A multicenter study was undertaken to generate new weight-for-age growth standards to monitor the growth of infant rhesus and pigtail macaques in research breeding colonies. Previously, single institutions have developed reference growth curves, under the assumption of linear growth, for infants raised in certain settings with a limited scope of benefit to outside institutions. Weight and health records from seven research institutions across the USA were used to build models of body weight by age. Linear and Box-Cox Power Exponential (BCPE) distribution models, which have been adopted from the World Health Organization's methods, were compared to find the best fit of the models. Resultant weight percentiles and growth velocity charts were provided from the best-fit model ranked by generalized Akaike's information criterion. Multiparameter models with the BCPE distribution fit the data better than linear models with normal distributions. The assumption that infant macaque growth is linear was challenged by our findings; growth rates appear to change over the first year of life for infant macaques. Growth standards were integrated into centile charts and a computer application in MS Excel to provide user-friendly weight-for-age percentile charts to access and analyze macaque growth data. The new growth standards provide a unified reference that best represents normal physiological growth for all infant rhesus and pigtail macaques from birth through the first year of life. These standards offer guidance on expected growth trajectories and serve as a benchmark for assessing the healthy development of macaque infants across research breeding colonies.

Social dominance hierarchies are embedded within multivariate and multiscale behavioural processes, where patterns of individual interactions form the basis of social bonds and give rise to higher-order emergent social properties. While the links between current dominance rank and social network position have been broadly established, less is known about the social precursors and consequences of rank reversals or the scale at which these processes are quantifiable. Here we considered how longitudinal hierarchy dynamics relate to an individual's unilayer and multilayer centrality in a large group of captive rhesus macaques. We considered two interrelated ideas: first, which social variables predict individuals' subsequent ascension or descension in the dominance hierarchy; second, the influence of individual rank changes on their subsequent social centrality. Prior to ascending the hierarchy, we found that individuals were less socially central. This decreased centrality was indicated through lower unilayer subordination-signalling instrength, contact sitting strength, subordination-signalling authority scores, aggression authority scores, multilayer PageRank versatility (centrality across and within layers) and multilayer consensus rank. Positive rank change, however, was a poor predictor of subsequent network centrality. Prior to descending the hierarchy, individuals were characterized by lower grooming degree and subordination-signalling authority scores. Negative rank change was, however, a strong predictor of subsequent social position: individuals had lower grooming degree, lower aggression authority scores and lower multilayer PageRank versatility. Overall, these findings suggest that rank change, regardless of direction, has social precursors and consequences in temporally adjacent 90-day periods. These dynamics can be captured at the local, individual scale (unilayer) and as emergent properties (authority scores, multilayer networks). Our findings highlight the individual and combined value of unilayer and multilayer approaches to better understand the dynamics of social structure. (c) 2026 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

Social relationships profoundly impact health in social species. Much of what we know regarding the impact of affiliative social relationships on health in nonhuman primates (NHPs) has focused on the structure of connections or the quality of relationships. These relationships are often quantified by comparing different types of affiliative behaviors (e.g., contact sitting, grooming, proximity) or pooling affiliative behaviors into an overall measure of affiliation. However, it is unclear how the breadth of affiliative behaviors (e.g., how many different types or which ones) a dyad engages in impact health and fitness outcomes. We used a novel social network approach to quantify the breadth of affiliative relationships based on two behaviors: grooming and sitting in contact. Dyadic relationships were filtered into separate networks depending on whether the pair engaged in multiple affiliative behaviors (multiplex networks) or just one (uniplex networks). Typically, in social network analysis, the edges in the network represent the presence of a single behavior (e.g., grooming) regardless of the presence or absence of other behaviors (e.g., contact sitting, proximity). Therefore, to validate this method, we first compared the overall structure of the standard network for each affiliative behavior: all grooming interactions regardless of contact sitting, and all contact sitting interactions regardless of grooming. We then similarly compared the structure of our filtered multiplex vs. uniplex networks. Results indicated that multiplex networks were more modular, reciprocal, and kin-based while connections in uniplex networks were more strongly associated with social status. These differences were not replicated when comparing networks based on a single behavior alone (i.e., all grooming networks vs. all contact sitting networks). Next, we evaluated whether individual network position in multiplex vs. uniplex (novel approach) or grooming vs. contact sitting (traditional approach) networks differentially impact inflammatory biomarkers in a commonly studied non-human primate model system, the rhesus macaque (Macaca mulatta). Being well connected in multiplex networks (networks where individuals both contact sat and groomed) was associated with lower inflammation (IL-6, TNF-alpha). In contrast, being well connected in uniplex grooming networks (dyad engaged only in grooming and not in contact sitting) was associated with greater inflammation. Altogether, these results suggest that multiplex relationships may function as supportive relationships (e.g., those between kin or strong bonds) that promote health. In contrast, the function of uniplex grooming relationships may be more transactional (e.g., based on social tolerance or social status) and may incur physiological costs. This complexity is important to consider for understanding the mechanisms underlying the association of social relationships on human and animal health.

