RECIPROCITY AND INTERCHANGE OF GROOMING AND SUPPORT IN CAPTIVE CHIMPANZEES

Reciprocity and interchange of grooming and coalition formation of captive chimpanzees, Pan troglodytes, were studied at a group level as (partial) correlations between an actor matrix and a receiver matrix. Periods in which one male clearly occupied the alpha-position and those in which his position was unclear, because not all males behaved submissively towards him, were distinguished. Males appeared to reciprocate grooming in both types of period, but reciprocated support in conflicts only when the alphaposition was unclear. This may reflect a directly selfish strategy. In periods with a clear alpha-male position, males supported more often those they groomed more frequently, suggesting a social bond. In addition, males interchanged grooming for received support, but this seemed to be a by-product of correlations of each variable with received grooming. Correlations with dominance rank were notable: the higher the rank of the partners the more often males supported them. Further, males also more frequently received support and opposition by intervention from higher ranked partners. Grooming and support relationships of females were the same whether or not the alpha-male position was clear. Grooming appeared to be reciprocated and was associated with support, indicating a social bond. Furthermore, the correlation for interchange between grooming and support received was found to be genuine, but the reverse correlation between support and grooming received was not. Thus, interchange occurred in one direction only. Neither males nor females reciprocated opposition by means of aggressive intervention. © 1991.