Anatomical Record-Advances in Integrative Anatomy and Evolutionary Biology最新文献

Chameleons are a family of lizards distinguished by several unique features related to their arboreal lifestyles, such as a ballistic tongue, skin color changes, independent movement of both eyes, a prehensile tail, and cleft hands and feet. The veiled chameleon (Chamaeleo calyptratus) has been proposed as a promising model species for studying squamate biology. Despite its potential, the developmental biology of this species remains poorly understood, particularly in terms of gonadal development. This study aimed to elucidate the development of the gonads in the veiled chameleon, from the initial appearance of the gonadal ridges through the sexual differentiation into ovaries and testes, to the establishment of the gonadal structures in both sexes. The study showed the accelerated appearance of gonadal primordia compared to the soma in the veiled chameleon, which is unique and possibly influenced by a prolonged in ovo development period due to the slowed rate of embryonic development in this species. The undifferentiated gonads are characterized by a voluminous medulla and a thin cortex. The process of gonadal sexual differentiation mirrors that seen in other vertebrates. Ovarian differentiation involves the development of a cortex containing germ cells and the loss of these cells in the medulla. Differentiated ovaries are characterized by a thin cortex and early induction of meiosis, leading to the formation of ovarian follicles before hatching. In contrast, testis differentiation involves the loss of germ cells from the cortex, its transformation into a thin epithelium, and the development of germ cell-containing testis cords in the medulla. The testis cords originate from invagination and remain without forming a lumen during embryogenesis. This comprehensive examination of gonadal development in the veiled chameleon provides important insights into sexual differentiation processes in this species. Moreover, it may stimulate further, broader studies in vertebrate developmental biology.

Xenodens calminechari is a mosasaurid taxon named by Longrich et al. (2021) based on the holotype MHNM.KH.331, a left maxilla with several teeth. This holotype was obtained nonscientifically (without technical supervision) from an area in Morocco that yields many manipulated or forged specimens. Examination of Longrich et al. (2021) reveals four tooth crowns occupy what appear to be two alveoli in MHNM.KH.331, and there is potential adhesive connecting the tooth crowns to the maxilla on their lateral sides. We argue that the articulated tooth crowns of this taxon were artificially placed in the maxilla, rendering at least two apomorphies of this taxon the product of forgery. Longrich et al. (2021)'s claims of fused tooth 'roots' in MNHM.KH.331 are instead calcified periodontal ligament and alveolar bone that have ankylosed, resembling the typical mosasaurid condition. Differing tooth crown morphology does not preclude the referral of the teeth of this specimen to a younger ontogenetic stage of another mosasaur (possibly Carinodens) because many extant lizard species show drastic ontogenetic changes in the dentition. We argue that Xenodens calminechari represents a nomen dubium. This specimen constitutes a confluence of two persistent problems in vertebrate paleontology: material sourced from commercial excavations that has not been adequately tested for forgery, and taxa named from tooth-based holotypes that ignore the potential for intraspecific dental variation and interspecific convergence in dental characters, as are common in squamates. We suggest that Longrich et al. CT scan MHNM.KH.331, and we supply CT examples for identifying artificially added tooth crowns to Moroccan mosasaur jaws. Finally, we provide recommendations for the designation of mosasaurid holotypes.

Spatial relationships between oropharyngeal structures and their coordinated dynamics ensure proper adaptations in functions such as respiration, chewing, and swallowing. Thus, the aim of this study is to analyze spatial changes in the normal oropharynx during respiration and mastication. For this purpose, eight 7-8 months old Yucatan minipigs, four of each sex were used. X-ray fluoroscopy was recorded with the field of view focused on the oropharyngeal region. The x-ray video clips showing respiratory cycles and masticatory sequences were digitized and traced. Points to be digitized and traced were located on the soft palate, epiglottis, tongue base, and pharyngeal wall. An X-Y coordinate system was established to trace distances and directions of each structure (structural), and between structures (inter-structural) during phases of respiration, chewing stages, and swallowing episodes. During respiration, the soft palate showed the largest X-Y movements with the largest distance change (1.32 ± 0.64 mm). In contrast, distance changes in the tongue base were significantly smaller (0.32 ± 0.21 mm, p < 0.05). Notably, during chewing the tongue base and epiglottis showed major changes in distance and direction. Similarly, during swallowing the tongue base showed the largest changes (2.94 ± 1.28 mm) followed by the pharyngeal wall and epiglottis. Thus, although coordinated, each pharyngeal structure plays specific roles. Understanding of these spatial and specific dynamics in different oropharyngeal structures would provide the baseline to analyze the potential mechanisms of various swallowing and breathing disorders such as dysphagia and obstructive sleep apnea.

