Spontaneous Yawning and its Potential Functions in South American Sea Lions (Otaria flavescens)

Abstract

Spontaneous yawning is a widespread behaviour in vertebrates. However, data on marine mammals are scarce. In this study, we tested some hypotheses on the functions of yawning in a captive group of South American sea lions (Otaria flavescens). According to the Dimorphism Hypothesis, species showing low levels of sexual dimorphism in canine size do not show sex differences in yawning distribution; this was supported by our findings, since yawning did not differ between the sexes. Yawning was more frequently performed during resting/sleeping contexts, thus supporting the Drowsiness Hypothesis. Yawning and self-scratching are considered reliable indicators of short-term anxiety in sea lions, since they immediately increased after conflicts both in aggressors and victims (Social Distress Hypothesis supported). In the long-term, yawning was not correlated with individuals’ dominance status, thus showing that anxiety is similarly experienced by dominants and subordinates. The last two findings can be explained by the social competition of this species, that involves individuals independently from their sex, age or ranking status. Therefore, the exposure to frequent stressful events can induce similar levels of anxiety in all the subjects (Resource Inequity Hypothesis supported). In conclusion, spontaneous yawning in sea lions seems to share similar functions with other social mammals, suggesting that this behaviour is a possible plesiomorphic trait.

Human-Dog Relationship during the First COVID-19 Lockdown in Italy

“…Several physiological and social hypotheses have been formulated about the functions of spontaneous yawning in non-human animals. Indeed, yawning could act as a homeostatic brain-restoring and -cooling mechanism and a signal of anxiety and sleepiness and plays a role in the social communication system as well [ 62 ]. Therefore, in the context of the relationship, the yawn also has another value: It seems to mix with the emotional contagion, which is defined as “the tendency to automatically imitate and synchronize expressions, vocalizations, postures and movements with those of another person and, consequently, to emotionally converge” [ 63 ].…”

Intraspecific Motor and Emotional Alignment in Dogs and Wolves: The Basic Building Blocks of Dog–Human Affective Connectedness

“…This first evidence of social modulation of yawn contagion was quickly challenged. In many species, including dogs, spontaneous yawning can emerge in response to environmental or social stressors [63,[78][79][80]. In this light, it has been suggested that the finding obtained by Silva and colleagues [25] could be simply ascribed to a distress response by dogs.…”

“…It cannot be considered as a facial expression because it recruits facial, oral, laryngeal, pharyngeal, thoracic and abdominal muscles. Indeed, depending on the species, yawning may be also accompanied by eye closing, vocalizations, body stretching, pandiculation and even tongue protrusion [63]. Yawning is a widespread phenomenon in mammals and birds [64,65].…”

“…Several hypotheses on the functions of spontaneous yawning in non-human animals have been formulated and these involved both physiological and social explanations. Indeed, yawning could act as a homeostatic restoring and brain cooling mechanism, an anxiety and drowsiness signal, and it has also a role in the social communicative system (e.g., threat or alertness yawn) [63].…”

Yawning informs behavioural state changing in wild spotted hyaenas

“…In many vertebrate species, a yawn punctuates the switch from the awake to the sleepy phase (and vice versa) (e.g. ostriches, Struthio camelus australis, Sauer and Sauer 1967;human, Provine 2005; red hill salamanders, Phaeognathus hubrichti, Bakkegard 2017; South American sea lions, Otaria flavescens, Palagi et al 2019a; African lions, Panthera leo, Casetta et al 2021;dugongs, Dugong dugon, Enokizu et al 2022; bottlenose dolphins, Tursiops truncatus, Enokizu et al 2021;non-human primates, Zannella et al 2021). In this context, yawning increases alertness, thus making subjects able to adjust their behaviour in response to sudden and unexpected situations (Provine 2005;Gallup 2022).…”