Short-Term Reciprocity in Macaque's Social Decision-Making.

Sébastien Ballesta,Jean-René Duhamel,Gilles Reymond

doi:10.3389/fnbeh.2019.00225

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.

Highlights

During exchanges of positive or negative actions between individuals, prior outcomes may influence further social interactions
We scored the previous blocks using only the number of a given outcomes delivery and performed similar analysis. We found that both the numbers of airpuffs delivered to nobody and to the actor by the partner were significant predictors of the actor’s social decisions involving airpuff deliveries (Figure 2D, Number of airpuffs delivered to nobody: GLME, R2 = 0.57, F = 21.3, p < 0.001; Number of airpuffs delivered to the partner: GLME, R2 = 0.46, F = 10.3, p = 0.006)
Similar analysis using the number of the outcomes from other types of decision was not significantly predicting the actors’ social decisions (Number of juice delivered to the partner: GLME, R2 = 0, F = 0.09, p = 0.76; number of juice delivered to nobody: GLME, R2 = 0.15, F = 1, p = 0.32; number of airpuff delivered to the actor by the actor: GLME, R2 = 0.13, F = 2.47, p = 0.14; number of airpuff delivered to nobody by the actor: GLME, R2 = 0, F = 0, p = 0.94)

Summary

Introduction

During exchanges of positive or negative actions between individuals, prior outcomes may influence further social interactions. Under experimentally controlled conditions, monkeys failed to display signs of reciprocity (Brosnan et al, 2009; Yamamoto and Tanaka, 2009; Pelé et al, 2010; Suchak and de Waal, 2012; Claidière et al, 2015). This apparent lack of valuation of prior exchanges might be interpreted in several ways, such as real absence of short-term. We designed a task where two monkeys faced each other, and alternately made social decisions involving juice or airpuff delivery to the partner or to an empty space (called ‘‘nobody’’ hereafter; Ballesta and Duhamel, 2015). The interpretation of its significance by non-human primates may be more straightforward than that of a food (or juice) exchange, which is, for instance, affected by several other factors such as satiety, spatial proximity of peers, and social hierarchy (Watson and Caldwell, 2009)

Methods

Results

Conclusion