Macroscopic, microscopic, and immunofluorescent characterization of the Greek tortoise (Testudo graeca graeca) oropharyngeal floor with concern to its feed adaptation as a herbivorous land reptile

The current investigation focuses on gross anatomy, light, and scanning electron microscopy (SEM) of the Testudo graeca oropharyngeal floor, with particular reference to the immunofluorescence technique to examine its tongue. The T. graeca oropharyngeal floor showed many anatomical structures: the lower rhamphotheca, paralingual ridge, lower alveolar ridge, tongue, laryngeal mound, and glottis. The lower rhamphotheca appeared as a V-shaped jaw line with a highly serrated edge and a median tomium (beak). SEM observations of the lingual apex and the lingual body showed rectangular and conical filiform papillae with porous surfaces and taste pores. Meanwhile, the lingual root had two wings that carried papillae with different shapes: dagger-shaped, conical, bifurcated, and leaf-like papillae, and these papillae lacked taste pores. The laryngeal mound had openings for the laryngeal mucus gland and its secretions. Light microscopy findings showed mucous glands in the propria submucosa and near the mucosal surface of the lingual apex. The lingual root had lingual papillae and two hyaline cartilaginous skeletons between skeletal muscles, and the lingual papillae were elongated filiform, rectangular filiform papillae, and fungiform papillae. The lamina propria constituted the core of the lingual papillae and the mucous gland, they had a positive reaction with the periodic acid schiff (PAS) reagent. The apical surface of the fungiform papillae had taste pores. Under immunofluorescence, the vimentin was detected in taste bud cells, and synaptophysin reacted to the taste buds and nerve bundles. The current study of the Greek tortoise oropharyngeal floor investigated its herbivorous eating habits using its serrated lower rhamphotheca, a large tongue with differently shaped papillae, and numerous mucous glands. RESEARCH HIGHLIGHTS: The Greek tortoise (T. graeca graeca) oropharyngeal floor showed many anatomical structures: lower rhamphotheca, paralingual ridge, lower alveolar ridge, tongue, laryngeal mound, and glottis. SEM and light microscopy observations of the tongue revealed varied types and shapes of lingual papillae with a porous surface on the tongue apex (rectangular or conical filiform papillae), on the tongue body (filiform and fungiform papillae), and on the tongue root (dagger-shaped, conical, bifurcated, and leaf-like papillae). Light microscopy findings: the lamina propria constituted the core of the lingual papillae and had numerous mucous glands that had a slightly magenta-red color with PAS reagent. The apical surface of the fungiform papillae had taste pores. Vimentin and synaptophysin gave a reaction to the taste buds.

A novel immunofluorescence study of Lingual Salivary Glands in the Egyptian Tortoise (Testudo kleinmanni) and its ecological significance

The Egyptian tortoise (Testudo kleinmanni) is remarkably adapted to its harsh desert environment, a characteristic that is crucial for its survival under extreme conditions. This study was aimed at providing a deeper understanding of the lingual salivary gland structures in the Egyptian tortoise and examining how these structures help the tortoise manage hydration and nutrition in arid conditions. Utilizing a combination of light microscopy and immunofluorescence, this research introduced pioneering methods involving seven different antibodies, marking a first in the study of reptilian salivary glands. Our investigations categorized the tortoise's salivary glands into papillary and non-papillary types. The papillary glands were further classified into superficial, deep, interpapillary, and intraepithelial salivary glands, while non-papillary glands included superficial and deep lingual types. Structurally, these glands are organized into lobules, delineated by interlobular septa, and are equipped with a duct system comprising interlobular, intercalated, and main excretory ducts with gland openings on the tongue's surface and the papillae surfaces. Notably, the superficial glands displayed both tubuloalveolar and acinar configurations, whereas the deep lingual glands were exclusively acinar. Immunofluorescence results indicated that α-smooth muscle actin (α-SMA) was prevalent in myoepithelial cells, myofibroblasts, and blood vessels, suggesting their integral role in glandular function and support. E-cadherin was predominantly found in epithelial cells, enhancing cell adhesion and integrity, which are critical for efficient saliva secretion. Importantly, Mucin 1 (MUC1) and Mucin 5B (MUC5B) staining revealed that most glands were mucous in nature, with MUC5B specifically marking mucin within secretory cells, confirming their primary function in mucous secretion. PDGFRα and CD34 highlighted the presence of telocytes and stromal cells within the glandular and interlobular septa, indicating a role in structural organization and possibly in regenerative processes. Cytokeratin 14 expression was noted in the basal cells of the glands, underscoring its role in upholding the structural foundation of the epithelial barrier. In conclusion, this detailed morphological and immunological characterization of the Egyptian tortoise's salivary glands provides new insights into their complex structure and essential functions. These findings not only enhance our understanding of reptilian physiology but also underline the critical nature of salivary glands in supporting life in arid environments. This study's innovative use of a broad range of immunofluorescence markers opens new avenues for further research into the adaptive mechanisms of reptiles.

