A cryptic intermediate in the evolution of chameleon tongue projection

The tongue of Leopard Gecko (Eublepharis macularius): LM, SEM and confocal laser study

The leopard gecko is a crepuscular and insectivorous reptile. The role of the tongue in this reptile is fundamental for the prey capture and ingestion and is not related with eyes cleaning as usual in other geckos. The elongated tongue can be divided into a foretongue with a slightly bifurcated apex and a hindtongue. Scanning electron microscopy demonstrated that several different papillae are present on the dorsal surface, foliate and dome-shaped in the foretongue, becoming thicker and stouter with reduced interpapillary spaces in the lateral parts. The hindtongue is characterised by wide foliate papillae with indented margins and deep fissures of the mucosa. Light microscopy showed the presence of a stratified slightly keratinized squamous epithelium in the apex of the foretongue, a stratified non-keratinized squamous epithelium in the fore and in the hindtongue. In the foretongue, numerous muciparous caliciform cells were observed. Moreover, the presence of taste buds on the tongue ventral surface was demonstrated for the first time in this species and the confocal laser study revealed a strong immunoreactivity for the S-100 protein in the sensory cells. Therefore, the results obtained could give a contribution to the knowledge of the tongue anatomy and are a basis for eventual further studies regarding the feeding habits in a reptile become a popular pet.

EVOLUTION OF PUFFERFISH INFLATION BEHAVIOR

The evolution of the extraordinary inflation mechanism of pufferfishes was studied in the light of an independently derived phylogenetic hypothesis of tetraodontiform fishes. Inflation behavior is found in all members of the puffer sister taxa Tetraodontidae and Diodontidae. However, most other tetraodontiform fishes exhibit two functionally similar behaviors. All taxa exhibit a "coughing" behavior and, with the exception of the sister-group to all other tetraodontiforms, represented by the Triacanthidae, all lineages "blow" strong jets of water out of their mouth to excavate prey. Functional specializations associated with the three behaviors were identified from anatomical analyses and electromyographic recordings of muscle activity in representatives of the major lineages of the order. The phylogenetic distribution of the three buccal compression behaviors and their functional bases indicates the following: (1) the evolution of inflation behavior involved major structural modifications of the head that function in a novel mechanism that links depression of the floor of the mouth to posterior expansion of the buccal cavity; (2) the contraction patterns of four key head muscles used in the three behaviors are generally similar both across behaviors and taxa; (3) however, the distribution of the two significant modifications of muscle activity are consistent with the hypothesis that the three behaviors represent a transformation series from coughing to water blowing to inflation. The motor pattern for water blowing is a slightly modified version of that seen in coughing, and the inflation motor pattern retains the blowing specialization and adds a single additional modification. The convergent evolution of a poorly developed inflation behavior in at least one genus of filefish provides evidence that tetraodontiform fishes are predisposed to the evolution of this unusual defensive behavior. The presence of a well developed water-blowing behavior in most tetraodontiform lineages may represent an intermediate functional specialization that increased the probability of the evolution of inflation.

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

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 ± 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 ± 5 and 40 ± 13 cm s(-1) , 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.

Morphology of the lingual dorsal surface and oral taste buds in Italian lizard (Podarcis sicula)

The Italian lizard (Podarcis sicula) is the most diffused reptile in Italy, but it is also present in other European countries. This lizard belongs to the Lacertidae family, lives near walls, slants and along the borders of the paths; its diet includes bugs and aracnids. No data are so far available in literature about the three-dimensional morphology of the tongue of Podarcis sicula, therefore the aim of the present paper was to study by scanning electron and light microscopy the three-dimensional characteristics of the dorsal lingual surface and moreover the presence of chemosensory receptors like the taste buds in the oral cavity. Our results demonstrate that the Podarcis sicula tongue is a triangular muscular membranous organ, dorsoventrally flattened and that three different areas can be observed: a bifid apex, a body and a root. No papillae were observed in the apex, characterized by a flattened mucosa and by two deep median pouches. In the body cylindrical papillae with a flat surface are present, aborally gradually substituted by imbricated papillae. Foliate-like papillae were observed in the lateral parts of the tongue body. No sensory structures were showed on the lingual dorsal surface, while they were numerous in the oral cavity, particularly on the gingival epithelium. The light microscopy shows, on the dorsal surface, a stratified pavimentous not keratinized epithelium, conversely keratinized along the ventral surface. Many caliciform cells on the lateral parts of the papillae, deputed to the secretion of mucus, were also observed. Therefore, the results obtained in this paper could give a contribution to the knowledge of the tongue anatomy in a species widely diffused in different European countries and could be of help for clinical purposes in reptiles.

