The popularity of this idea seems inversely correlated to the quantity of data supporting it, but here are some interesting exceptions:

• Carne, C., Wiper, S. & Semple, S. 2011. Reciprocation and interchange of grooming, agonistic support, feeding tolerance, and aggression in semi-free-ranging Barbary macaques. American Journal of Primatology, 73, 1127-1133

• Ventura, R., Majolo, B., Koyama, N. F., Hardie, S. & Schino, G. 2006. Reciprocation and interchange in wild Japanese macaques: grooming, cofeeding, and agonistic support. American Journal of Primatology, 68, 1138-1149

• Watts, D. P. 2000. Grooming between male chimpanzees at Ngogo, Kibale National Park. II. Influence of male rank and possible competition for partners. International Journal of Primatology, 21, 211-238.