Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
 
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
 
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
http://www.baillement.com

mystery of yawning 

 

 

mise à jour du
30 août 2021
Behav Processes
2021 Aug; 189:104444
Yawn-like behavior in captive common
bottlenose dolphins (Tursiops truncatus)

Enokizu A, Morisaka T, Murakami K, Sakurai N,

Ueda N, Yoshioka M.

Chat-logomini

Abstract
Yawning is an involuntary action that begins with a slow opening of the mouth with inhalation, followed by a maximum gaping phase, and ends with a short exhalation and the closing of the mouth. A wide variety of vertebrate species, including humans, yawn. Here, we report underwater yawn-like behavior in three captive common bottlenose dolphins, inferred from 119-h of observations. Five cases of yawn-like behavior were selected out of 2045 open-mouth behaviors, after removing intentional open-mouth behaviors. Yawn-like behaviors were chosen that had a mouth open-close duration ratio of 1 (duration of Phase 3, the period of mouth closing after maximum opening, divided by the duration of Phase 1, the period of mouth opening from start to maximum opening). Naïve human evaluators selected "yawn-like" behaviors. All five cases of yawn-like behavior occurred during inactive periods, similar to human yawns. In three of the five cases, inactivity levels significantly decreased within 4 min after the yawn-like behavior; therefore, yawn-like behavior in dolphins may increase their arousal level in drowsy states. Thus, the yawn-like behavior of dolphins, without breathing, is similar to yawning in terrestrial animals, including humans.
 
Résumé
Le bâillement est une action involontaire qui commence par une lente ouverture de la bouche avec inspiration, suivie d'une phase de béance maximale, et se termine par une courte expiration et la fermeture de la bouche. Une grande variété d'espèces de vertébrés, y compris les humains, bâillent. Ici, nous rapportons un comportement de type bâillement sous-marin chez trois grands dauphins communs en captivité, déduit de 119 heures d'observations. Cinq cas de comportement ressemblant à un bâillement ont été sélectionnés sur 2045 comportements bouche ouverte, après avoir supprimé les comportements bouche ouverte intentionnelle. Des comportements de type bâillement ont été choisis avec un rapport de durée d'ouverture-fermeture de la bouche 1 (durée de la phase 3, la période de fermeture de la bouche après l'ouverture maximale, divisée par la durée de la phase 1, la période d'ouverture de la bouche du début au maximum ouverture). Des évaluateurs humains naïfs ont sélectionné des comportements « semblables à des bâillements ». Les cinq cas de comportement ressemblant à un bâillement se sont produits pendant des périodes d'inactivité, similaires aux bâillements humains. Dans trois des cinq cas, les niveaux d'inactivité ont diminué de manière significative dans les 4 minutes suivant le comportement semblable à un bâillement ; par conséquent, un comportement semblable à un bâillement chez les dauphins peut augmenter leur niveau d'excitation dans les états de somnolence. Ainsi, le comportement semblable au bâillement des dauphins, sans respirer, est similaire au bâillement des animaux terrestres, y compris les humains.
 
To the best of our knowledge, this is the first study to examine un- derwater open-mouth behaviors that might be classified as yawning in dolphins. The yawning action of the mouth has been widely identified among various vertebrates (e.g., Sauer and Sauer, 1967; Luttenberger, 1973; Baenninger, 1987; Miller et al., 2010; Bakkegard, 2017) but has yet to be confirmed in a fully aquatic mammal.
 
Do dolphins really yawn?
 
Yawning is characterized by a wide, open mouth, accompanied by deep inhalation, with a three-phase structure. Yawning in animals, including humans, is generally subjectively judged by a researcher, based on the appearance of the behavior (e.g., Gallup, 2011), but an OCDR 1 is one of the quantitative characteristics of yawning (Reiss- land et al., 2012). The yawn-like behaviors observed in these common bottlenose dolphin are similar to yawning in animals in terms of their behavioral structure (three phases with OCDR 1 and maximum gape). Additionally, these yawn-like behaviors occur during resting states, and possibly function in awakening from drowsy states, which seems to be similar to the arousal hypothesis for the function of yawning (Guggis- berg et al., 2010; Walusinski, 2006). These results imply that the yawn-like behavior observed in these common bottlenose dolphin is yawning.
 
The three-phase structures with OCDR 1 of the yawn-like behavior in dolphins are quite similar to yawning in human fetuses (Reissland et al., 2012) and other animals [e.g., old-world monkeys, South Amer- ican sea lions (Otaria flavescens), and Red Hills salamanders] (Deputte, 1994; Bakkegard, 2017; Palagi et al., 2019). Traditionally, yawning in animals has been extracted as yawn-like open-mouth behavior using only the visual impression of a researcher (on-site or recorded video) (e. g., on-site: Deputte, 1994, recorded video: Palagi et al., 2019). Our method here was conservatively double-checked; first, the first author extracted the yawn-like behaviors by visual inspection, and then 10 nai_ve evaluators selected the yawn-like behaviors from open-mouth behaviors with similar durations and OCDR 1. This double-checked inspection resulted in five agreements and two disagreements in yawn-like behaviors between the first author's selection and the selection of the 10 evaluators. The maximum gape should be added to quantitatively select yawn-like behaviors because, in the two disagreements, the first-author-selected "yawn-like" behaviors that both had "medium" gapes instead of "large" gapes.
 
