Erin Kinnally; John Capitanio; Elizabeth Wood; Angus Bennion; Ryno Kruger; Christina Barr; Stephen Lindell; Stephen Suomi, Brigham Young University
Studies show that social relationships play a role in physical and mental health and that an individual’s genetic variation may influence their sociability. It is widely believed that the serotonin and oxytocin systems influence social behavior. The two variants of the serotonin transporter (SERT) gene code for efficiency of the serotonin system, with the long (L) allele associated with greater efficiency and the short (s) allele associated with lower efficiency. The two variants of the oxytocin receptor (OXTR) gene code for availability of oxytocin, with the ancestral allele (G) associated with increased oxytocin availability and the mutant allele (A) leading to lower availability. While these genes are present in humans, orthologous SERT and OXTR genes are present among rhesus macaques (Macaca mulatta), a nonhuman primate species commonly used in translational research assessing genetic contributions to behavior due to their genetic, social, and physiological similarities to humans. To assess the contributions of SERT and OXTR genotypes to social behavior, at three-to-four months of age, blood samples were obtained from 127 rhesus monkeys (55 males, 72 females) housed in large social groups of 100 or more members. DNA was extracted and genotyped for the SERT genotype for all subjects and OXTR genotype for 33 subjects. As adults (M=6.23 years), subjects’ affiliative behaviors (e.g., number of social partners, rates of grooming, initiating social affiliation, and their frequency of social proximity) were recorded by trained observers during four 300-second observations. One-way ANOVA with genotype as the independent variable and social behaviors as the dependent variables were used to determine the relationship between genotype and affiliative behaviors. An association between SERT genotype and subjects’ average number of social partners neared traditional statistical significance (F(2,117)=2.749, p = 0.068), with a posteriori analyses showing that subjects homozygous for the L allele exhibited significantly more social partners when compared to subjects homozygous for the s-allele subjects. Further, OXTR genotype was associated with the frequency of receiving groom from social group members (F(2,26)=8.058, p = 0.002), with a posteriori analyses showing that subjects that were homozygous for the A allele showed increased rates of being groomed by others when compared to subjects with other genotypes. These findings suggest that subjects homozygous for the L allele for the SERT gene and subjects homozygous for the A allele for the OXTR genotype showed evidence for greater affiliation than do subjects with other genotypes.