Morphology and fibre‐type distribution in the tongue of the Pogona vitticeps lizard (Iguania, Agamidae)

Abstract

Agamid lizards use tongue prehension for capturing all types of prey. The purpose of this study was to investigate the functional relationship between tongue structure, both surface and musculature, and function during prey capture in Pogona vitticeps. The lack of a detailed description of the distribution of fibre-types in the tongue muscles in some iguanian lizards has hindered the understanding of the functional morphology of the lizard tongue. Three methodological approaches were used to fill this gap. First, morphological analyses were performed (i) on the tongue surface through scanning electron microscopy, and (ii) on the lingual muscle by histological coloration and histochemistry to identify fibre-typing. Secondly, kinematics of prey capture was quantified by using high-speed video recordings to determine the movement capabilities of the tongue. Finally, electromyography (EMG) was used to identify the motor pattern tongue muscles during prey capture. Morphological and functional data were combined to discuss the functional morphology of the tongue in agamid lizards, in relation to their diet. During tongue protraction, M. genioglossus contracts 420 AE 96 ms before tongue-prey contact. Subsequently, Mm. verticalis and hyoglossus contract throughout tongue protraction and retraction. Significant differences are found between the timing of activity of the protractor muscles between omnivorous agamids (Pogona sp., this study) and insectivorous species (Agama sp.), despite similar tongue and jaw kinematics. The data confirm that specialisation toward a diet which includes more vegetal materials is associated with significant changes in tongue morphology and function. Histoenzymology demonstrates that protractor and retractor muscles differ in fibre composition. The proportion of fast glycolytic fibres is significantly higher in the M. hyoglossus (retractor muscle) than in the M. genioglossus (protractor muscle), and this difference is proposed to be associated with differences in the velocity of tongue protrusion and retraction (5 AE 5 and 40 AE 13 cm s À1 , respectively), similar to Chamaeleonidae. This study provides a way to compare fibre-types and composition in all iguanian and scleroglossan lizards that use tongue prehension to catch prey.

Light and scanning electron microscopy of the tongue of the sand lizard (Lacerta agilis)

“…The epithelium of the dorsal lingual surface is nonkeratinised stratified squamous, as was reported in Anolis carolinensis [18], Scincella tsinlingensis [20], Pogona vitticeps [21], Tarentola annularis [9], Podarcis sicula [3], Iguana iguana [6], Laudakia stellio [16] and Gekko japonicus [11]. This suggests that the occurrence of this type of the lingual epithelium is typical in lizards.…”

“…apex, body and root. Its lingual apex is bifurcated, as has been described in the Iguana iguana [1,6], Podarcis sicula [3], Takydromus tachydromoides [13], Scincella tsinlingensis [20] and Pogona vitticeps [21]. Thus, shaping of the lingual apex can be related to an easier access to the vomeronasal organ.…”

“…Lingual glands were identified in some species of lizards such as Pogona vitticeps [21], Laudakia stellio [16] and Scincella tsinlingensis [20]. Similarly, as in L. agilis, no glands were described in Iguana iguana [6].…”

“…The dorsal surface of the tip of the tongue is smooth in many lizards such as the green anole, Anolis carolinensis [18], blue-tongued skink, Tiliqua scincoides [2], Japanese lizard, Takydromus tachydromoides [13], bearded dragon, Pogona vitticeps [21], Italian lizard, Podarcis sicula [3], rough tailed rock agama, Laudakia stellio [16] and green iguana, Iguana iguana [1,6].…”

“…Cylindriform papillae were distinguished on the dorsal lingual surface in the green anole, Anolis carolinensis [18], blue-tongued skink, Tiliqua scincoides [2], rough tailed rock agama, Laudakia stellio [16], green iguana, Iguana iguana [1,6], Madagascan collared iguana, Oplurus cuvieri [8], Italian lizard, Podarcis sicula [3] and bearded dragon, Pogona vitticeps [21]. Plumose papillae were described in the green anole, Anolis carolinensis [18] and bearded dragon, Pogona vitticeps [21]. The plumose papillae may be important in mastication and deglutition of food [18].…”