Several mammals (e.g., primates, lions, and South American sea lions), including humans, yawn frequently in drowsy states (Deputte, 1994; Baenninger, 1987; Palagi et al., 2019). The yawn-like behaviors observed in these common bottlenose dolphin also occurred when in a resting state, or during sleepy or drowsy states which required arousal. Further research is needed to investigate whether these yawn-like behaviors are affected by circadian rhythms, like human yawns (Zilli et al., 2007).
 
Inactivity levels decreased within a few minutes of yawn-like behavior in these common bottlenose dolphin, after which they stabilized in a resting state. Yawn-like behavior in dolphins seemed to trigger arousal and change the state of inactivity. This observation fits the arousal hypothesis of human yawning, in which yawning is thought to induce arousal. Moreover, in previous studies yawning in other mammals, including long-tailed macaques (Macaca fascicularis), gray-cheeked mangabeys (Lophocebus albigena), and African elephants (Lox- odonta africana), has been shown to function in arousal (Deputte, 1994; Rossman et al., 2017).
 
The existence of yawning without breathing in cetaceans as well as in human and rat fetuses requires the definition of yawning (a wide, open mouth with deep inhalation) to be broadened. We propose the definition of animal yawning be amended as follows: "Yawning is an involuntary action that starts with slow mouth opening, followed by a maximum gaping phase, and ends with rapid closing of the mouth."
 
Categorizing open-mouth behaviors in dolphins We propose the following steps to distinguish yawning from other open-mouth behaviors in fully aquatic mammals: 1) record all open- mouth behaviors, 2) select open-mouth behaviors with sufficiently long durations to classify the three phases (0.3 s for the common bottlenose dolphin) and without obvious purpose, and 3) select open- mouth behaviors with three clear phases, an OCDR 1, and with maximum mouth size during Phase 2. After these steps have been completed, the remaining open-mouth behaviors could be classified as yawning in fully aquatic mammals.
 
Yawning frequency across taxa
 
Yawning in these common bottlenose dolphin and other mammals, including humans, differs in the frequency of occurrence. The common bottlenose dolphins in the present study yawned only five times, for a total of 9 s, over 119 h of observation (conservative values) (averaging 0.03 yawns/ind./h). Other mammals yawn more often, for example, lion: 1.2 yawns/ind./h (Baenninger, 1987); mandrill: 0.78 yawn- s/ind./h (Baenninger, 1987); Przewalski's horse (Equus ferus prze- walskii): 0.94 ± 0.89 yawns/ind./h (Gorecka-Bruzda et al., 2016); and the domestic horse (E. caballus): 0.68 ± 0.86 yawns/ind./h (Goreck a-Bruzda et al., 2016). Yawning in the common bottlenose dolphin thus seems to be a rare behavior compared to other mammals. This difference could be related to their fully aquatic adaptations and/or other unknown reasons. Further studies are required to clarify why dolphins rarely yawn. Yawning studies on other fully aquatic mammals, such as sirenians, may reveal the effects aquatic adaptations on the frequency of yawning.
 
We did not investigate the relationships between yawn-like behaviors and feeding, or yawn-like behaviors in a socially stressful context. Previous studies have tested whether yawning increases with fixed feeding time in domestic horses (Fureix et al., 2011), lions, and mandrills (Baenninger, 1987), and indicates that yawning before a fixed feeding time might be food-anticipatory yawning (Holmgren et al., 1991). Our subject dolphins, however, did not have fixed feeding times, and the interval between feeding times varied daily, ranging from 2 to 7 h. It was thus difficult to test whether dolphin yawn-like behavior was food-anticipatory yawning. In addition, aggressive behaviors (socially stressful conditions) occurred only once during our observations, which made it impossible to investigate the relationship between yawn-like behaviors and socially stressful conditions. Further research is needed to investigate whether yawn-like behaviors in dolphins are related to feeding or aggressive behaviors.
 
The function of yawning in animals varies, including social reactions when encountering another individual (Siamese fighting fish: Baenninger, 1987), starvation or preparation for feeding (Herman's tortoises and European pond turtles: Luttenberger, 1973, Red Hills salamanders: Bakkegard, 2017, and lions and mandrills: Baenninger, 1987); stress reactions from being handled by a researcher or encountering a predator (budgerigars: Miller et al., 2010); and resting (ostrich: Sauer and Sauer, 1967, this study). Although the contexts of yawning are different, the behavioral form of yawning (slow gaping and quick closure) is similar among various vertebrates, suggesting a stereotyped action pattern (Gallup et al., 2016). Gallup et al. (2016) showed that yawn duration is correlated with brain weight and cortical neuron number in various terrestrial mammals. Further studies on aquatic mammals, as well as other terrestrial animals, will further reveal the evolutionary pathway and function of yawning in animals.