Mason Bennett, Brigham Young University
Social and Behavioral Sciences
In the natural environment, rhesus macaques (Macaca mulatta) acquire social dominance rank through matrilineal family (mothers’) inheritance. It is unknown as to how high ranking matrilines initially become high in social dominance. Serotonin (5HT) has been linked to social dominance rank. Central Nervous System 5HT is modulated by both the serotonin transporter (5HTT) and MAO and both have been linked to social dominance rank. MAOa and the 5HTT are the two main variables controlling central serotonin. To assess the effects of genetic and temperamental variables on matrilineal rank and potentially the effects of rank on behavior and temperament, we examined: the serotonin transporter genotype and MAOa genotypes. Because low or unstable social dominance rank is stressful, leading to chronic hypercortisolemia we also measured stress-induced cortisol levels. Lastly we examined infant temperament ratings taken from a Bio-Behavioral Assessment (BBA) pioneered by John Capitanio. This test is performed over a 24 hour period when infants are 6 months of age, and includes a bio-behavioral battery of tests designed to measure temperament. Dominance was measured by wins/losses during head-to-head competition between all possible pairs in a group. Subjects included 2300 rhesus macaques raised at the California National Primate Research Center between the years of 2001-2012. Results showed that matrilines high in social dominance exhibited a significantly high rate of both the long allele of the serotonin transporter genotype, and for males a high frequency of MAOa allele 6. As infants, subjects from matrilines low in social dominance rank exhibited high cortisol, hypervigilance, low activity ratings, and high emotionality. This study is the first of its kind to suggest that the acquisition of dominance by a matriline is modulated by genetic influences and that it is likely that the serotonin system plays a role in this process.