Taste-induced facial responses in black-handed spider monkeys (Ateles geoffroyi)

Sofia Pereira,Laura Teresa Hernandez Salazar,Matthias Laska

doi:10.1016/j.beproc.2021.104417

Sofia Pereira, Laura Teresa Hernandez Salazar + Show 1 more

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https://doi.org/10.1016/j.beproc.2021.104417

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Abstract

Taste-induced facial expressions are thought to reflect the hedonic valence of an animal’s gustatory experience. We therefore assessed taste-induced facial responses in six black-handed spider monkeys (Ateles geoffroyi) to water, sucrose, caffeine, citric acid and aspartame, representing the taste qualities sweet, bitter, and sour, respectively. We decided not to include salty-tasting substances as the concentrations of such tastants found in the fruits consumed by spider monkeys are below their taste preference threshold. We found that the monkeys displayed significant differences in their facial responses between substances, with significantly higher frequencies of licking, sucking, closed eyes, tongue protruding, mouth gaping and lip smacking in response to sucrose, a presumably pleasant stimulus. The response to caffeine and citric acid, in contrast, yielded the lowest frequencies of these behaviors, but the highest frequency of withdrawals from the stimulus, suggesting these substances are perceived as unpleasant. Lip stretching, a newly described behavior, was performed significantly more often in response to caffeine than to any other substance, suggesting an association with the response to bitter taste. The facial response to the artificial sweetener aspartame was generally similar to the response to water, corroborating the notion that Platyrrhines may be unable to detect its sweetness. Overall, the present study supports the idea of similarity of taste-induced facial responses in non-hominoid primates and humans, suggesting these displays to be evolutionarily conserved across the primate order.

Highlights

The hedonic valence of a taste stimulus is known to elicit charac teristic facial expressions in humans (Steiner and Glaser, 1995)
The facial response to sucrose was characterized by the highest fre quencies of licking, sucking, having the eyes closed or open less than 50 %, tongue protruding, mouth gaping and lip smacking compared to the four other taste stimuli included in the present study
The fact that water triggered approximately the same frequency of eyes open less than 50 % as did sucrose allows us only to conclude that this behavior may indicate either that the taste is perceived as pleasant or that it is perceived as neither pleasant nor unpleasant

Summary

Introduction

The hedonic valence of a taste stimulus is known to elicit charac teristic facial expressions in humans (Steiner and Glaser, 1995). In non-human primates, for example, previous studies have revealed distinct facial responses to at least two taste qualities (Steiner et al, 2001), with rhythmic tongue protrusions being associated with sweet taste and mouth gapes being associated with bitter taste. Previous studies showed that facial responses in nonhuman mammals may be a more sensitive indicator of the palatability and hedonic experience, i.e. the perceived pleasantness or unpleasant ness of food compared to the measurement of consumption (Hanson et al, 2016). As basically all food consumed by primates comprises a mixture of taste qualities (sweet, sour, bitter, salty, and umami), the study of facial re sponses may provide further insight into the trade-offs that e.g. frugiv orous primates have to make with regard to the attractive and aversive properties of different taste qualities and the ripeness of fruits

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