Macro- and micro-anatomical investigation of the oropharyngeal roof of landform greek tortoise (Testudo graeca graeca) and semi-aquatic red-eared slider turtle (Trachemys scripta elegans)

The present investigation examined the oropharyngeal roof of two turtles having different feeding behaviors: the landform Greek tortoise (Testudo graeca graeca) primarily herbivores and the semi-aquatic red-eared slider turtle (Trachemys scripta elegans) lives in freshwater that opportunistic omnivorous grossly and by scanning and light microscopes. Grossly, the Greek tortoise had a V-shaped roof consisting of the upper rhamphotheca, peri-palatine region, upper alveolar ridge, peripheral palatine ridge, median palatine ridge, vomer, choanae, caudal palatine part, and pharynx. At the same time, the red-eared slider had a semilunar roof consisting of upper rhamphotheca, two peripheral palatine ridges, core of palatine ridges, upper alveolar band, vomer, choanae, caudal palatine part, and pharynx. SEM revealed that the red-eared slider roof appeared more straightforward. The upper rhamphotheca is sharp, with a median premaxillary notch in the red-eared slider that gives a powerful bite for cutting to compensate absence of the teeth. Additionally, the red-eared slider's upper alveolar band is interrupted by a single upper alveolar ridge that appears spiky, pointed, and longer as it needs powerful chewing of prey and there are two types of teeth-like projections at its peri-palatine area for food-crushing and chewing. The Greek tortoise palatine region had numerous ridges and folds to provide roughness for food processing. Greek tortoises had small-sized choanae with two choanal folds to minimize choanal openings when eating dusty grasses. Histologically, Greek tortoise palate was rostrally thicker and more keratinized than caudally, and the caudal palatine region was characterized by a single pair of circumvallate-like papilla with multiple mucous openings and secretions, while red-eared slider palate was slightly keratinized at the peri-choanal region, and the rest of the palate was non-keratinized with few mucous openings. The current investigation found various structural oropharyngeal roof adaptations to feeding behavior in the omnivore red-eared slide compared to the herbivorous Greek turtle.

The tongue of the red-eared slider (Trachemys scripta elegans): morphological characterization through gross, light, scanning electron, and immunofluorescence microscopic examination

The red-eared slider (Trachemys scripta elegans) is renowned for its remarkable adaptations, yet much of its complex biology remains unknown. In this pioneering study, we utilized a combination of gross anatomy, scanning electron microscopy (SEM), light microscopy, and immunofluorescence techniques to examine the tongue's omnivorous adaptation in this species. This research bridges a critical knowledge gap, enhancing our understanding of this intriguing reptile. Gross examination revealed a unique arrowhead-shaped tongue with a median lingual fissure and puzzle-piece-shaped tongue papillae. SEM unveiled rectangular filiform, conical, and fungiform papillae, with taste pores predominantly on the dorsal surface and mucous cells on the lateral surface of the papillae. Histologically, the tongue's apex featured short rectangular filiform and fungiform papillae, while the body exhibited varying filiform shapes and multiple taste buds on fungiform papillae. The tongue's root contained lymphatic tissue with numerous lymphocytes surrounding the central crypt, alongside lingual skeletal musculature, blood and lymph vessels, and Raffin corpuscles in the submucosa. The lingual striated muscle bundles had different orientations, and the lingual hyaline cartilage displayed a bluish coloration of the ground substance, along with a characteristic isogenous group of chondrocytes. Our research represents the first comprehensive application of immunofluorescence techniques to investigate the cellular intricacies of the red-eared slider's tongue by employing seven distinct antibodies, revealing a wide array of compelling and significant findings. Vimentin revealed the presence of taste bud cells, while synaptophysin provided insights into taste bud and nerve bundle characteristics. CD34 and PDGFRα illuminated lingual stromal cells, and SOX9 and PDGFRα shed light on chondrocytes within the tongue's cartilage. CD20 mapped B-cell lymphocyte distribution in the lingual tonsil, while alpha smooth actin (α-SMA) exposed the intricate myofibroblast and smooth muscle network surrounding the lingual blood vessels and salivary glands. In conclusion, our comprehensive study advances our knowledge of the red-eared slider's tongue anatomy and physiology, addressing a significant research gap. These findings not only contribute to the field of turtle biology but also deepen our appreciation for the species' remarkable adaptations in their specific ecological niches.

