Sex differences in longitudinal personality stability in chimpanzees

Abstract

Personality factors analogous to the Big Five observed in humans are present in the great apes. However, few studies have examined the long-term stability of great ape personality, particularly using factor-based personality instruments. Here, we assessed overall group, and individual-level, stability of chimpanzee personality by collecting ratings for chimpanzees (N = 50) and comparing them with ratings collected approximately 10 years previously, using the same personality scale. The overall mean scores of three of the six factors differed across the two time points. Sex differences in personality were also observed, with overall sex differences found for three traits, and males and females showing different trajectories for two further traits over the 10 year period. Regardless of sex, rank-order stability analysis revealed strong stability for dominance; individuals who were dominant at the first time point were also dominant 10 years later. The other personality factors exhibited poor to moderate rank-order stability, indicating that individuals were variable in their rank-position consistency over time. As many studies assessing chimpanzee cognition rely on personality data collected several years prior to testing, these data highlight the importance of collecting current personality data when correlating them with cognitive performance.

Chimpanzee Extraversion scores vary with epigenetic modification of dopamine receptor gene D2 (DRD2) and early rearing conditions

“…It is thus possible that methylation levels do not fully represent the methylome profile associated with the personality profile at the time of sampling. However, we do not expect this to have a major impact on the results as Extraversion and Openness are two personality traits with good stability across time in chimpanzees (Rawlings et al, 2020), and the mean difference between the dates of personality rating and blood sample collection was relatively low (Mean = 2.11 years, SD= 3.96) for a longlived species like chimpanzees. Our study sample was also limited in age range for properly estimating methylation effects of dopamine on personality across the chimpanzee lifespan.…”

The Role of Serotonergic Gene Methylation in Regulating Anxiety-Related Personality Traits in Chimpanzees

“…Five out of six dimensions show strong evidence for convergent and predictive validity, meaning they are consistent among raters and among studies, and show expected correlations with independently collected quantitative behavioral observations [ 28 , 32 , 33 , 34 ]. Three out of six dimensions (Agreeableness, Dominance, Reactivity/Undependability) showed significant stability up to ten years between ratings, with Dominance showing the strongest stability [ 35 ]. Given that the personality dimension “Methodical” tended to differ between studies, and showed poor construct validity and low stability over time, we excluded it here.…”

“…Given that the personality dimension “Methodical” tended to differ between studies, and showed poor construct validity and low stability over time, we excluded it here. Construct validity of the personality questionnaire was carried out for individuals of all age ranges included in this study [ 28 , 35 ].…”

Leveling the playing field in studying cumulative cultural evolution: Conceptual and methodological advances in nonhuman animal research.

“…Whether animals attempt and persist at tasks, for example, can decline with age (Barbary macaques, Macaca sylvanus ; Rathke & Fischer, 2020), whereas perseveration with known solutions or strategies can increase (rhesus macaques; Lai et al, 1995; e.g., on aging and cognitive decline in other species, see Chapagain et al [2020] for dogs, Kapellusch et al [2018] for rats, and Kwapis et al [2020] for mice). Openness, linked with cognitive performance, also changes over the chimpanzee life span—with males in particular decreasing over adulthood (Rawlings et al, 2020). Candidate CCE behaviors such as nut-cracking are cognitively demanding and can take years to master, and if aging populations are showing cognitive decline, these factors will have significant implications for studies of animal learning.…”

“…At the individual level, factors such as personality, dominance status, prior testing experience, social status, and rearing history are important causes of selection bias (Altschul et al, 2017; Brosnan et al, 2015; Herrelko et al, 2012; Hopper et al, 2014; Morton et al, 2013; Rawlings et al, 2020). Much of primate behavioral research is based on voluntary participation, for good reason, but this also means that individuals who enjoy testing and/or are high ranking enough are most likely to participate, and indeed, they may act as trained demonstrators—which affects subsequent learning of behaviors in groups (Kendal et al, 2015; Vale et al, 2021; Watson et al, 2017).…”