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

Abstract

Chimpanzees have consistent individual differences in behavior, also referred to as personality. Similar to human personality structure, five dimensions are commonly found in chimpanzee studies that show evidence for convergent and predictive validity (Dominance, Openness, Extraversion, Agreeableness, and Reactivity/Undependability). These dimensions are to some extent heritable, indicating a genetic component that explains part of the variation in personality scores, but are also influenced by environmental factors, such as the early social rearing background of the individuals. In this study, we investigated the role of epigenetic modification of the dopamine receptor D2 gene (DRD2) as a potential mechanism underlying personality variation in 51 captive chimpanzees. We used previously collected personality trait rating data and determined levels of DRD2 CpG methylation in peripheral blood samples for these same individuals. Results showed that DRD2 methylation is most strongly associated with Extraversion, and that varying methylation levels at specific DRD2 sites are associated with changes in Extraversion in nursery-reared, but not mother-reared, individuals. These results highlight the role of dopaminergic signaling in chimpanzee personality, and indicate that environmental factors, such as social experiences early in life, can have long-lasting behavioral effects, potentially through modification of the epigenome. These findings add to the growing evidence demonstrating the importance of the experiencedependent methylome for the development of complex social traits like personality.

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

“…The effects of rearing are nonetheless modest, as evidenced by only one CpG being affected by rearing background; functional assays are needed to investigate to what extent cg26741280 methylation levels impact SLC6A4 transcription in chimpanzees. The modest effects of the atypical early-rearing conditions on methylation are in line with findings for DRD2 in chimpanzees [ 31 ] but contrast with findings in humans and require further investigation. One explanation could be that the impact of nursery rearing on chimpanzees under attentive care from humans is less traumatic and therefore only has modest effects on neural circuitry, a claim that is supported by differences in personality scores for adult chimpanzees from both background conditions.…”

“…The results do clearly support a role of serotonin methylation in chimpanzee personality regulation that differs from that of dopamine. In the same sample of chimpanzees, methylation levels of the dopamine receptor type D2 ( DRD2 ) previously showed strong associations with Extraversion and Openness, two personality dimensions that reflect a tendency to actively explore or engage with novelty [ 31 ]. While a modest link with Openness was present in our study for three out of 48 serotonergic CpG sites, no associations were found with Extraversion, while scores for Extraversion were significantly associated with methylation levels of 13 out of 16 DRD2 CpG sites.…”

“…Given that stress has been shown to impact serotonergic methylation in other species, with early life stress [ 21 ] or mild life stress [ 30 ] causing higher SLC6A4 or HTR1A methylation levels in humans or rodents, respectively, we predicted that nursery-reared individuals might have higher serotonergic methylation levels compared to mother-reared individuals. Early social rearing conditions have previously been shown to mediate the association between dopaminergic methylation patterns and Extraversion in chimpanzees, but the effects were modest [ 31 ].…”

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

“…The results do clearly support a role of serotonin methylation in chimpanzee personality regulation that differs from that of dopamine. In the same sample of chimpanzees, methylation levels of the dopamine receptor type D2 (DRD2) previously showed strong associations with Extraversion and Openness, two personality dimensions that reflect a tendency to actively explore or engage with novelty [23]. While a modest link with Openness was present in our study for three out of 48 serotonergic CpG sites, no associations were found with Extraversion, while scores on Extraversion were significantly associated with methylation levels of 13 out of 16 DRD2 CpG sites.…”

“…Given that stress has been shown to impact serotonergic methylation in other species, with early life stress [20] or mild life stress [30] causing higher SLC6A4 or HTR1A methylation levels in humans or rodents, respectively, we predicted that nursery reared individuals might have higher serotonergic methylation levels compared to mother reared individuals. Early social rearing conditions have previously been shown to mediate the association between dopaminergic methylation patterns and Extraversion in chimpanzees, but effects were modest [23].…”