Buccal Expansion during Hissing in the Puff Adder, Bitis arietans
Copeia (Impact Factor: 1.03). 02/2001; 2001(1):270-273. DOI: 10.1643/0045-8511(2001)001[0270:BEDHIT]2.0.CO;2
Videoradiographic analyses were made of hissing in puff adders (Bitis arietans). During the hiss the larynx remains relatively stationary immediately adjacent to the internal nares. The exhalatory portion of the hiss is characterized by a distinct expansion of the caudal buccal cavity, including a depression of the hyoid and di-vergence of the cornua. This buccal expansion is hypothesized to be an epiphenom-enon of intraoral pressure generated by the exhalatory airstream of the hiss. E XPANSION of the body, particularly the an-terior portion, is a common feature of the defensive repertoire of snakes (for reviews see Mertens, 1946; Carpenter and Ferguson, 1977; Greene, 1988). These localized body expansions may be horizontal (such as ''hooding'' in Naja; Young and Kardong, 1989) or vertical (such as throat expansion in Ptyas mucosus; Young et al., 1999a); the plane of expansion generally cor-relates with the main visual axis of the potential predator (Greene, 1979; Senter, 1999). Al-though many snakes use respiratory mecha-nisms for generalized body expansion (e.g., Kin-ney et al., 1998; Young et al., 1999b), the spe-cialized defensive displays appear to result from differential contributions of the cranial ribs and the anterior portion of the respiratory tract (Young et al., 2000). The specializations of the anterior respiratory tract, which produce defensive visual displays, may also result in unusual acoustic properties (Young, 1991b; Young et al., 1999a). Most de-fensive sounds produced by snakes have a sim-ple acoustic structure characterized by very low levels of frequency and amplitude modulation and little or no temporal patterning (Young, 1997, 1998b). Many snakes such as Heterodon pla-tyrhinos (Young and Lalor, 1998) and Daboia rus-selii (Young, 1998a) are obligate nasal hissers in which the exhalent airstream is always passed through the internal nares. Experimental anal-yses of hissing in another obligate nasal hisser, the puff adder (Bitis arietans), revealed that the larynx plays a passive role during sound pro-duction, remaining patent throughout the sound-producing portions of the hissing cycle (Young et al., 1999b). The larynx of snakes is structurally simple (Kardong, 1972a,b; Young, 2000) and with the exception of Pituophis melanoleucus (Young et al., 1995) shows few anatomical specializations. Changes in the relative position of the larynx within the oral cavity during the hiss and/or changes in the dimensions of the buccal cavity itself could result in a resonance effect and a visible distension of the buccal cavity similar to what has been described as a defensive display in Psammophis (Werner, 1985). Recent studies using cineradiography and videoradiography on squamates have provided documentation of in-trabuccal processes relating to chemosensory searching (Young, 1990, 1991a), defensive dis-plays (Bels et al., 1995), prey transport and swal-lowing (Janoo and Gasc, 1992; Cundall, 1995; Kley and Brainerd, 1996), drinking (Bels and Kardong, 1995), and ventilation (Owerkowicz et al., 1999). In this study, we used videoradiogra-phy to study intrabuccal processes associated with defensive displays in the puff adder, B. ar-ietans.
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ABSTRACT: Snakes are frequently described in both popular and technical literature as either deaf or able to perceive only groundborne vibrations. Physiological studies have shown that snakes are actually most sensitive to airborne vibrations. Snakes are able to detect both airborne and groundborne vibrations using their body surface (termed somatic hearing) as well as from their inner ears. The central auditory pathways for these two modes of "hearing" remain unknown. Recent experimental evidence has shown that snakes can respond behaviorally to both airborne and groundborne vibrations. The ability of snakes to contextualize the sounds and respond with consistent predatory or defensive behaviors suggests that auditory stimuli may play a larger role in the behavioral ecology of snakes than was previously realized. Snakes produce sounds in a variety of ways, and there appear to be multiple acoustic Batesian mimicry complexes among snakes. Analyses of the proclivity for sound production and the acoustics of the sounds produced within a habitat or phylogeny specific context may provide insights into the behavioral ecology of snakes. The relatively low information content in the sounds produced by snakes suggests that these sounds are not suitable for intraspecific communication. Nevertheless, given the diversity of habitats in which snakes are found, and their dual auditory pathways, some form of intraspecific acoustic communication may exist in some species.