Although toothed whales have dentition peculiar to mammals, little attention has been paid to the periodontal tissues that support these characteristic teeth. In this study, we clarified the anatomical characteristics of the periodontal tissue in several species of Delphinidae through three-dimensional observation using micro-computed tomography, histological observations using decalcified sections, and immunohistochemical analysis. The results indicated that the teeth and the periodontal tissues of dolphins are morphologically unique among mammals. The alveolar bone was both crude and spongy. The lamina dura, a radiopaque line observed in the alveolar bone of common mammals, was thin in dolphins, and the teeth were attached to the trabeculae with the periodontal ligament (PDL). The alveolar sockets were massive for the size of the teeth. The PDL, a collagen fiber that fills the periodontal space, was well-developed and peculiarly divided into two layers. The inner layer fibers radially spread out from the cementum, similar to the PDL in common mammals. However, the outer layer fibers penetrate the spongy bone in a complicated manner. The interstitial space between the inner and outer layers contained nerve fiber bundles that were thicker than those found in the PDL of other mammals. Sensory receptor-like structures were observed at the terminal ends of the nerve fibers. These findings indicated that the dolphin PDL is more sensitive to dental stimuli than those of other mammals, suggesting that the dolphin dentition plays a functional role as a sensory receptor, similar to tactile hair.

Insects process their food with their cuticle-based mouthparts. These feeding structures reflect their diversity and can, in some cases, showcase adaptations in material composition, mechanical properties, and shape to suit their specific dietary preferences. To pave the way to deeply understand the interaction between mouthparts and food and to determine potential adaptations of the structures to the food, this study focuses on the mandibles of two praying mantis species. Gongylus gongylodes feeds mainly on Diptera, and Sphodromantis lineola forages on larger prey. Employing scanning electron microscopy, the mandibular morphologies were analyzed. The degree of the cuticle tanning was tested using confocal laser scanning microscopy. Furthermore, the contents of transition and alkaline earth metals in the mandible cuticle were studied using energy-dispersive X-ray spectroscopy and the mechanical properties tested by nanoindentation. We found that S. lineola mandibles show pronounced gradients of Young's modulus and hardness from the basis to the tip, which might be an adaptation against high stresses during biting and chewing. G. gongylodes, in contrast, did not show pronounced gradients, which may indicate that there is less stress involved in feeding-necessary to test in future studies. The mechanical properties of manidibles in both species are related to the degree of cuticle tanning but also positively correlate with the content of magnesium. These findings enrich our understanding of insect cuticle biology but also present new sets of data on praying mantis structures.

Osteohistological evidence is widely used to infer paleobiological traits of fossil vertebrates, such as ontogeny and growth rates. Mesosaurs, an enigmatic group of aquatic reptiles from the early Permian, are the most well-known Paleozoic amniotes from Africa and South America. Their fossils are abundant in South America, ranging from the central-west region of Brazil to the southernmost areas, as well as parts of Paraguay and Uruguay. In this contribution, we examined the bone microstructure of Mesosaurus tenuidens by analyzing thin sections of axial and appendicular elements of several specimens collected from various Brazilian sites. The microstructure of the bones showed minimal histological variability among elements, predominantly composed of parallel-fibered tissues, indicating slow growth rhythm, along with increased bone density attributed to pachyosteosclerosis. The cortical area consists of poorly vascularized parallel-fibered bone tissue, which was interrupted by multiple cyclical growth marks, some of them being supernumerary, suggesting a strong influence of seasonality. Moreover, the organization of growth marks suggests distinct life history trajectories among individuals collected from different outcrops, reflecting environmental heterogeneity throughout the basin. Internally, the endosteal domain exhibits greater vascularization compared to the cortices and frequently contained calcified cartilage. In the ontogenetic series, there was a progressive filling of the medullary region from small to large individuals. The presence of the External Fundamental System (a proxy indicating somatic maturity) was observed in femora and ribs, suggesting that determinate growth was already occurring in Permian mesosaurs and may not be an exclusive specialization of crown amniotes.

