Abstract # 3160 Event # 53:

Scheduled for Saturday, September 17, 2011 03:15 PM-03:30 PM: Session 11 (Meeting Room 408)


SQUIRREL MONKEYS’ RESPONSE TO INEQUITABLE OUTCOMES INDICATES A BEHAVIORAL CONVERGENCE WITHIN THE PRIMATES

C. F. Talbot1,2, H. D. Freeman1,2, L. E. Williams2 and S. F. Brosnan1,2,3
1Georgia State University, Department of Psychology, Atlanta, Georgia, USA, 2Michale E Keeling Center for Comparative Medicine and Research of the University of Texas M. D. Anderson Cancer Center, Department of Veterinary Services, Bastrop, TX USA, 3Neuroscience Institute, Georgia State University, Atlanta, GA USA
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     Several primates respond negatively to inequity, however, it is unknown how this reaction evolved. Responses to inequity may be homologous within primates. Alternative hypotheses posit that this response evolved as a mechanism to promote cooperation. Thus far, the primates in which inequity responses have been documented are all cooperative and gregarious (Homo sapiens, Pan troglodytes, Cebus apella), making it difficult to distinguish between homology and a convergence based on these traits. We tested this hypothesis by investigating the response to inequity in twelve pairs of socially-housed squirrel monkeys (Saimiri sciureus and S. boliviensis), which share a phylogenetic Family with capuchin monkeys, but do not cooperate extensively. Subjects exchanged tokens to receive food rewards in conditions which varied in effort required and reward received. Squirrel monkeys did not respond negatively to inequity (Sign-Rank Test, T+=137, n=22, p=0.733). However the monkeys were sensitive to the variation present in the task; male subjects showed a contrast effect (Sign-Rank Test, T+=74.5, n=13, p=0.042) and, as in previous studies, subjects were more sensitive to differences in reward in the context of a task than when rewards were given for free (Sign-Rank Test, T+=283, n=24, p<0.001). Taken with other results, these results support the hypothesis that a negative response to inequity evolved convergently in primates, likely as a mechanism for evaluating outcomes relative to one’s partners in cooperative species.