Abstract
To investigate the genetic basis of social behavior we searched for polymorphisms of the mu-opioid receptor gene (OPRM1) in chimpanzees. The non-synonymous polymorphism of the gene of the extracellular region has been reported to affect social behavior in humans and rhesus macaques. We surveyed a corresponding region in 135 chimpanzees kept in Japanese Zoos and found a 3 base pair indel (L: insertion, S: deletion) coding aspartic acid. L and S allele frequencies were 0.611 and 0.389, respectively. To survey personality three caretakers familiar with the chimpanzee answered 54 questions on a scale of 1-7. The 54 questions were categorized into six factors: Dominance, Extraversion, Conscientiousness, Agreeableness, Neuroticism, and Openness. To examine the association between genotype and personality we ran linear regression models with each personality component as the dependent variable and genotype and sex as independent variables. We first ran a basic model looking at the main effect of genotype. We then added sex as a main effect and the sex × genotype interaction. The main effects of genotype on Dominance, Extraversion, Agreeableness, Neuroticism, and Openness were not significant. For Conscientiousness we found a significant main effect and a significant interaction: chimpanzees homozygous for L had higher scores on Conscientiousness than chimpanzees with other genotypes (P = 0.0158) and this association was stronger for males than for females (P = 0.0226). We also surveyed the reported indel in promoter region of arginine vasopressin receptor gene (AVPR1a) and found that chimpanzees with a copy of the long allele had higher scores on Conscientiousness (P = 0.0382).
