brain region involved in emotional responses, decision-making, and memory – correlates with its level of social tolerance. For example, low-tolerance species are born with a smaller amygdala, which grows larger with age. Conversely, in more socially tolerant species, the amygdala decreases in size as they age, contrasting with findings in other primates, including humans. These findings imply that living in a more tolerant social environment could impose greater cognitive demands on the brain, with the amygdala possibly playing a part in complex social cognition. In contrast, the volume of a brain region called the hippocampus revealed more variable differences across social grades among macaques, with a more significant effect observed only in individuals aged between 13 and 18 years. Additionally, differences in hippocampal volume also varied among monkeys living in different areas, supporting the idea that certain regions contribute to social cognitive processes in tolerant species, particularly during developmental phases linked to social maturation. Exploring natural variation in brain evolution and function opens new avenues for primate neuroscience. A more extensive comparative analysis across all living primate species could further clarify evolutionary pathways. Moreover, identifying neural networks that are either evolutionarily conserved or highly variable may help shape new research directions aimed at understanding the biological basis of neurodivergence.

The neural mechanisms mediating sensory-guided decision-making have received considerable attention, but animals often pursue behaviors for which there is currently no sensory evidence. Such behaviors are guided by internal representations of choice values that have to be maintained even when these choices are unavailable. We investigated how four macaque monkeys maintained representations of the value of counterfactual choices—choices that could not be taken at the current moment but which could be taken in the future. Using functional magnetic resonance imaging, we found two different patterns of activity co-varying with values of counterfactual choices in a circuit spanning the hippocampus, the anterior lateral prefrontal cortex and the anterior cingulate cortex. Anterior cingulate cortex activity also reflected whether the internal value representations would be translated into actual behavioral change. To establish the causal importance of the anterior cingulate cortex for this translation process, we used a novel technique, transcranial focused ultrasound stimulation, to reversibly disrupt anterior cingulate cortex activity.Fouragnan et al. used neuroimaging and ultrasound neuromodution in non-human primates to demonstrate the causal role of the anterior cingulate cortex in translating counterfactual values in future choices.

Growing contacts between humans and nonhuman primates at interface zones bring forth the need to better understand the efficiency and implications of synanthropic primates population management strategies. In this context, the expanding use of fertility control contrasts with the limited documentation of its potential consequences for primate behavior and social dynamics. Unlike other methods, tubectomy preserves the ovarian functions involved in sexual motivation of female macaques. However, sexual behaviors and aggression could intensify due to a higher proportion of cycling females within the group. In this study, we assessed whether tubectomy modifies the sociosexual interactions of female long-tailed macaques ( Macaca fascicularis ) in a primate-tourism site in Bali, Indonesia. Using focal sampling over a three-year period ( N = 56 females), we investigated changes in (a) female sociosexual activities (i.e., sexual and grooming interactions with males), and (b) female intrasexual aggression (i.e., female-female agonistic interactions). Using causal inference statistics, we found that (a) compared with intact females, sterilized females were more sexually receptive and attractive, and they received longer grooming bouts from male partners. Surprisingly, (b) tubectomy was associated with decreased intrasexual aggression among females, as sterilized females received aggression from fewer female opponents compared with intact females. This study showed that, at least in the short term, tubectomy modifies the sociosexual interactions, while not heightening female aggression. These findings may inform management decisions that maximize social stability and welfare of synanthropic populations. However, the long-term implications of female sterility for social dynamics warrant further investigation.

Primates form strong social bonds and depend on social relationships and networks that provide shared resources and protection critical for survival. Social deficits such as those present in autism spectrum disorder (ASD) and other psychiatric disorders hinder the individual's functioning in communities. Given that early diagnosis and intervention can improve outcomes and trajectories of ASD, there is a great need for tools to identify early markers for screening/diagnosis, and for translational animal models to uncover biological mechanisms and develop treatments. One of the most widely used screening tools for ASD in children is the Social Responsiveness Scale (SRS), a quantitative measure used to identify individuals with atypical social behaviors. The SRS has been adapted for use in adult rhesus monkeys (Macaca mulatta)-a species very close to humans in terms of social behavior, brain anatomy/connectivity and development-but has not yet been validated or adapted for a necessary downward extension to younger ages matching those for ASD diagnosis in children. The goal of the present study was to adapt and validate the adult macaque SRS (mSRS) in juvenile macaques with age equivalent to mid-childhood in humans. Expert primate coders modified the mSRS to adapt it to rate atypical social behaviors in juvenile macaques living in complex social groups at the Yerkes National Primate Research Center. Construct and face validity of this juvenile mSRS (jmSRS) was determined based on well-established and operationalized measures of social and non-social behaviors in this species using traditional behavioral observations. We found that the jmSRS identifies variability in social responsiveness of juvenile rhesus monkeys and shows strong construct/predictive validity, as well as sensitivity to detect atypical social behaviors in young male and female macaques across social status. Thus, the jmSRS provides a promising tool for translational research on macaque models of children social disorders.