The forked tongue and edge detection in snakes (Crotalus oreganus): An experimental test.

Abstract

Many stimulus-detection systems are lateralized to allow for simultaneous comparison of paired stimuli. It has been hypothesized that the deeply forked tongue of snakes and some derived lizards functions as a chemical edge detector where cues gathered by each tine are kept separate to provide two points of lateral odor assessment by the central nervous system via vomeronasal input. While following a chemical trail, one time can be on the trail, the other off, and such differential information prompts the snake to turn back to the trail. The authors tested this hypothesis in rattlesnakes within a predatory context by unilaterally severing the vomeronasal nerves. If edge detection is used by snakes during prey trailing, then unilateral denervation should disrupt trailing ability. The authors found no change in the seven separate trailing parameters measured. Therefore, they found no support for the edge detection hypothesis as it applies to prey trailing behavior. Instead, the deeply forked tongue may represent a chemosensory specialization to increase odor-sampling area, with snakes and derived lizards detecting only the concentration of chemical trails.

Structural and Functional Characterization of the Tongue and Digestive Tract ofPsammophis sibilans(Squamata, Lamprophiidae): Adaptive Strategies for Foraging and Feeding Behaviors

“…Moreover, it was differentiated and divided into three main distinctive portions such as the apex, body, and root. Our findings were corroborated by several studies that used similar description for tongues in different clades of snakes (Morgans & Heidt, 1978; Mao et al, 1991; Iwasaki & Kumakura, 1994; Iwasaki et al, 1996; Iwasaki & Yoshihara, 2003; Parker et al, 2008). Moreover, the ventral surface of the tongue rests on a pair of lingual plicae.…”

“…In this setting, several rationales were hypothesized explaining the respective role of these plicae in transferring the chemical cues. Previous studies documented that the lingual plicae receive chemical cues and odorant molecules from the tongue tines; however, others stated that the destruction or removal of these plicae did not remarkably impair odor transfer to the VNO (Mcdowell, 1972; Mao et al, 1991; Parker et al, 2008). It was hence plausible that lingual plicae are not necessary to maintain the lateralization of the VNO system (Halpern & Borghjid, 1997).…”

“…In squamates, the tongue primarily functions in food transportation and manipulation (Schwenk, 2000; Iwasaki, 2002), drinking (Jamniczky et al, 2009; Cundall et al, 2012), prey capture (Keiser, 1975; Cooper, 1994), and defensive strategies (Mcdowell, 1972; Bels et al, 1994; Schwenk, 1995). The tongue is also deeply forked (hereafter, bifurcated) and co-opted for chemoreception (Cooper, 1997; Parker et al, 2008; Baeckens et al, 2017 b ) in snakes and some lacertids (De Groot et al, 2004; Herrel et al, 2005).…”

“…During probing action, the tongue darts out of the oral cavity and sweeps its apical tines through the air via oscillatory action; capturing airborne scent molecules and specific chemical cues (Gove, 1979; Schwenk 1993, 1995; Cooper, 1996; Jamniczky et al, 2009; Kaas, 2009; Clark, 2015). The tongue then retracts and transfers chemical cues to a specialized sensory organ in the roof of the buccal cavity, the vomeronasal organ (VNO) (Young, 1990; Graves, 1993; Iwasaki et al, 1996; Parker et al, 2008; Filoramo & Schwenk, 2009). Schwenk (1994 a ) found that the degree of lingual bifurcation is directly linked to foraging behavior; putatively reflecting the extent to which squamates bear forked tongues in relation to the time spent foraging and searching.…”

Efficacy of Milorganite® as a Non-Venomous Snake Repellent (Poster)

“…Chemical sensitivity of the olfactory system in snakes is reported to be the most important sense in prey detection, orientation, and sexual behavior (Muntean et al 2009). The tongue itself may increase odor-sampling area and directly transfer contacted chemical to a highly developed vomeronasal system for analysis (Muntean et al 2009, Parker et al 2008. Based on gene analysis of olfactory receptors, it was predicted that snakes rely heavily on the olfactory receptor system as a method of odor detection (Byerly et al 2010).…”