Ethun, K. F. | Search bioRxiv

bioRxiv2026

Structure and Variation in Dam-Daughter Bonds in Captive Rhesus Macaques

Mother-daughter relationships are central to social organization in rhesus macaques, providing the foundation for kin familiarity, affiliative bias, and intergenerational rank inheritance. Understanding how these bonds are structured is therefore important for identifying the processes that contribute to matrilineal cohesion and for anticipating risks of social instability and matriline fragmentation in captive groups. We studied 141 dam-daughter dyads in large, captive groups of rhesus macaques, using generalized linear models to examine associations between demographic variables and affiliative behaviors, and a multivariate clustering approach to characterize how these behaviors combine into distinct relationship types. Our analyses identified eight distinct dam-daughter relationship types defined by combinations of three behavioral domains: grooming, spatial closeness, and agonistic support. Generalized linear models showed that demographic variables had domain-specific effects, with family size, age gaps, and dam age differentially associated with grooming, proximity, and support. These patterns were reflected in the clustering analysis, in which dyads differed not only in overall levels of behavior but also in how behaviors combined within dyads. For example, some dyads exhibited high grooming and support despite low spatial proximity, whereas others showed consistently high expression across all domains. Together, these results demonstrate that dam-daughter bonds are multidimensional and structured through the combination of multiple behavioral domains influenced by demographic and life-history factors. Because these dyads scaffold interactions among close kin, variation in dam-daughter bond structure may influence the development and stability of broader matrilineal relationships. From an applied perspective, considering multiple behavioral domains when assessing social relationships can help identify dyads that may warrant closer monitoring and inform management strategies to support matrilineal cohesion and reduce the risk of social instability in captive groups.

animal behavior and cognition↗

bioRxiv2025

Structural Effects of Low Social Status and Obesogenic Diet on Social and Emotional Neurocircuits in Female Macaques: A Longitudinal Study from Infancy to Adulthood

A substantial body of literature has demonstrated a consistent link between psychosocial stress and obesity in children, particularly in those from low socioeconomic backgrounds. Despite evidence indicating a complex interplay between stress, diet and obesity, there is a limited understanding of the specific versus potentially synergistic effects of obesity and stress on brain structural and functional development. This study investigates the developmental and long-term brain structural alterations resulting from exposure to chronic social stress due to low (subordinate -SUB-) social status and postnatal obesogenic diets. Forty-one female rhesus macaques (Dominants -DOM-, n=21; Subordinates -SUB-, n=20) were assigned to either only low-calorie diet (LCD) or to both high-calorie diet (HCD) and LCD (Choice diet) from birth through the juvenile period. After menarche, all subjects were maintained on a LCD-only diet through adulthood. Twenty-seven animals (DOM: n=13, SUB: n=14) were studied again in adulthood to investigate the long-term effects of early diet and social rank on brain structure. Cumulative Kcal consumption was measured from birth through 16 months and body weights were measured at all time points. Overall, the findings show specific effects of obesogenic diet and psychosocial stress on cortical and corticolimbic brain regions. Animals with access to the obesogenic diet had larger overall brain size (measured as intracranial volume -ICV-) and larger overall volumes of prefrontal cortex, insula, superior temporal sulcus (defined as temporo-parieto-occipital area rostral and caudal regions (TPOr and TPOc)) than those in the low-calorie diet. Most of these regional diet effects, except for the insula, were driven by general effects of the diet on brain size. The diet effects were lost when adding the adult data to the longitudinal analysis, suggesting transient effects of obesogenic diets while the animals were consuming it, but not long-term, persistent effects. These findings highlight the potential of brain rescue mechanisms that could offset lasting developmental effects of early-life obesogenic diet consumption. With respect to social rank, SUB exhibited larger volumes in brain regions related to social cognition and emotional processing than DOM animals. When the adult data was added to the longitudinal analysis, the effects of social rank were prominent in the hippocampus, superior temporal sulcus, temporo-parieto-occipital rostral region, and the temporal auditory cortices after ICV data correction, suggesting long-term, persistent and cumulative effects of these social experiences, in contrast to the transient diet effects.

neuroscience↗