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- mise à jour
du
- 21 janvier
2024
- Sci
Rep
- Jan
7;14(1):361
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- The
sound of yawns makes gelada yawn
- Pedruzzi L, Francescono M, Palagi E,
Lemasson A
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- Tous
les articles sur la contagion du
bâillement
- All
articles about contagious
yawning
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- Abstract
- Yawning is undeniably contagious and hard to
resist. Interestingly, in our species, even the
mere sound of a yawn can trigger this contagious
response, especially when the yawner is someone
familiar. Together with humans, one other mammal
species is known to produce loud and distinct
vocalisations while yawning, Theropithecus
gelada. Geladas are known for their complex
social interactions and rich vocal
communication, making them intriguing subjects
for studying yawning behaviour. To explore the
contagious effect of yawn sounds on geladas, the
authors conducted playback experiments in a
zoo-housed colony with animals living in two
groups. They exposed them to yawn sounds (Test)
or affiliative grunts (Control) produced by
males from either their own group or the other
one. The results were remarkable, as simply
hearing yawn sounds led to yawn contagion in
geladas, with multiple responses observed when
the yawns came from members of their own group.
This finding adds a significant contribution to
the research on mimicry and behavioural
contagion in primates. Moreover, it raises
intriguing questions about the involvement of
sensory modalities beyond visual perception in
these phenomena.
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- Résumé
- Le bâillement est
indéniablement contagieux et il est
difficile d'y résister. Il est
intéressant de noter que, dans notre
espèce, le simple son d'un
bâillement peut déclencher cette
réplication, en particulier lorsque le
bâilleur est quelqu'un de familier. Outre
l'homme, une autre espèce de
mammifère est connue pour produire des
vocalisations fortes et distinctes en
bâillant : Theropithecus gelada. Les
géladas sont connus pour leurs
interactions sociales complexes et la richesse
de leur communication vocale, ce qui en fait des
sujets intrigants pour l'étude du
bâillement. Pour étudier l'effet
contagieux des sons de bâillement sur les
géladas, les auteurs ont mené des
expériences dans une colonie
hébergée dans un zoo, où
les animaux vivaient en deux groupes. Ils les
ont exposés à des
bâillements (Test) ou à des
grognements d'affiliation (Contrôle)
produits par des mâles de leur propre
groupe ou de l'autre groupe. Les
résultats ont été
remarquables, car le simple fait d'entendre des
sons de bâillement a entraîné
la contagion des bâillements chez les
géladas, avec des réponses
multiples observées lorsque les
bâillements provenaient de membres de leur
propre groupe. Cette découverte apporte
une contribution importante à la
recherche sur le mimétisme et la
contagion comportementale chez les primates. En
outre, elle soulève des questions
intéressantes sur l'implication de
modalités sensorielles autres que la
perception visuelle dans ces
phénomènes.
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- Introduction
- Yawning makes you yawn, we have all
experienced that. The phenomenon of yawn
contagion (YC) is not restricted to humans and
seem present mostly in highly social species,
across the primate lineage (great apes1,
cercopithecines, recently in a south American
monkey5 and in a lemur species) as well as in
species from other orders (e.g., pigs, wolves,
domestic dogs, lions, spotted hyenas, African
painted dogs, budgerigars). Despite the
mysteries around the possible functions and
neurobiology underpinning YC, recent findings
suggest that the phenomenon could have evolved
to promote group synchronization10 and that it
correlates to a certain extent with social
closeness. For humans, the phenomenon seems
exaggerated as even just hearing someone yawning
can elicit YC, with this getting easier when the
yawners are familiar.
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- Vocalized yawns are not restricted to
humans; indeed, another mammal species,
Theropithecus gelada, also emits evident
vocalizations while yawning. The gelada is an
Ethiopian endemic monkey species living in
multi-level societies (e.g., units, teams,
bands, communities). The core unit of gelada
groups can be either the one-male unit, composed
of a reproductive adult male, adult females,
their offspring, and eventually one or more
follower males, or the all-male unit, where
subadult or young adult males gather after
dispersion from the natal unit. Moreover, the
species show fission&endash;fusion dynamics
between the different one-male and all-male
group units. Among primates, geladas are
particularly well known for their social
complexity and rich vocal communication. Indeed,
when compared to phylogenetically close taxa
(e.g., Papio and Lophocebus genera), they are
characterized by a relatively richer vocal
repertoire, including their own derived sound
types, and they have often been compared to our
species, not only for their social18, but also
for their communicative complexity.
