FACTORS AFFECTING RATES OF SOCIAL BUFFERING IN JUVENILE RHESUS MACAQUES (Macaca mulatta)

Abstract

The purpose of the current study was to investigate genetic and experiential contributions to social buffering between juvenile non human primates. A second aim was to investigate the role of behavioral displays during social buffering, in order to explain social buffering deficits in primates with a history of early social deprivation (Winslow et al., 2003). A total of 31 male rhesus macaques (mean age of 2 years) were videotaped during a Novel Cage Test with and without their homecage partner, and immediately following, blood samples were collected under anesthesia. Subjects were either reared with mothers and peers (mother reared, <italic>n</italic>=15) or without their mothers in the continuous presence of peers (peer reared, <italic>n</italic> =16). Cortisol concentrations and rh5-HTTLPR genotypes (long (<italic> l </italic>) and short (<italic> s </italic>) alleles) were generated from blood samples (<italic> l/l </italic> =20, <italic> l/s </italic>=10, and <italic> s/s </italic>=1), and videos were coded for a variety of stress and affiliation behaviors.

Genotype and rearing differences in social buffering of stress behaviors and neuroendocrine function were assessed. Rates of social buffering were also compared between a group of high display subjects that exhibited frequent behavioral displays (<italic>n</italic> =21) compared to a low display group (<italic>n</italic>=10). Additionally, the behavioral data were subjected to a lag sequential analysis to examine levels of contingent responsiveness, or the likelihood of behavioral displays occurring before affiliative responses (Bakeman et al., 1997).

The results revealed social buffering deficits in the short allele, peer reared, and low display groups. Both the peer reared and low display groups were found to engage in less affiliative behaviors compared to the mother reared and high display groups respectively, while the short allele group appeared to receive less benefit from the presence of a familiar partner. Additionally, contingent responsiveness was identified as a feature of social buffering for the entire sample, but did not explain group differences in social buffering. Taken as a whole, this study identifies genetic and experiential vulnerability factors for social buffering. Furthermore, it adds to our knowledge of how behavioral displays are used during social buffering.