Psychological duress can emerge from the perceived lack of predictability such that, in captive circumstances, reliable signals for aversive events can afford animals with the opportunity to behaviorally and physiologically prepare. Does a reliable and unique signal cue for an aversive management event reduce reactivity to management events that share unreliable cues? We recorded animal responses to management events near, or involving, outdoor-housed rhesus macaques (Macaca mulatta) in two large mixed-sex groups, with experimental periods that introduced a signal coupled to catch events. Management events varied in the severity and magnitude of animal responses. Our results validated that catches were more disruptive than management events that indirectly involved animal subjects, yet were comparable to management events involving direct interactions. Signal use reduced aversive responses to more routine management events that shared unreliable cues with catches. Due to the abundance of these routine events, we assert that the value of change with the implementation of the signal provided a detectable improvement across multiple measures of disruption.

In animal social groups, the extent to which individuals consistently win agonistic interactions and their ability to monopolize resources represent 2 core aspects of their competitive regime. However, whether these two aspects are closely correlated within groups has rarely been studied. Here, we tested the hypothesis that hierarchy steepness, which is generally used to represent power differentials between group members, predicts the variation in the distribution of fitness-related benefits (i.e. fecundity, infant survival, mating success, and feeding success) in relation to individual dominance ranks. We tested this hypothesis in primate groups using comparative phylogenetic meta-analytical techniques. Specifically, we reviewed published and unpublished studies to extract data on individual dominance ranks, their access to fitness-related benefits, and hierarchy steepness. We collected and included in our analysis a total of 153 data points, representing 27 species (including 2 chimpanzee sub-species). From these, we used 4 common methods to measure individual dominance ranks and hierarchy steepness, i.e. Dij-based normalized David's scores, randomized Elo-ratings, and David's scores and Elo-ratings estimated in Bayesian frameworks. We found that hierarchy steepness had no effect on the strength of the relationship between dominance rank and access to fitness-related benefits. Our results suggest that hierarchy steepness does not reflect between-group variation in the extent to which individual dominance affects the acquisition of fitness-related benefits in primates. Although the ability to win agonistic encounters is essential, we speculate that other behavioral strategies adopted by individuals may play crucial roles in resource acquisition in animal competitive regimes. In social animals, group members compete to attain dominant positions. Dominant individuals are expected to have better access to key resources, like food or mating. In our study, we show that the strength of the dominance hierarchy does not affect the distribution of key resources in primates. The distribution of social bonds and agonistic support between group members may weaken the effect of dominance hierarchy on how key resources are accessed by dominants and subordinates.

ABSTRACT Sooty mangabeys (SMs) are natural hosts of simian immunodeficiency virus (SIV) and do not progress to AIDS despite high viral replication. The main factors involved in the benign nature of this infection are (i) low level of immune activation, (ii) relative preservation of specific CD4+ T-cell subsets from direct virus infection, and (iii) absence of microbial translocation from the gut to the systemic circulation. To determine the impact of SIV infection on underlying cause of death, we retrospectively analyzed data from 307 SMs (219 SIV infected and 88 uninfected) housed at the Emory Primate Center that have died between 1986 and 2022. Interestingly, we found that SIV-infected SMs live ~4 years longer than SIV-uninfected SMs, although this result is hard to interpret due to differences in how animals were housed and assigned to specific experimental studies. While the causes of death were not different between SIV-infected and uninfected SMs that died before age 15 (i.e., adult), we found significant differences in the relative frequency of specific causes of death in the elderly population (≥15 years old). Specifically, we observed that SIV-infected SMs were more likely to die from infections but less likely to die from cardiovascular disease (and diabetes in female animals) as compared to uninfected SMs. While confirming the non-pathogenic nature of SIV infection in SMs, these data reveal, for the first time, a qualitative impact of SIV infection on the host physiology that induces a significant change in the mortality pattern in these natural SIV hosts. IMPORTANCE In this study, we demonstrate, for the first time, that the natural, non-pathogenic SIV infection of the African monkey SM has a clinical impact which is revealed in terms of main causes of mortality, which are significantly different in the infected animals as compared to the uninfected ones. Indeed, SIV-infected SMs are at higher risk of dying of infectious diseases but appear to be somewhat protected from cardiovascular causes of death. The identification of a specific pattern of mortality associated with the infection suggests that the host-pathogen interaction between SIV and the SM immune system, while non-pathogenic in nature, has a detectable impact on the overall health status of the animals.