Scanning electron microscopic and histological features of the oral cavity of the Egyptian tortoise (Testudo kleinmanni)

This investigation was led to depict the structural and functional adaptations of the oral cavity of herbivorous Egyptian tortoises using scanning electron and light microscopes. The SEM showed that the triangular papillary tongue possessed three conical papillary subtypes: the rectangular conical on the tip, the round conical on the rest of the dorsal lingual surface and the elongated conical on the caudal portion of the lingual wing. The presence of the serrated lips with their valves compensated for the absence of the teeth. The rostral part had a vomeronasal opening while the middle part had the choana, but the caudal part had numerous openings of the salivary glands. There are three palatine folds: a single median palatine fold, two peripheral palatine folds and the choanal fold. The current histological results show the keratinized dorsal lingual surface, in which the keratinized layer extended to cover the papillae. Two types of lingual glands, according to their position, are papillary superficial and deep lingual glands. Papillary or superficial glands open in the interpapillary spaces via narrow openings, while the deep glands are surrounded by well-developed muscles and open via wide openings on the dorsal lingual surface. An entoglossal cartilaginous structure of hyaline cartilage was found in the mid- and hindtongue, with numerous chondrocytes lodged within the lacunae. Our results conclude that the oral cavity of the herbivorous Egyptian tortoise was adapted to the dietary and vigorous demands of the Egyptian fauna.

Oropharyngeal cavity floor morphology in Eretmochelys imbricata (Testudines: Cheloniidae) hatchlings and evolutionary implications

Morphological studies of the oropharyngeal cavity of chelonians have become an interesting tool in the understanding of evolutionary processes associated with feeding habits in aquatic animals and the transition from aquatic to terrestrial forms. In this context, the aim of the present study was to describe the oropharyngeal cavity floor morphology of hawksbill sea turtle (Eretmochelys imbricata) hatchlings. Ten dead hatchlings of undefined sex were obtained from nests hatched on the coast of the state of Rio Grande do Norte, Brazil. The heads of each specimen were fixed, dissected, and analyzed at the macroscopic and microscopic levels. The oropharyngeal cavity floor of the hawksbill sea turtle hatchlings is formed by the tongue, pharynx, floor muscles, and hyolingual skeleton, delimited in the rostral and lateral directions by a keratinized beak, called the rhamphotheca, and in the caudal region at the limit between the pharynx and the esophagus. The tongue muscles and the muscles that support the floor of the oral cavity comprise the following: m. hypoglossohyoideus, m. hypoglossoglossus, m. hyoglossus, m. genioglossus, m. constrictor laryngis, m. geniohyoideus pars lateralis, and m. intermandibularis. The oropharyngeal cavity floor mucosa is formed by keratinized stratified squamous epithelium and the lamina propria is formed by loose connective tissue. The floor mucosa is devoid of taste buds. We believe that the basic oropharyngeal cavity floor characteristics in hawksbill sea turtle hatchlings may comprise indications that these animals are plesiomorphic and that semiaquatic and terrestrial turtles may have undergone adaptations to feed out of water.

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.

Musculoskeletal architecture of the prey capture apparatus in salamandrid newts with multiphasic lifestyle: does anatomy change during the seasonal habitat switches?

Some newt species change seasonally between an aquatic and a terrestrial life as adults, and are therefore repeatedly faced with different physical circumstances that affect a wide range of functions of the organism. For example, it has been observed that seasonally habitat-changing newts display notable changes in skin texture and tail fin anatomy, allowing one to distinguish an aquatic and a terrestrial morphotype. One of the main functional challenges is the switch between efficient aquatic and terrestrial prey capture modes. Recent studies have shown that newts adapt quickly by showing a high degree of behavioral flexibility, using suction feeding in their aquatic stage and tongue prehension in their terrestrial stage. As suction feeding and tongue prehension place different functional demands on the prey capture apparatus, this behavioral flexibility may clearly benefit from an associated morphological plasticity. In this study, we provide a detailed morphological analysis of the musculoskeletal system of the prey capture apparatus in the two multiphasic newt species Ichthyosaura alpestris and Lissotriton vulgaris by using histological sections and micro-computed tomography. We then test for quantitative changes of the hyobranchial musculoskeletal system between aquatic and terrestrial morphotypes, The descriptive morphology of the cranio-cervical musculoskeletal system provides new insights on form and function of the prey capture apparatus in newts, and the quantitative approach shows hypertrophy of the hyolingual musculoskeletal system in the terrestrial morphotype of L. vulgaris but hypertrophy in the aquatic morphotype of I. alpestris. It was therefore concluded that the seasonal habitat shifts are accompanied by a species-dependent muscular plasticity of which the potential effect on multiphasic feeding performance in newts remains unclear.