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- A similar evolutionary social landscape,
with similar challenges (e.g., need of group
coordination with subjects not always in visual
contact), has indeed possibly led to the
emergence of multimodal communication in both
species. In geladas, the acoustic component of
yawns is not a mere by-product of the
inhalation/exhalation cycle but it represents a
distinct vocalisation which is mainly produced
by males. Vocalised yawns represent a
conspicuous signal often audible at notable
distances for their loudness (e.g.,_>_40 m),
further hinting at a possible role of yawning in
communication and coordination. In this
framework, these peculiar vocalisations could
thus be a social outcome of the convergent
evolution experienced by humans and geladas,
both characterised by derived acoustic
repertoires. Although we know that geladas yawn
after seeing others' yawns, we do not know if
the sole acoustic component can elicit
contagion, as little is known about the role
that different sensory modalities play in yawn
contagion and other mimicry phenomena. Among
non-human animals, domestic dogs are known to be
susceptible to human yawn sounds. Yet,
intraspecific auditory YC remains unexplored in
non-human animals. The unique trait of yawn
vocalisation and the analogies with humans
suggest that the vocalisation might have evolved
to make contagion possible also when the
subjects are not in visual contact and thus, we
expected that the sole auditory component could
induce YC. Moreover, as it occurs with human
yawn sounds (human&endash;human YC,
human&endash;dog YC,), we could expect auditory
YC to be modulated according to the degree of
social value of the trigger. Here, to test such
hypotheses we carried out playback experiments
to verify the presence of acoustic-based yawn
contagion in a zoo-housed colony of geladas,
with the animals belonging to two groups housed
in adjacent open enclosures without visual and
acoustic barriers. Specifically, in separate
randomized sessions we exposed the animals to
the sound of yawns (Test) vs affiliative grunts
(Control) produced by in- or outgroup
males.
-
- Discussion
- Through a playback experiment, we made a
noteworthy discovery: auditory yawn contagion
(YC) between conspecifics extends beyond our
species. The mere sound of a yawn can trigger
contagious yawning in geladas. When compared to
control grunts, yawn sounds induced a higher
probability and a greater number of yawns in
both male and female individuals, with similar
contagiousness observed for both the two sexes.
Interestingly, we found that neither
self-directed behaviours (clues of anxiety
states in primates, as described) nor the time
of the day (which generally influences the
frequency of spontaneous yawning) had an impact
on the yawning responses. This is important to
consider, as yawning in primates has often been
associated with anxious or slightly negative
states, potentially leading to non-conclusive
evidence of contagion30. Thus, we ruled out
these possible confounding effects. Regarding
the group membership of the stimulus yawner, we
observed that it did not affect the likelihood
of the yawning response. However, yawn sounds
from individuals within the same group elicited
a higher number of yawns compared to yawn sounds
from individuals outside the group. In agreement
with previous findings on social modulation of
YC based on visual cues, our data extend the
effect of group membership also to YC based on
acoustic cues.
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- The reason behind geladas and humans
producing specific vocalizations while yawning
remains an intriguing puzzle. However, the
unique multimodal nature of this trait suggests
a social function in both species. The finding
that the sole acoustic component can induce yawn
contagion (YC) provides additional evidence for
the behaviour's potential role in regulating
social interactions. Considering the
significance of yawning in group
synchronization, the adaptive value of auditory
YC might be linked to the need for individuals
to maintain acoustic contact when visual contact
is not possible, making this especially relevant
in societies characterized by modularity and
flexibility, and in species with such rich
communicative repertoires. We can only
hypothesize that interdependent causes such as
social complexity, vocal redundance, and
possible adaptive values of auditory YC might
explain the presence of the vocalisation in the
two species. In this context, auditory yawn
contagion could indeed play a crucial role in
intergroup communication and coordination within
gelada multilevel societies, where different
group units are often separated by medium to
long distances. During our analysis of the yawn
responses in the playback experiments, we did
not only consider the presence or absence of
yawning but also the number of yawns produced.
-
- We discovered that yawn sounds produced by
male members of the same group (i.e., more
socially valuable individuals) elicited chains
of more yawns in the responder after its first
yawn, despite the probability of yawn response
being similar when exposed to ingroup or
outgroup yawn sounds. Importantly, here the
interaction Condition*Group in GLMMnumber of
yawns showed that this significant effect was
only present when exposed to yawn stimuli and
not grunts. Indeed, if this result was due to
autocorrelation of yawns (i.e., increased
probability of a second yawn after a first
yawn), we would expect a similar trend
independently from the group membership of the
yawn stimulus once the first yawn has been
evoked in the tested subject. Our findings are
consistent with previous studies that have
demonstrated a social modulation in the
contagiousness of observed or even just heard
yawns (humans, domestic dogs). Notably, in those
studies, yawn contagion was stronger among
socially close group mates or individuals living
together versus those unfamiliar with each
other. In our experiment, all the subjects were
acoustically familiar with each other, as both
groups could see and hear each other but could
not interact (see Methods).
-
- This familiarity led to equally familiar
yawn sounds (eliminating any neophobic effect)
produced by individuals with different social
values (ingroup vs. outgroup). The stronger
contagious response observed towards ingroup
male yawn sounds could potentially trigger a
domino effect, increasing the probability of
other group members perceiving and responding to
previous yawns. In conclusion, our data present
new insights: first, the importance of studying
how the spread of contagious yawns among group
members might lead to synchronizing group
activities, and second, the possibility that, in
such unique species, the acoustic component of
yawns may carry information about the yawner's
identity, allowing conspecifics to recognize the
yawner (in parallel to what might occurs for
domestic dogs with humans). This study adds an
important contribution to the research on the
evolution of mimicry and behavioural contagion
in the primate lineage, prompting further
exploration on the role of sensory modalities
beyond visual perception in these
phenomena.
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