Foraging postures are a potential communicativesignal in female bonobos

Elisa Demuru,Florence Levréro,François Pellegrino,Dan Dediu

doi:10.1038/s41598-020-72451-3

Abstract

Body postures are essential in animal behavioural repertoires and theircommunicative role has been assessed in a wide array of taxa and contexts. Some bodypostures function as amplifiers, a class of signalsthat increase the detection likelihood of other signals. While foraging on the ground,bonobos (Pan paniscus) can adopt different crouchingpostures exposing more or less of their genital area. To our knowledge, their potentialfunctional role in the sociosexual life of bonobos has not been assessed yet. Here weshow, by analysing more than 2,400 foraging events in 21 captive bonobos, that maturefemales adopt a rear-exposing posture (forelimb-crouch) and do so significantly more often when their anogenitalregion is swollen than during the non-swollen phase. In contrast, mature males almostcompletely avoid this posture. Moreover, this strong difference results from a divergingontogeny between males and females since immature males and females adopt the forelimb-crouch at similar frequencies. Our findings suggestthat the forelimb-crouch posture may play acommunicative role of amplification by enhancing the visibility of female sexualswellings, a conspicuous signal that is very attractive for both males and females.Given the high social relevance of this sexual signal, our study emphasizes thatpostural signalling in primates probably deserves more attention, even outside ofreproductive contexts.

Highlights

In contrast with the full-crouch posture, the forelimb-crouch posture has the peculiarity of exposing the anogenital area, but this postural behaviour has never been investigated as a potential communicative signal
Focusing on mature females (Fig. 2b), we found that while their posture is not affected by hierarchical rank (p = 0.71), it does change with swelling (p = 2.73∙10–13): at intermediate and maximum swelling phases there is a higher probability of forelimb-crouching (69.0% and 66.3%) than at minimum swelling phase (49.6%), this relationship being non-linear
Our results show that whereas immature bonobos did not show any significant sex differences in positional preference, mature bonobos displayed strong preferences either to adopting the rear-exposing forelimb-crouch or to avoiding it. The changes in their postural behaviours through their sexual swelling cycle suggest a stronger preference for forelimb-crouching during the swelling phases over the non-swelling phase

Summary

Introduction

In contrast with the full-crouch posture, the forelimb-crouch posture has the peculiarity of exposing the anogenital area, but this postural behaviour has never been investigated as a potential communicative signal Both postures typically coexist in each individual’s repertoire and, to the best of our knowledge, it is still unknown whether social or ecological factors influence these postural behaviours. In this observational study focussing on the emitter’s perspective, we provide a thorough analysis of the occurrence of forelimb-crouch and full-crouch in bonobos by putting these two body postures in relation with individual features, such as age, gender, and reproductive and hierarchical status. We predict that adult females adopt this posture more frequently than adult males and immature subjects, and that this posture is preferred when the sexual swelling is in the maximum phase

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Conclusion