Ape duos and trios: spontaneous cooperation with free partner choice in chimpanzees

Abstract

The purpose of the present study was to push the boundaries of cooperation among captive chimpanzees (Pan troglodytes). There has been doubt about the level of cooperation that chimpanzees are able to spontaneously achieve or understand. Would they, without any pre-training or restrictions in partner choice, be able to develop successful joint action? And would they be able to extend cooperation to more than two partners, as they do in nature? Chimpanzees were given a chance to cooperate with multiple partners of their own choosing. All members of the group (N = 11) had simultaneous access to an apparatus that required two (dyadic condition) or three (triadic condition) individuals to pull in a tray baited with food. Without any training, the chimpanzees spontaneously solved the task a total of 3,565 times in both dyadic and triadic combinations. Their success rate and efficiency increased over time, whereas the amount of pulling in the absence of a partner decreased, demonstrating that they had learned the task contingencies. They preferentially approached the apparatus when kin or nonkin of similar rank were present, showing a preference for socially tolerant partners. The forced partner combinations typical of cooperation experiments cannot reveal these abilities, which demonstrate that in the midst of a complex social environment, chimpanzees spontaneously initiate and maintain a high level of cooperative behavior.

Cooperation in wild Barbary macaques: factors affecting free partner choice

“…For example, chimpanzees were able to recruit a cooperative partner (by unlocking a door) only when solving the problem required cooperation, and they recruited the most efficient partner (chosen between two available individuals) based on their experience with each of them on a previous day (Melis et al 2006a). In a recent study, captive chimpanzees spontaneously initiated and maintained a high level of success in solving cooperative tasks when given the choice of freely choosing their partners (Suchak et al 2014). …”

“…Individuals may be less willing to cooperate with higher ranking partners, which often monopolise experimental apparatuses that dispense food (Chalmeau and Gallo 1993;de Waal and Davis 2003;Drea and Carter 2009;Suchak et al 2014). The temperament of the subjects may also affect cooperation (Bergmüller et al 2010;McNamara and Leimar 2010).…”

“…Pulling in the absence of a partner often never fully disappears in cooperative experiments conducted on animals (e.g. Mendres and de Waal 2000;Cronin et al 2005;Suchak et al 2014). Several hypotheses may explain this result.…”

“…There is evidence that many animals have difficulties to inhibit a learned response (here pulling a string) to get food (Stevens and Hauser 2004;Péron et al 2011). Indeed, pulling requires very low energy expenditure which might explain why extraneous pulling is not inhibited completely (Suchak et al 2014). Fourth, the fluctuation of success rate across sessions may be due to the variations of duration, trials and availability of partner across sessions.…”

“…For example, chimpanzees cooperated with partners ranking higher than themselves only if the partners were relatives (Suchak et al 2014). Although it would have been interesting to investigate whether cooperative interactions were predicted by kin relationships between the study animals, kinship was not known for our study group.…”