Not all yawns tell the same story: The case of Tonkean macaques

Abstract

Here we show for the first time that the plasticity in morphology and duration of yawning in Macaca tonkeana can be associated with different functional contexts.Macaca tonkeana is classified as a tolerant macaque species characterized by social interactions minimally constrained by dominance rank or kinship. Tonkean macaques, as other egalitarian species, rely on a complex facial communicative system.We found that the degree of mouth opening (ranging from covered to uncovered tooth yawns) and the duration of yawning were not strictly dependent. The shortest uncovered tooth yawns were associated with an intense locomotor/physical activity and peaked immediately after stressful social events thus indicating an increase in arousal. In contrast, longer yawns, independently from teeth exposure, were primarily associated with a relaxed state of the subject. In conclusion, our study suggests that to explore the potential different functions of yawning, it is necessary to focus on the variability of its expression both in terms of morphology and duration, because not all yawns tell the same story.

Factors affecting yawning frequencies in preterm neonates

“…During the last decades, several theories have been formulated to explain the evolutionary origins of yawning, each identifying different modulating factors as the core function of this behavioral pattern, including arousal/vigilance [1,18], brain thermoregulation [19], cortisol levels regulation [20], empathy and social interaction [3,21]. Despite this tendency to trace the origins of yawning back to a single function, recent studies have highlighted in some primates a surprising morphological and temporal variability in yawns, associated with different conditions and social contexts [22][23][24], suggesting that yawning might serve different functions in different circumstances [24].On the other hand, although these theories have been often presented as competing explanatory alternatives, several scholars have highlighted the need of distinguishing proximate and ultimate explanations when investigating mechanisms underlying the manifestation of yawning behavior [25]. In particular, advocates of the brain cooling hypothesis have argued that, while, e.g., empathy, familiarity or communication might serve as proximal mechanisms explaining yawning modulation, the ultimate function(s) of yawning is likely physiological and should be able to explain proximate mechanisms as well [26].…”

Yawning informs behavioural state changing in wild spotted hyaenas

“…Yawns seem to be more flexible in primates that are characterised by a high complexity in their facial musculature (Davila-Ross and Palagi 2022). In this mammalian order, the behaviour can vary in frequency, duration and motor execution as a function of the age of the subjects (Deputte 1994;Leone et al 2014) and the contexts in which the behaviour occurs (Zannella et al 2021). Further data on spontaneous yawning variability in both social carnivore and primate species are needed to understand if the phenomenon actually differs in these two lineages of mammals.…”

“…frequency, duration, morphology). It has been demonstrated that yawn variation can predict the different physiological causes on the basis of its emission (Vick and Paukner 2010;Zannella et al 2021). For example, yawning rates can be age-dependent, with juveniles yawning less than adults (Giganti and Salzarulo 2010).…”

“…For example, yawning rates can be age-dependent, with juveniles yawning less than adults (Giganti and Salzarulo 2010). Moreover, frequency, duration and motor execution are also context-dependent with shorter and more frequent yawns being performed during arousal situations in several primate groups (Deputte 1994;Zannella et al 2021). In some species of social carnivores, yawning is not affected by age; it is mainly performed under resting conditions and is consistent in its duration and performance (lions, Casetta et al 2021; South American sea lions, Palagi et al 2019a, b).…”

Playing together, laughing together: rapid facial mimicry and social sensitivity in lowland gorillas

“…The ability to read and appropriately interpret the signals emitted by conspecifics is an essential element for the success of sociality in humans and other highly social species ( Freeberg et al 2012 ; Demuru et al 2015 ; Arnold and Winkielman 2020 ; Casetta et al 2021 ; Nolfo et al 2021 ). Among the bodily signals produced by primates, being more dynamic, nuanced, and rapid, facial expressions represent an efficient communicative channel employed in diverse social contexts, such as aggression, sex, and play ( de Waal 1988 ; Palagi 2008 ; Cordoni and Palagi 2011a ; Chen et al 2018 ; Cordoni et al 2018 ; Palagi et al 2020a ; Zannella et al 2021 ). Having access to the face of the partner is therefore crucial to perceive and interpret their facial expressions in an appropriate way both at intra- and inter-specific level ( Palagi and Mancini 2011 ; Prochazkova and Kret 2017 ; Annicchiarico et al 2020 ; Maglieri et al 2020 ).…”