Keystone individuals are expected to disproportionately contribute to group stability. For instance, rhesus macaques (Macaca mulatta) who police conflict contribute towards stability. Not all individuals' motivations align with mechanisms of group stability. In wild systems, males typically disperse at maturity and attempt to ascend via contest competition. In a captive system, dispersal is not naturally enabled - individuals attempt to ascend in their natal groups, which can be enabled by matrilineal kin potentially destabilizing group dynamics. We relocated select high-ranking natal males from five groups and assessed group stability before and after. We quantified hierarchical metrics at the individual and group level. After removal, we found significantly higher aggression against the established hierarchy (reversals), indicative of opportunistic attempts to change the hierarchy. Mixed-sex social signaling became more hierarchical, but the strength of this effect varied. Stable structure was not uniformly reached across the groups and alpha males did not all benefit. Indiscriminate natal male removal is an unreliable solution to group instability. Careful assessment of how natal males are embedded within their group is necessary to balance individual and group welfare.

Dominance hierarchies are a key feature in the dynamics of animal social groups, playing a crucial role in fostering group stability. Despite often being viewed as static, persistent linear structures, hierarchies are fundamentally dynamic and can change over time due to ecological conditions, demographic changes and ontogenetic development. There are numerous methods used to construct hierarchies and quantify individual dominance rank, but methods to capture the dynamics of a hierarchy across time have only recently been developed. As such, relatively little is known about the longitudinal hierarchy dynamics in many social species, including nonhuman primates, and the timescale at which these hierarchy dynamics play out. Here we consider the longitudinal hierarchy dynamics across a 4-year period in a large group of rhesus macaques, Macaca mulatta. We investigated group and individual level predictors of active rank dynamics, or dynamics that arise from rank reversals. We found that, despite rhesus macaques being considered to have relatively stable hierarchies, there was significant active rank mobility in both males and females, even in the face of limited resource competition. Female rank change was not solely driven by matrilineal structure or demographic processes as females also opportunistically ascended in rank. Furthermore, we found strong links between rank certainty and hierarchy dynamics with periods of high hierarchy instability associated with low mean dominance certainty. Lastly, we found limited evidence of associations between periods of high active rank dynamics and social global network structure. This suggests more localized dynamics during hierarchy instability are at play rather than widescale network reorganization. Together, these results stress the importance of considering social context in rank dynamics, illustrate the dynamic nature of macaque dominance rank and further highlight the opportunistic nature of the species. (c) 2024 The Authors. Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

Social network position in non-human primates has far-reaching fitness consequences. Critically, social networks are both heterogeneous and dynamic, meaning an individual's current network position is likely to change due to both intrinsic and extrinsic factors. However, our understanding of the drivers of changes in social network position is largely confined to opportunistic studies. Experimental research on the consequences of in situ, controlled network perturbations is limited. Here we conducted a food-based experiment in rhesus macaques to assess whether allowing an individual the ability to provide high-quality food to her group changed her social behavioural relationships. We considered both her social network position across five behavioural networks, as well as her dominance and kin interactions. We found that gaining control over a preferential food resource had far-reaching social consequences. There was an increase in both submission and aggression centrality and changes in the socio-demographic characteristics of her agonistic interaction partners. Further, we found that her grooming balance shifted in her favour as she received more grooming than she gave. Together, these results provide a novel, preliminary insight into how in situ, experimental manipulations can modify social network position and point to broader network-level shifts in both social capital and social power.

Comparative studies reliant on single personality surveys to rate wild primates are scarce yet remain critical for developing a holistic comparative understanding of personality. Differences in survey design, item exclusion, and factor selection impede cross-study comparisons. To address these challenges, we used consistently collected data to assess personality trait structures in wild rhesus (Macaca mulatta), bonnet (M. radiata), and long-tailed (M. fascicularis) macaques that varied in their degree of phylogenetic closeness, species-typical social styles, and anthropogenic exposure in urban or urban-rural environments. We administered 51-item personality surveys to familiar raters, and, after reliability and structure screenings, isolated 4-5 factor solutions among the species. Four consistent factors emerged: Confident, Sociable, Active, and Irritable/Equable. This latter factor had differential expression across species. Item composition of the Irritable/Equable factor was consistent with their anticipated differences in social styles, but confounded by cross-site anthropogenic variation. We also administered a 43-item survey confined to human-primate situations which paralleled our findings of social style variation, while also exhibiting variation that aligned with population differences in human density. Our findings indicate that macaque personality trait structures may be emergent outcomes of evolutionary and/or socioecological processes, but further research is needed to parse these processes' relative contributions.

