Short-Term Reciprocity in Macaque’s Social Decision-Making

Abstract

Primates live in complex social environments, where individuals create meaningful networks by adapting their behavior according to past experiences with others. Although free-ranging primates do show signs of reciprocity, experiments in more controlled environments have mainly failed to reproduce such social dynamics. Hence, the cognitive and neural processes allowing monkeys to reciprocate during social exchanges remains elusive. Here, pairs of long-tailed macaques (Macaca fascicularis) took turns into a social decision task involving the delivery of positive (juice reward) or negative (airpuff) outcomes. By analyzing the contingencies of one partner’s past decisions on the other’s future decisions, we demonstrate the presence of reciprocity, but only for the exchange of negative outcomes. Importantly, to display this decisional bias, the monkey needs to witness its partner’s decisions, since non-social deliveries of the same outcome did not have such effect. Withholding of negative outcomes also predicted future social decisions, which suggest that the observed tit-for-tat strategy may not only be motivated by retaliation after receiving an airpuff but also by the gratefulness of not having received one. These results clarify the apparent dichotomy within the scientific literature of reciprocity in non-human primates and suggest that their social cognition comprise revenge and gratitude.

Impact of internal and external factors on prosocial choices in rhesus macaques

“…Therefore, a different protocol varying the order in which the different targets are learned and with different targets for each experimental condition should be considered in future studies. Finally, although kinship, social proximity between actor, and partner or ingroup versus outgroup effects have been shown to impact on social behaviours in apes and rhesus monkeys [43,65], we did not observe within-subject variability in performance in regards to the two familiar partners tested. Using familiar and unfamiliar partners might have resulted in different prosocial bias.…”

“…In our paradigm, however, neither the identity of the partner monkey nor its behaviour modulated the prosocial tendencies of the actor monkeys. Based on previous studies showing evidence of reciprocity in Prisoner's Dilemma games [19,43], we were expecting that forcing the partner to make selfish decisions would result in a decrease in the prosocial bias of the actor. This was not, however, the case.…”

“…Rhesus macaques are more likely to behave cooperatively in a Prisoner's Dilemma game if the partner has made a cooperative choice on the previous trial [19]. Reciprocity has also been observed in contexts in which long-tailed macaques withhold delivering a punishment [43].…”

Is this worth the trouble? Strategic conflict management in Tonkean macaques

“…Tit-for-tat strategies may be a way for subordinates to impose a cost on the aggression of the dominant. 56 , 57 Monkeys may also see social conflict as a disruption to others (such as preventing others from getting juice rewards in our case). Such high-order prosocial consideration would arguably rely on empathy and perspective taking abilities and may be influenced by kinship and previous existing social links between individuals.…”