Abstract # 229:

Scheduled for Saturday, August 19, 2006 01:30 PM-01:45 PM: Session 22 (Regency East #1) Oral Presentation

Market forces predict grooming reciprocity in rhesus macaques under diverse population densities

P. G. Judge1 and F. B. de Waal2
1Bucknell University, Psychology Department and Animal Behavior Program, Lewisburg, PA 17837, USA, 2Living Links, Yerkes National Primate Research Center, Emory University
     A biological market perspective proposes that primates use grooming for reciprocal exchange to cultivate valuable social partners and to interchange commodities such as grooming for tolerance near resources. At high population density with increased risk of aggression, subordinates might trade grooming for tolerance, while at lower density grooming may be more reciprocal to maintain preferred social relationships. Predictions were tested by examining grooming reciprocity and rank distance among adult females in six similar-sized groups of rhesus macaques (Macaca mulatta) living under three different density conditions (low = free-ranging, medium = outdoor corrals, and high = small enclosures). Pearson correlations of all paired dyads in each condition evaluated for significance through resampling indicated that grooming was not reciprocated at high density (r=-0.03, N=166, ns) but was reciprocated (p<0.05) at medium density (r=+0.15, N=211) and low density (r=+0.42, N=143). Comparison of the slopes of the regression lines indicated that grooming was significantly more reciprocal at low density than at medium and high density (p<0.01). Rank distance was not related to the degree of grooming reciprocity at low and medium density, but at high density grooming was negatively reciprocated among distantly ranked animals (r=-0.54, N=15, p<0.03). Grooming became less reciprocal as density increased particularly among distantly ranked partners, suggesting that market forces may have promoted grooming for tolerance at higher density. Support: NIH RR05276, RR00165, RR00167.