Feeding behaviour in a 'basal' tortoise provides insights on the transitional feeding mode at the dawn of modern land turtle evolution

Almost all extant testudinids are highly associated with terrestrial habitats and the few tortoises with high affinity to aquatic environments are found within the genus Manouria. Manouria belongs to a clade which forms a sister taxon to all remaining tortoises and is suitable as a model for studying evolutionary transitions within modern turtles. We analysed the feeding behaviour of Manouria emys and due to its phylogenetic position, we hypothesise that the species might have retained some ancestral features associated with an aquatic lifestyle. We tested whether M. emys is able to feed both in aquatic and terrestrial environments. In fact, M. emys repetitively tried to reach submerged food items in water, but always failed to grasp them—no suction feeding mechanism was applied. When feeding on land, M. emys showed another peculiar behaviour; it grasped food items by its jaws—a behaviour typical for aquatic or semiaquatic turtles—and not by the tongue as generally accepted as the typical feeding mode in all tortoises studied so far. In M. emys, the hyolingual complex remained retracted during all food uptake sequences, but the food transport was entirely lingual based. The kinematical profiles significantly differed from those described for other tortoises and from those proposed from the general models on the function of the feeding systems in lower tetrapods. We conclude that the feeding behaviour of M. emys might reflect a remnant of the primordial condition expected in the aquatic ancestor of the tortoises.

The oropharyngeal morphology in the semiaquatic giant Asian pond turtle, Heosemys grandis, and its evolutionary implications

The oropharynx as a functional entity plays a fundamental role in feeding. Transitions from aquatic to terrestrial lifestyles in vertebrates demanded major changes of the oropharynx for the required adaptations to a different feeding environment. Extant turtles evolved terrestrial feeding modes in three families (testudinids, emydids, geoemydids)-independently from other amniotes-and are therefore important model organisms to reconstruct morpho-functional changes behind aquatic-terrestrial transitions. In this study we hypothesized that the oropharyngeal morphology in semiaquatic turtles of the geoemydid family shows parallels to testudinids, the only purely terrestrial extant lineage. We provide an in-depth description of the oropharynx in the semiaquatic geoemydid Heosemys grandis by using a combination of micro computed tomography (micro-CT) and subsequent digital in situ 3-D reconstruction, scanning electron microscopy (SEM), and histology. We show that H. grandis has a large tongue with rough papillose surface and well-developed lingual muscles. The attachment sites of the lingual muscles on the hyolingual skeleton and their courses within the tongue are nearly identical with testudinids. The hyolingual skeleton itself is mainly cartilaginous and shows distinct-but compared to testudinids rather small-anterior extensions of the hyoid body and hypoglossum. Oral glands are well developed in H. grandis but are smaller and simpler than in testudinids. Similarly, oropharyngeal keratinization was minimal and found only in the anterior palate, regions close to the beak, and tongue tip. We conclude that H. grandis shows distinct oropharyngeal morpho-functional adaptations for a terrestrial lifestyle but still retains characters typical for aquatic forms. This makes this species an important example showing the oropharyngeal adaptations behind aquatic-terrestrial transitions in turtles.

Myoanatomy and serotonergic nervous system of plumatellid and fredericellid Phylactolaemata (Lophotrochozoa, Ectoprocta)

The phylogenetic position of the Ectoprocta within the Lophotrochozoa is discussed controversially. For gaining more insight into ectoproct relationships and comparing it with other potentially related phyla, we analysed the myoanatomy and serotonergic nervous system of adult representatives of the Phylactolaemata (Plumatella emarginata, Plumatellavaihiriae, Plumatella fungosa, Fredericella sultana). The bodywall contains a mesh of circular and longitudinal muscles. On its distal end, the orifice possesses a prominent sphincter and continues into the vestibular wall, which has longitudinal and circular musculature. The tentacle sheath carries mostly longitudinal muscle fibres in Plumatella sp., whereas F. sultana also possesses regular circular muscle fibres. Three groups of muscles are associated with the lophophore: 1) Lophophoral arm muscles (missing in Fredericella), 2) epistome musculature and 3) tentacle musculature. The epistome flap is encompassed by smooth muscle fibres. A few fibres extend medially over the ganglion to its proximal floor. Abfrontal tentacle muscles have diagonally arranged muscle fibres in their proximal region, whereas the distal region is formed by a stack of muscles that resemble an inverted 'V'. Frontal tentacle muscles show more variation and either possess one or two bases. The digestive tract possesses circular musculature which is striated except at the intestine where it is composed of smooth muscle fibres. The serotonergic nervous system is concentrated in the cerebral ganglion. From the latter a serotonergic nerve extends to each tentacle base. In Plumatella the inner row of tentacles at the lophophoral concavity lacks serotonergic nerves. Bodywall musculature is a common feature in many lophotrochozoan phyla, but among other filter feeders like the Ectoprocta is only present in the 'lophophorate' Phoronida. The longitudinal tentacle musculature is reminiscent of the condition found in phoronids and brachiopods, but differs to entoproct tentacles. Although this study shows some support for the 'Lophophorata', more comparative analyses of possibly related phyla are required.