Social Integration of Rhesus Monkeys into All-Male Groups: A New Context for the Social Amygdala Open Access

Abstract

Abstract

Social Integration of Rhesus Monkeys into All-Male Groups:

A New Context for the Social Amygdala

Among primates, male emigration presents sex-specific social challenges. Male rhesus macaques (Macaca mulatta) emigrate from their natal groups and must successfully integrate into new social groups in order to ensure their survival and reproductive success. Thus, juvenile male rhesus monkeys are a unique model in which to study the neural mechanisms of social behavior. The amygdala has long been implicated in various aspects of social behavior, and lesions of the amygdala have been shown to produce deficits in producing appropriate social responses. In the present study, I have examined social behavior following neonatal amygdalectomy in juvenile male rhesus monkeys (n = 18) reared in semi-natural social groups to determine the extent to which social rearing environment attenuates the behavioral effects of neonatal amygdala lesions. MRI-guided, ibotenic acid-induced lesions of the amygdala (n = 9) or sham procedures (n = 9) were performed at 4 weeks of age. Males then spent the next two years of life in large, mixed-sex, multifamily groups. At 2-2.5 years of age, subjects were removed from their natal groups and all-male groups of age-matched animals were formed in order to present males with an ecologically relevant social challenge. Results indicate that operated males are less likely to initiate social interaction during acute social challenges, but are not impaired in their ability to produce and respond to contextually appropriate social signals. However, this effect is attenuated by social context; observations conducted over a period of months in stable social groups reveal no significant differences between operated and control males and also provide evidence that operated males do not characteristically assume low social rank, as has been previously suggested. These results suggest that a complex social rearing environment compensates for early loss of the amygdala and underscore an important difference in behavioral outcomes as a result of the testing environment. Thus, a relevant social context is crucial to facilitating a deeper understanding of the neural mechanisms of social behavior.

Table of Contents

Table of Contents

I. Introduction........................................................................1

Natal male emigration..................................................3

The amygdala and social behavior................................10

Current research........................................................27

II. Methods...........................................................................30

Subjects....................................................................31 Surgical procedures.....................................................31 Pair introductions........................................................32 Group introductions.....................................................34 Behavioral observations...............................................34 Data analysis..............................................................35 III. Results............................................................................37 Group introductions.....................................................38

Affiliative behaviors.............................................38

Aggressive behaviors...........................................39

Dominance-related behaviors................................39

Play behaviors.....................................................40

Sexual and other behaviors...................................41

Focal observations........................................................51

Affiliative behaviors..............................................51

Aggressive behaviors............................................52

Dominance-related behaviors.................................53

Play behaviors......................................................54

Sexual and other behaviors....................................54

Social dominance rank...........................................66

IV. Discussion.........................................................................70

Group introductions.......................................................71 Focal observations.........................................................76 General discussion.........................................................79 V. Appendix............................................................................83 VI. References.........................................................................92

About this Master's Thesis

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School	Laney Graduate School
Department	Psychology
Degree	MA
Submission	Master's Thesis
Language	English
Research Field	Psychology, General
Keyword	social dominance rhesus monkey social behavior amygdala
Committee Chair / Thesis Advisor	Wallen, Kim, Emory University
Committee Members	McDowell, Jack J, Emory University Gouzoules, Harold, Emory University

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