Functional morphology of feeding in the scale-eating specialistCatoprion mento

The wimple piranha, Catoprion mento, has a narrow-range natural diet with fish scales comprising an important proportion of its total food intake. Scales are eaten throughout most of ontogeny and adults feed almost exclusively on this food source. Catoprion exhibits a novel prey capture behavior when removing scales for ingestion. Scale feeding strikes involve a high-speed, open-mouth, ramming attack where the prey is bitten to remove scales and the force of the collision knocks scales free. Unique kinematic parameters of scale-feeding strikes include a mean gape angle of nearly 120° and a `plateau' stage of prolonged maximum displacement for cranial elevation and opercular expansion. When feeding on live fish or loose scales, Catoprion performs a typical ram/suction attack that is modulated according to the elusiveness of the prey. Captures of elusive fish elicit faster strikes with greater displacement of cranial elements than do attacks on loose scales sinking in the water column. Despite its specialized diet and suite of anatomical characters, functional versatility in feeding behavior has not been reduced in Catoprion, as predicted by many analogous studies in functional morphology. On the contrary, the behavioral repertoire of Catoprion has been broadened by the addition of a novel behavior for scale feeding.

Feeding behavior modulation in the leopard lizard (Gambelia wislizenii): Effects of noxious versus innocuous prey

Feeding, a fundamentally rhythmic behavior in many animals, is expected to exhibit modulation with respect to prey type. Using high-speed videography (200 frames(-1)) and kinematic analysis, we investigated prey-processing behavior in the long-nosed leopard lizard (Gambelia wislizenii). The effects of two prey types were examined, innocuous immature crickets (Acheta domesticus) and noxious stinging hymenopterans (honeybees [Apis mellifer] and yellow jackets [Vespula sp.]). Stinging hymenopterans are processed more extensively, with higher gape-cycling frequencies, and for a greater duration than are crickets. Generalized tetrapod feeding models were used as a framework to test the hypothesis that gape profile characteristics are modulated in response to prey noxiousness. Cricket processing generally fits the models, but hymenopteran processing departs from typical model parameters. In particular, the SO phase is absent to barely detectable during hymenopteran processing. This likely represents an effect of extrinsic neural input on a centrally directed rhythmic motor pattern, possibly to avoid being stung. Differences in the capture behavior of crickets versus hymenopterans indicate that G. wislizenii assesses prey noxiousness before physical contact with prey and modifies its capture behavior accordingly. These results add to the growing body of evidence that sensory information can play a critical role in shaping stereotyped rhythmic behaviors in non-mammalian tetrapods.

Comparative study of the innervation patterns of the hyobranchial musculature in three iguanian lizards: Sceloporus undulatus, Pseudotrapelus sinaitus, and Chamaeleo jacksonii

The neuroanatomy and musculature of the hyobranchial system was studied in three species of iguanian lizards: Sceloporus undulatus, Pseudotrapelus sinaitus, and Chamaeleo jacksonii. The goal of this study was to describe and compare the innervation and arrangement of the hyobranchial musculature in the context of its function during tongue protrusion. A comparison of the hyobranchial innervation patterns revealed a relatively conserved innervation pattern in S. undulatus and P. sinaitus, and a modified version of this basic layout in C. jacksonii. All three species show anastomoses between sensory neurons of the trigeminal nerve and motor neurons of the hypoglossal nerve, suggesting that feedback may be important in coordinating tongue, jaw, and hyoid movements. The hyobranchial musculature of S. undulatus is very similar to that of P. sinaitus; however, there are minor differences, including the presence of an M. genioglossus internus (GGI) muscle in S. undulatus. Further differences are found mainly in functional aspects of the hyobranchial musculature, such as changes in the muscle lengths and the origins and insertions of the muscles. In C. jacksonii the hyobranchial system is comprised of largely the same components, but it has become highly modified compared to the other two species. Based on the innervation and morphological data gathered here, we propose a revision of the terminology for the hyobranchial musculature in iguanian lizards.

Comparative study of tongue protrusion in three iguanian lizards, Sceloporus undulatus, Pseudotrapelus sinaitus and Chamaeleo jacksonii

The goal of this study was to investigate the function of the hyolingual muscles used during tongue protraction in iguanian lizards. High-speed videography and nerve-transection techniques were used to study prey capture in the iguanid Sceloporus undulatus, the agamid Pseudoptrapelus sinaitus and the chameleonid Chamaeleo jacksonii. Denervation of the mandibulohyoideus muscle slips had an effect only on P. sinaitus and C. jacksonii, in which tongue protrusion or projection distance was reduced. In C. jacksonii, denervation of the M. mandibulohyoideus completely prevented little hyoid protraction. Denervation of the M. verticalis had no effect on S. undulatus, but reduced tongue protrusion distance in P. sinaitus. Denervation of the accelerator muscle in C. jacksonii inhibited tongue projection completely. The function of the M. mandibulohyoideus and M. verticalis has become increasingly specialized in P. sinaitus and especially in C. jacksonii to allow greater tongue protrusion. The combined results of these treatments suggest that these three groups represent transitional forms, both morphologically and functionally, in the development of a projectile tongue.

