Breaking conversational rules matters to captive gorillas: A playback experiment

Loïc Pougnault,Florence Levréro,Alban Lemasson,Baptiste Mulot

doi:10.1038/s41598-020-63923-7

Abstract

Across human cultures, conversations are regulated by temporal and social rules. The universality of conversational rules suggests possible biological bases and encourages comparisons with the communicative interactions of nonhuman animals. Unexpectedly, few studies have focused on other great apes despite evidence of proto-conversational rules in monkeys, thus preventing researchers from drawing conclusions on potential evolutionary origins of this behaviour. A previous study showed however that western lowland gorillas engage in soft call interactions that seem temporally- and socially-ruled. Indeed, interactions occurred mainly between individuals close in age who followed a preset response delay, thus preventing call overlap. Here, we experimentally investigated the presence of these rules in a captive gorilla group, using a violation-of-expectation paradigm. Head orientation responses suggest that the respect of response delay matters to subjects, but the importance of the interlocutors’ age proximity appeared less clear. The intensity of the response varied with subjects’ age in a context-dependent way, supporting a possible role of learning. Our findings support the growing number of studies highlighting the importance of vocal turn-taking in animals and a possible sociogenesis of this ability. The capacity to “converse” might have been a key step in the co-evolution of communication and complex sociality.

Highlights

Despite the diversity of human cultures, some basic conversational rules are respected in all societies and appear universal[1]
To facilitate cross species investigations, authors typically distinguish “conversation-like vocal exchanges” from other vocal patterns like isolated calling, repeated calling, disorganized phonoresponses, chorusing and duetting
A recent study on marmosets, focusing on long periods of vocal interactions, showed such temporal coordination of vocal productions between individuals[32]. Another important rule shared by human, nonhuman primates and several other animal species is that exchanging partners are not randomly nor opportunistically chosen

Summary

Introduction

Despite the diversity of human cultures, some basic conversational rules are respected in all societies and appear universal[1]. “conversation-like vocal exchanges” are not restricted to a specific context, which differs from – usually long-distance – collective communication associated with mate attraction, territory protection and environmental disturbance[21], and time of the day or year (excluding morning choruses and reproductive signals[22,23]). A recent study on marmosets, focusing on long periods of vocal interactions, showed such temporal coordination of vocal productions between individuals[32] Another important rule shared by human, nonhuman primates and several other animal species is that exchanging partners are not randomly nor opportunistically chosen (bottlenose dolphins[28], large-billed crows Corvus macrorhynchos[33], meerkats Suricatta suricatta[34], sperm whales[27], elephants[35]). The current state of knowledge prevents to conclude between a convergent evolution guided by the requirements of social life or a shared inheritance, suggesting an ancient mechanism which was already present in the primate lineage

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