mystery of yawning
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Le bâillement : de l'éthologie à la médecine clinique
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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
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21 septembre 2012
Marine and Freshwater
Behaviour and Physiology
2008;41(3):161-167
Mouth gaping behavior
in Caribbean reef sharks, Carcharhinus perezi
Erich Kurt Ritter
Shark Research Institute, Princeton, NJ, USA

Chat-logomini

 
Baillements des poissons - Fish's yawn
 
Mouth gaping in sharks has been considered to be either a threat display or a response to sharksucker irritation, but has never been examined in greater detail. Another form of gaping was observed frequently around feeding scenarios, primarily when sharks swam away from the food source.
 
This form of a yawn-like behavior of Caribbean reef sharks, Carcharhinus perezi, was videotaped during both standard feeding and non-feeding scenarios, and examined for both proximate causation and function. This type of gaping reflects a simulated bite process, including all bite phases, but differs from actual bites in that the duration is as great as 10 times longer, with the expansion phase disproportionally prolonged and a pause at the gape's peak. Of all the possible functions discussed, a maintenance behavior.
 
 
 
Introduction
 
Varying forms of gaping have been observed among all classes of vertebrates and can appear as responses to physiological functions, such as respiration (Greco et al. 1993; Baenninger 1997; Walusinki 2006), expressions of comfort or discomfort (Henry and Atchison 1979; Hadidian 1980; Mearns 1989), and communication (e.g., Smith 1999; Steinhart et al. 2005). For sharks, it was suggested to be either a reaction to sharksucker irritation and labeled as ''yawning'' (Ritter 2003) or part of a threat display (Ritter and Godknecht 2000; Martin 2007) and simply called ''gaping.'' Neither suggestion has been thoroughly examined in sharks as ''yawning'' simply refers to an extended mouth opening that is analogous to terrestrial animals, and ''gaping'' refers to a threat display without further clarification.
 
During feeding experiments with Caribbean reef sharks, Carcharhinus perezi, gaping has also been noted after feeding (Ritter 2001). Such gaping behavior is executed slowly, entailing all bite phases (Motta et al. 1997), and most often includes upper jaw protrusion (e.g., Wilga et al. 2001). The main objective of this study was to further understand this type of jaw opening with a special emphasis on both proximate causation and function.
 
(...)
 
Discussion
 
All regular kinematic biting phases are exhibited during the presented gaping behavior with two major differences: (1) an approximate 10 times longer overall duration when compared with regular bites of C. perezi and other carcharhinid species (Motta 2004), and (2) a motion freeze between 0.2 and 0.3 seconds at the mouth opening's peak. While Motta (2004) established that the average time of expansion was 26% of an overall bite duration for comparable carcharhinid species, the same phase during these gapes for C. perezi was close to twice that for protruding gapes, and even longer for non-protruding gapes. This observation indicates that slow opening appears to be of importance during gape behavior. Probable causes for this gaping behavior are likely feeding related, indicated by (1) the immediate drop of the gape rate by more than 72% after the food was consumed, despite shark density being reduced by only 18%, (2) the high occurrence of gaping ( 98%) when the sharks swam away from the food source, and (3) the lack of other distinctive behaviors that could have triggered this form of mouth opening. In order to tear off a piece of the offered food source, a shark had to first gouge it. Gouging is very complex biomechanically where jaw elements are pulled from their seats or resting positions when biting into the food and are later repositioned when the bite is completed (e.g., Motta et al. 1997; Wilga and Motta 1998).
 
During such motions, especially after extended tearing, which is often observed at the offered food source, it is likely that certain jaw elements may not be repositioned properly after the bite's execution, and gaping could then function as a maintenance response. Prolonged expansion could assist in slowly pulling the jaw elements once more from their resting positions before repositioning them into their appropriate places. A possible mis-repositioned element could be the hyomandibula, with attachments to the neurocranium and jaw, or the upper jaw itself, with its orbital processes that fit into the cranial seats when in a resting position (Frazzetta and Prange 1987; Compagno 1988; Motta and Wilga 2001). Although it could be argued that the involved ligaments and muscles that connect the upper jaw and the cranium ought to prevent dislocation of the upper jaw (e.g., Wilga et al. 2001), protrusion per se is a form of dislocation since the upper jaw elements are pulled from their seats, and, hence, proper retraction could fail occasionally. If indeed this simulated, non-feeding biting behavior functions as a maintenance behavior, then non-protruding gapes would merely reflect a stretching process, similar to the yawning function in snakes (e.g., Graves and Duvall 1983).
 
Six sharks exhibited double-gaping behavior. The most distinctive difference compared with single gapes was that the second gapes were executed significantly faster with a more than twofold increase in speed. However, the first gapes exhibited the same duration for all phases as the single gapes. In addition, two sharks yawned with their heads and rolled their bodies during their second gape. It could be postulated that a speed increase, together with an additional head and body motion, also acts as a stretching response for the mouth area and, hence, further contributes to a proper repositioning after an initial failed gape. Although the low number of double-gapes is not representative, it could imply that these simulated, non-feeding biting behaviors per se have a high rate of correct repositioning, and double-gapes are more of an exception.
 
Gaping could also function as a cleaning response. Food is moved through the buccal cavity by the interactions between head, jaw, and gill movements in an anterior to posterior direction (e.g., Wilga et al. 2001), and food particles could potentially become wedged in the gill area. An increased volume of water, enabled through gaping, would increase water pressure through the buccal cavity and gill area when the mouth is closing, thereby freeing these particles. Although food particles were never seen emerging from the gill slits after gaping occurred, it is possible that they were swallowed.
 
Throughout the vertebrates, gapings are exhibited for a variety of reasons. In addition to being a maintenance behavior (e.g., Hadidian 1980), gaping behavior can also reflect stress or threat (e.g., Baenninger 1987), an arousal response (e.g., Walusinski 2006), or the well-known physiological response to a lack of oxygen (e.g., Kita et al. 2000). Although post-prandial effects in sharks after feeding have occurred (Papastamatiou 2007; Papastamatiou et al. 2007), increased oxygen demands did not create such responses in these studies. However, it was hypothesized (Baenninger 1987) that teleosts may yawn prior to metabolically demanding events such as feeding. Tricas' (1982) anecdotal observation that sharks yawned prior to consuming prey could support this hypothesis; however, a single yawn to compensate for an upcoming lack of oxygen seems unlikely for sharks.
 
Among sharks, gaping has been linked to threat display (e.g., Martin 2007) but that form of gaping is always executed very quickly with only a partial mouth opening and without upper jaw protrusion. If the presented form of gaping indeed were to reflect a threat display, it would primarily occur when approaching a food source to intimidate nearby sharks and not when swimming away, as happened with 98% of the gapes observed. This assumption would also be true for a possible stress display. Similarly, during non-feeding dives, no other sharks were commonly present when gaping occurred, and the observation area was unobstructed without the possibility that a shark was cornered or hindered in any other way that could have triggered a stress response. Considering all the parameters measured in this study, maintenance behavior appears to be the most likely explanation for the gaping behavior. Nevertheless, further study should investigate which of the upper jaw elements can be pulled from their resting position to such an extent that correct repositioning might
 
Bioelectric-mediated predation by Swell Sharks, Cephaloscyllium Ventriosum Tricas T. Copeia.1982;4:948-952