Feeding kinematics of phelsuma madagascariensis (Reptilia: gekkonidae): testing differences between iguania and scleroglossa

The kinematics of feeding in the gekkotan lizard Phelsuma madagascariensis (Scleroglossa) was investigated using high-speed cinematography (200–300 frames s(−)(1)) and X-ray films (64 frames s(−)(1)). Qualitative kinematic analysis of the head and jaw displacement of the prey to (capture) and within (reduction, transport, swallowing, licking) the buccal cavity are compared for two types of prey (crickets and mealworms) in 30 feeding sequences from four individuals. Maximal displacement of structures and timing of events are compared statistically to assess the differences among the phases and the prey using analysis of variance. P. madagascariensis uses its jaws only to capture the two types of prey item, and the capture jaw cycle is divided into fast-opening (FO), fast-closing (FC) and slow-closing (SC) stages only. As in iguanians and other scleroglossans, the reduction and transport cycles always involve a slow opening (SOI and SOII) stage before the FO stage, followed by FC and SC stages: this last stage was not easily identified in all feeding phase. Transport of the prey was followed by a large number of licking cycles. Our data show (i) that the capture profile in gekkotans is similar to that observed for other scleroglossans and different from that described for iguanians (e.g. the absence of an SO stage); (ii) that the kinematics of jaw and related hyo-lingual cycles of intraoral manipulation (reduction and transport) are similar in lizards with a very different hyo-lingual system (Iguania, Gekkota and Scincomorpha), suggesting a basic mechanism of feeding cycles in squamates, transformed in varanids and snakes; and (iii) that prey type affects the kinematics of capture and manipulation, although the high level of variation among lizards suggests a possible individual modulation of feeding mechanism. A principal components analysis was performed to compare capture and transport cycles in this study of P. madagascariensis (Gekkota) and a previous study of Oplurus cuvieri (Iguania). This analysis separated the capture cycle of each species, but the transport cycles were not completely separated. These results demonstrate the complexity of the modulation and evolution of feeding process in squamates.

Tongue structure and function in Oplurus cuvieri (Reptilia: Iguanidae)

The anatomy of the hyo-lingual apparatus in the iguanid lizard Oplurus cuvieri has been studied by light microscopy and scanning electron microscopy. Four areas were observed on the dorsal lingual epithelium of the lizard. Tongue tips are covered with a smooth epithelium. Closely packed flattened and cylindriform papillae cover the foretongue. The surface of the midtongue bears an unpapillose epithelium. Short conical papillae are arranged on the two lateral posterior bundles of the tongue. At high magnification, microvilli and microridges are widely distributed over the surface of the papillae. The epithelium of the papillae is composed of cells filled with secretory granules. Each surface plays successive roles during food ingestion, intra-buccal transport, and swallowing. The mucous interpapillary spaces would serve the adherence between the tongue and the food, the smooth epithelium of the midtongue should facilitate movements of the prey toward the pharynx, and conical papillae of the hindtongue present a rough surface which should act on the prey during the swallowing phase. The intrinsic morphology of the tongue is rather similar to that previously described for iguanids, but fibers of M. verticalis encircles ventrally the lingual process. These fibers could act in tongue protrusion as previously suggested for agamids. The morphology and function of the extrinsic tongue musculature and the hyoid musculature, analysed by electrical stimulations, are similar to the previous descriptions in iguanids and agamids either for feeding or displaying functions.

Kinematics of prey capture and chewing in the lizard Agama agama (squamata: Agamidae)

High speed video recordings (200 fields per second) of prey capture and food processing in Agama agama permit the identification of strikes, chews and transport movements. Ten variables from strike movements and seven variables from chewing sequences are digitized; transport movements are inspected only. Univariate and multivariate statistical analyses disclose significant interindividual differences for three variables (maximum gape distance, maximum head angle, and maximum throat distance); but neither these nor principal components analysis show differences between strikes and chews for any of the gape change and hyoid depression variables. However, strikes and chews obviously differ in tongue protrusion and body movements. Chewing may be divided into four stages, comparable to those of transport cycles of other lizards and the generalized tetrapod model. Transport differs from chewing by having a shorter power stroke and relatively more cranial and less jaw movement. The kinematics of feeding in Agama agama are compared with those of other lizards studied previously.