Tenure in current captive setting and age predict personality changes in adult pigtailed macaques

Abstract

Personality change in nonhuman primates is a topic that warrants more research attention. Many studies focus on intraindividual repeatability, but few note population-wide trends in personality change. In part, this results from the large sample size that is required to detect such trends. In the present study, we measured personality in a large sample (N = 293) of adult, mother-reared pigtailed macaques, Macaca nemestrinam, over a period of 3 years. We looked at four personality components (sociability towards humans, cautiousness, aggressiveness and fearfulness) derived from behavioural observations at two to four time points per subject. We found these components to have repeatabilities similar to those reported elsewhere in the literature. We then analysed population-wide changes in personality components over time using a linear mixed effects model with three predictors: entry age at the current primate facility, tenure at the primate facility at the time of the first personality test and time elapsed since the first personality test. We found that adult personality changed with life experiences (here, tenure at the facility where tested) and age. Throughout adulthood, pigtailed macaques became less cautious and more aggressive. At the same time, subjects became less cautious and more sociable with increasing time in individual caging at the current primate research facility. We also found that individuals differed significantly in their personality consistency. Other researchers may benefit by applying similar methodology to that described here as they extrapolate about personality measures over time.

Developing individual differences in primate behavior: the role of genes, environment, and their interplay

“…Migration is typically accompanied by increases in mortality or injury rates, decreases in access to resources, and social costs, i.e., the loss of social ties or rank (Dittus 1979;Weiß et al 2016). Following migration, male rhesus macaques show more fearful and less physically aggressive behavior than before (von Borell et al 2016), which is consistent with findings from captive pigtailed macaques, where individuals that are new to a facility are more cautious (Sussman et al 2014). Migration may also trigger rank-order changes in behavior, possibly reflecting different reactions or strategies following migration.…”

Dominance rank causally affects personality and glucocorticoid regulation in female rhesus macaques

“…Our results show that dominance rank is a major driver of several dimensions of personality, especially boldness and social approachability, although some intra-individual stability of boldness and anxiousness is detectable across groups and ranks. After controlling for rank, we also found that age predicted behavioral tendency, which may reflect overall age-associated declines in activity level (Moscrip et al, 2000) or more specific behavioral fluctuations that have been reported to occur with age in pigtail macaques ( Macaca nemestrina ) (Sussman et al, 2014). Together, these findings suggest that some behavioral tendencies in female rhesus macaques are more stable and trait-like (e.g.…”

A human model for primate personality

“…These findings came from studies in settings as diverse as zoos and sanctuaries, laboratories and the field, and in studies that used ratings to assess personality [58][59][60][61][62][63][64][65] and studies that used behavioural observations and tests [66][67][68][69]. In addition, one of these studies [58] found that among female rhesus monkeys who gave birth for the first time between assessments, there were marked declines in the stabilities of the confident and sociable domains, but not for the excitable domain.…”

“…[77]) and behavioural tests and observations (e.g. [68]). However, it appears that only two studies tested whether the rate of personality change in primates matches the rate found in humans.…”