The effects and consequences of changes in thyroid hormones (THs) level are among the actively studied topics in teleost developmental and evolutionary biology. In most of the experimental models used, the altered hormonal status (either hypo- or hyperthyroidism) is a stable characteristic of the developing organism, and the observed phenotypic outcomes are the cumulative consequences of multiple TH-induced developmental changes. Meanwhile, the influence of the transient fluctuations of TH content on skeleton development has been much less studied. Here, we present experimental data on the developmental effects and phenotypic consequences of transient, pharmacologically induced thyrotoxicosis and hypothyroidism at different stages of ossified skeleton patterning in zebrafish. According to the results, the skeleton structures differed in TH sensitivity. Some showed a notable shift in the developmental timing and rate, while other demonstrated little or no response to changes in TH content. The developmental stages also differed in TH sensitivity. We identified a relatively short developmental period, during which changes in TH level significantly increased the developmental instability and plasticity, leading to phenotypic consequences comparable to those in fish with a persistent hypo- or hyperthyroidism. These findings allow this period to be considered as a critical developmental window.

In women and animal models, hypothyroidism induces hypercholesterolemia, pancreatitis, and insulitis. We investigated whether lipids are involved in the effects of hypothyroidism in the pancreas. Control (n = 6) and hypothyroid (n = 6) adult female rabbits were used. We quantified serum and pancreatic triacylglycerol and total cholesterol levels, the oxidative and antioxidant status, and the expression of low-density lipoprotein cholesterol receptor (LDLR) in the pancreas. Inflammation of the pancreas was evaluated by infiltration of immune cells positive to CD163 and α-farnesoid receptor (FXRα). Other lipid players involved in both inflammation and insulin secretion of the pancreas, such as lanosterol 14-α-demethylase (CYP51A1), β-farnesoid receptor (FXRβ), 3β-hydroxysteroid dehydrogenase (3β-HSD), and peroxisome proliferator-activated receptor β (PPARβ/δ), were quantified. Groups were compared by t-Student or U-Mann-Whitney tests (p ≤ 0.05). Hypothyroidism induced hypercholesterolemia and a high cholesterol accumulation in the pancreas of female rabbits, without affecting oxidative or antioxidative status nor the expression of LDLR. The pancreas of hypothyroid females showed inflammation identified by a great infiltration of immune cells, macrophages CD163+, and loss of expression of FXRα+ in immune cells. Moreover, a reduced expression of CYP51A1, FXRβ, and PPARβ/δ, but not 3β-HSD, in the hypothyroid pancreas was found. Pancreatitis and insulitis promoted by hypothyroidism may be related to the accumulation of cholesterol, lanosterol actions, and the activation of PPARβ/δ. All inflammatory markers evaluated in this study are related to glucose regulation, suggesting the link between hypothyroidism and diabetes.

The functional morphology and kinematics of the elbow joint remain relatively understudied in squamates. Previous investigations of lizard elbow morphology and kinematics suggest long-axis rotation (LAR) of the radius and ulna during stance allows the manus to remain pronated during forelimb retraction. Using XROMM (X-ray Reconstruction of Moving Morphology), we explored the range of 3D movements and kinematics of the humerus, radius, and ulna in three adult male Central bearded dragons (Pogona vitticeps) during trackway walking. Our data indicate that the elbow joint of P. vitticeps experiences significant rotations in all three dimensions and that the radius and ulna adduct and rotate laterally on their long axes relative to the elbow joint and to one another during stance. These movements allow the distal ends of the radius and ulna to remain in a configuration necessary for manus pronation. These data support previous inferences that the radius and ulna of lizards move independently at the wrist joint. We suggest that independent LAR of the radius and ulna relative to the elbow joint and to one another may be an ancestral mechanism in lizards and perhaps more broadly across non-avian reptiles.

While being the largest living terrestrial mammals, elephants are best known for their highly modified and uniquely elaborate craniofacial anatomy-most notably with respect to their often-massive tusks and intricately muscular, multifunctional proboscis (i.e., trunk). For over a century, studies of extinct proboscidean relatives of today's elephants have presented hypotheses regarding the evolutionary history of the crania and tusks of these animals and their bearing on the evolution of the proboscis. Herein, I explore major functional characteristics of the proboscidean head. I give a brief review of the anatomy of tusks and dentition, the feeding apparatus, and proboscis in extant elephants and explore their overall bearing in elephant feeding behavior as well as other aspects of their ecology. I also review the evolution of the proboscidean head, with a synthetic analysis of studies and further speculation exploring the interconnected evolutionary roles of tusk morphology and use, feeding anatomy and functional implications thereof, and proboscis anatomy and use in the ancestry of elephants. Notable emphasis is given to the evolutionary role of initial elongation of the mandibular symphysis in the development of the proboscis in many proboscideans. Subsequent secondary shortening of the symphysis and elevation of the temporal region and occiput allowed for a pendulous trunk and proal feeding in living elephants and other proboscidean groups with highly lophodont dentition.