Chimpanzee lip-smacking facilitates cooperative behaviour.

Pawel Fedurek,Katie E Slocombe,Klaus Zuberbühler,Jessica A Hartel

doi:10.1038/srep13460

Pawel Fedurek, Katie E Slocombe + Show 2 more

Open Access

https://doi.org/10.1038/srep13460

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Abstract

Signalling plays an important role in facilitating and maintaining affiliative or cooperative interactions in social animals. Social grooming in primates is an example of an interaction that requires coordination between partners but little is known about communicative behaviours facilitating this activity. In this study, we analysed the communication of wild chimpanzees of Budongo Forest, Uganda, as they entered and maintained a naturally occurring cooperative interaction: social grooming. We found that lip-smacking, a distinct multimodal oral gesture produced during grooming, coordinated this activity. Lip-smacking at the beginning of grooming bouts was significantly more often followed by longer and reciprocated bouts than silent grooming initiations. Lip-smacks were more likely to be produced when the risk of termination of the interaction by the recipient was high, for instance when grooming vulnerable body parts. Groomers were also more likely to produce lip-smacks during face-to-face grooming where the visual aspect of the signal could be perceived. Data are consistent with the hypothesis that chimpanzee lip-smacks function to coordinate and prolong social grooming, suggesting that this oral signal is an example of a communicative behaviour facilitating cooperative behaviour in chimpanzees.

Highlights

The criteria of a cooperative act[30] defined as a social interaction that, regardless of short-term costs, increases fitness[31]
Lip-smacking is a good candidate to function in this manner, since it is often associated with grooming. This especially applies to chimpanzees, which, in contrast to monkey species, produce lip-smacks almost exclusively in grooming contexts
We predicted that the groomee would be more likely to reciprocate grooming if lip-smacks were given by the groomer, and that groomers would be more likely to produce lip-smacks when engaging in higher-risk grooming of vulnerable body parts, to signal benign intent and to prevent early termination of the grooming bout by the recipient (e.g.,22,35)

Summary

Introduction

The criteria of a cooperative act[30] defined as a social interaction that, regardless of short-term costs, increases fitness[31]. Lip-smacking is a good candidate to function in this manner, since it is often associated with grooming This especially applies to chimpanzees, which, in contrast to monkey species, produce lip-smacks almost exclusively in grooming contexts. In chimpanzees lip-smacks are produced by the groomer[32] when initiating or during grooming bouts[33,34], suggesting it plays a role in coordinating this social interaction. We predicted that the groomee would be more likely to reciprocate grooming if lip-smacks were given by the groomer, and that groomers would be more likely to produce lip-smacks when engaging in higher-risk grooming of vulnerable body parts, to signal benign intent and to prevent early termination of the grooming bout by the recipient (e.g.,22,35). Since lip-smacking is a multimodal signal, we predicted that lip-smacking would be more frequent when partners were facing each other and recipients could detect the visual component of the signal (e.g.,36)

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