Social network analysis (SNA) is a powerful, quantitative tool to measure animals' direct and indirect social connectedness in the context of social groups. However, the extent to which behavioural sampling methods influence SNA metrics remains unclear. To fill this gap, here we compare network indices of grooming, huddling, and aggression calculated from data collected from three macaque species through two sampling methods: focal animal sampling (FAS) and all-occurrences behaviour sampling (ABS). We found that measures of direct connectedness (degree centrality, and network density) were correlated between FAS and ABS for all social behaviours. Eigenvector and betweenness centralities were correlated for grooming and aggression networks across all species. By contrast, for huddling, we found a correlation only for betweenness centrality while eigenvector centralities were correlated only for the tolerant bonnet macaque but not so for the despotic rhesus macaque. Grooming and huddling network modularity and centralization were correlated between FAS and ABS for all but three of the eight groups. By contrast, for aggression network, we found a correlation for network centralization but not modularity between the sampling methodologies. We discuss how our findings provide researchers with new guidelines regarding choosing the appropriate sampling method to estimate social network metrics.

Relatedness and kinship structure in matrilines are a potential source of social stability. The current study aimed to analyze the extant pedigrees of 6 living matrilines in different field cages to assess rates of cross-generational inbreeding and loss of genetic variation over time. All 6 matrilines showed increasing levels of inbreeding over generation time, although the rates of increase were different. The female-to-male-adult sex ratio was correlated with average matriline inbreeding levels, while the number of adult males was positively correlated with average matriline genetic diversity. Over five times more paternal half-sibs than maternal half-sibs were present because paternity had been restricted to a few males yearly. Therefore, the relatedness through the paternal lines was over five times greater than that of the maternal lines. Overall, each matriline lost low to moderate levels of genetic variation with time. The current rates of gene flow between field cages by cross-fostered infants have not stopped inbreeding within these matrilines or loss of diversity due to genetic drift. This situation probably developed because translocated animals, especially males, may not breed successfully. Only 4 of the 22 translocated individuals, all females, eventually reproduced, resulting in 13 offspring and generating an overall breeding success of 0.59 across all 6 study matrilines. However, even this low rate of reproduction by the translocated animals reduced inbreeding and kinship among matrilines and increased genetic heterogeneity in the matrilines. Based on this study, we propose several colony management strategies, including equalizing adult sex ratios to increase the effective population size in the field cages, increasing the number of cross-fostered infants, and relying more on multigenerational pedigree data to aid the alignment of genetic and behavioral management techniques.

ABSTRACT There is significant variability in the extent to which individuals from group-living species participate in intergroup competition (IGC) over resources. Such variability may be particularly robust in human-impacted environments, wherein anthropogenic resources may strongly impact intergroup overlap and competition. Examining the socio-ecological causal factors driving these differences can shed new lights on animals’ costs-benefits trade-offs driving engagement in such interactions. Here we use (peri)urban-dwelling rhesus macaques ( Macaca mulatta ) as model-systems to examine how individual differences in socio-ecological characteristics (i.e., animals’ sex, rank, and affiliative connections) may influence propensities to participate in IGC in anthropogenic environments. We found that participation was strongly influenced by individuals’ affiliative connections. Interestingly, monkeys with more coalitionary support partners had higher IGC participation, but this was more pronounced for individuals that are more peripheral in their proximity and multilayer affiliative networks, compared to more socially central individuals. Moreover, males and low-ranking individuals were more likely to participate in IGC. Our findings suggest that differential access to socio-ecological resources likely drives IGC participation. The evaluation of such inter-individual differences in socio-ecological flexibility and decision-making in dynamic environments is critical for future research related to the links between behavioural ecology, health outcomes, and human-wildlife co-existence in anthropogenic landscapes.

Herein we provide a review of the importance of social relationships on health and welfare of nonhuman primates. Social relationships are a key component of life for most primates. Sociality, however, comes with costs and benefits to health and welfare. When examining these benefits and costs we can look at two main types of primate relationships: dominance relationships/social status and affiliative relationships/social bonds. Over millions of years of evolution, many primate species experienced selection for larger brains (relative to body size) and living in cohesive social groups, which has resulted in a social life that is fundamentally linked to their welfare. These two evolutionary characteristics lead to complexity in both the dominance relationships and social bonds that develop in many primate societies. Individual dominance rank may be associated with differential risk of injury, exposure to stress, and other welfare-related outcomes because dominance relationships govern competitive interactions over access to resources and mating opportunities. Similarly, the affiliative social bonds between primates can also impact welfare because such interactions offer a way to cope with social stress yet increase risk of disease transmission via contact. Zoos, sanctuaries, research facilities, and other institutions that house nonhuman primates in captivity must take into consideration such social relationships in their management strategies and procedures to promote good welfare. Here we discuss these social relationships in relation to individual health, fitness, and well-being.