Showing papers in "Journal of Morphology in 2023"
TL;DR: In this paper , the authors extend the Carnegie staging system to two additional cetacean taxa: the beluga whale (Delphinapterus leucas, Odontoceti), and the bowhead whale (Balaena mysticetus, Mysticeti).
Abstract: Embryogenesis of cetaceans (whales, dolphins, porpoises) is best known in Stenella attenuata, the pan‐tropical spotted dolphin, based on a remarkably complete and well‐studied prenatal ontogenetic series. Our study expands understanding of cetacean embryology by adding two additional cetacean taxa: the beluga whale (Delphinapterus leucas, Odontoceti), and the bowhead whale (Balaena mysticetus, Mysticeti). We identify key features that characterize these taxa at specific stages and highlight heterochrony between the odontocetes and mysticetes. The toothed whales are more similar in developmental timing to each other than either is to Balaena. The two odontocete taxa, Stenella and Delphinapterus, share similar developmental trajectories while early Balaena specimens differ from the odontocetes. This developmental variation proves challenging to ascribe to the existing Carnegie staging system. Most notably, flippers, hindlimbs, and flukes all provide morphological traits for characterization within the Carnegie staging system. A presomitic Delphinapterus embryo is also described. This study applies the Carnegie staging system to two more cetacean taxa and forms a framework for future research on cetacean developmental genetics and the modeling of fetal growth.
2 citations
TL;DR: In this article , the authors used multibody dynamics analysis and finite element analysis to simulate a rat skull and compared models with and without cranial sutures, and found that the presence of cranial Sutures in the rat model does not substantially change overall strain gradients across the cranium.
Abstract: Cranial sutures are fibrocellular joints between the skull bones that are progressively replaced with bone throughout ontogeny, facilitating growth and cranial shape change. This transition from soft tissue to bone is reflected in the biomechanical properties of the craniofacial complex. However, the mechanical significance of cranial sutures has only been explored at a few localised areas within the mammalian skull, and as such our understanding of suture function in overall skull biomechanics is still limited. Here, we sought to determine how the overall strain environment is affected by the complex network of cranial sutures in the mammal skull. We combined two computational biomechanical methods, multibody dynamics analysis and finite element analysis, to simulate biting in a rat skull and compared models with and without cranial sutures. Our results show that including complex sutures in the rat model does not substantially change overall strain gradients across the cranium, particularly strain magnitudes in the bones overlying the brain. However, local variations in strain magnitudes and patterns can be observed in areas close to the sutures. These results show that, during feeding, sutures may be more important in some regions than others. Sutures should therefore be included in models that require accurate local strain magnitudes and patterns of cranial strain, particularly if models are developed for analysis of specific regions, such as the temporomandibular joint or zygomatic arch. Our results suggest that, for mammalian skulls, cranial sutures might be more important for allowing brain expansion during growth than redistributing biting loads across the cranium in adults.
2 citations
TL;DR: In this paper , a variety of morphological solutions to this constraint, including a reduction of the anterior dentition, special arrangements of canines and incisors, and the nesting of the mandibular cheek teeth within the maxillary ones, were proposed.
Abstract: The evolution of mammals is characterized, amongst other developments, by an increasing relevance of effective food processing in form of an increasingly durable dentition, complex occlusal surfaces, and transverse chewing movements. Some factors have received increasing attention for the facilitation of the latter, such as the configuration of the jaw joint, the chewing muscle arrangement and lever arms, or the reduction of interlocking cusps on the cheek teeth occlusal surface. By contrast, the constraining effect of the anterior dentition (incisors and canines) on transverse chewing motions, though known, has received less comprehensive attention. Here, we give examples of this constraint in extant mammals and outline a variety of morphological solutions to this constraint, including a reduction of the anterior dentition, special arrangements of canines and incisors, the nesting of the mandibular cheek teeth within the maxillary ones, and the use of different jaw positions for different dental functions (cropping vs. grinding). We suggest that hypselodont anterior canines or incisors in some taxa might represent a compensatory mechanism for self‐induced wear during a grinding chewing motion. We propose that the diversity in anterior dentition among mammalian herbivores, and the evolutionary trend towards a reduction of the anterior dentition in many taxa, indicates that the constraining effect of the anterior dentition, which is rigidly linked to the cheek teeth by the osseous jaws, represents a relevant selective pressure in mammalian evolution.
2 citations
TL;DR: In this paper , the internal ultrastructure of the scolex and the histochemical composition of the apical glands of two South American proteocephalideans cestodes, Monticellia magna and Proteocephalus pimelodi, were described for the first time.
Abstract: The internal ultrastructure of the scolex and the histochemical composition of the apical glands of two South American proteocephalideans cestodes, Monticellia magna and Proteocephalus pimelodi, were described for the first time. The study included the use of scanning and transmission electron microscopy to observe the tegumental ultrastructure, and histochemical techniques to detect types of gland secretion. Two types of glands were found in the scolex of M. magna and P. pimelodi. The pattern of microtriches described for M. magna was confirmed and that of P. pimelodi was described for the first time. Also, the internal ultrastructure of the microtriches in both species was described. Indications of the presence of sensory receptors were also found in M. magna. Finally, the systematic value of the characters studied is discussed, such as the internal structure of the gladiate spinitriches and the apocrine gland of M. magna.
1 citations
TL;DR: In this article , the expression of different glycosidic residues (Gr) in the near-term placenta constitutes its glycotype, and a matrix was constructed to map and infer phylogenetic and evolutionary relationships.
Abstract: The main evolutionary milestone in the oviparity–viviparity transition is placentation. The placenta is an organ with great morphological diversity among eutherians. The expression of different glycosidic residues (Gr) in the near‐term placenta constitutes its glycotype. In this study, the expression of different Gr was determined by lectin histochemistry in early, midterm, and near‐term placentas of the plains viscacha (Lagostomus maximus), a caviomorph rodent with the highest poliovulatory rate and embryonic resorption rate among eutherians. Besides, a matrix with the expression of each Gr in the exchange trophoblast of viscacha and other eutherians was constructed to map and infer phylogenetic and evolutionary relationships. Between early, midterm, and near‐term placentas, variations in the pattern expression of Gr were observed. The glycotype of the near‐term placenta is composed of a high diversity of Gr. Reconstruction of the ancestral state for each Gr present in the near‐term placenta showed a diverse scenario: some sugars were common to the species of Placentalia included in this study. In the analyzed species with synepitheliochorial and epitheliochorial placentas, no differential glycosylation patterns between them were observed. In species with invasive placentas, such as the endotheliochorial placentas of Carnivora, some common Gr were detected among them, while others were species‐specific. In species with hemochorial placenta, the same Gr are shared. Particularly, in the viscacha greater differences with species of the Hominidae and even Muridae families were observed. Nevertheless, greater similarities with other caviomorph rodents were detected. Placental glycotype of each species constitutes an excellent tool to achieve phylogenetic and evolutionary inferences among eutherians.
1 citations
TL;DR: The concept of cell homology lies in the heart of comparative biological science as mentioned in this paper and has shaped the evolutionary paradigm for a century and formed the axis of comparative anatomy and embryology, which accept the identity of structure as a ground measure of relatedness.
Abstract: The concept of homology lies in the heart of comparative biological science. The distinction between homology as structure and analogy as function has shaped the evolutionary paradigm for a century and formed the axis of comparative anatomy and embryology, which accept the identity of structure as a ground measure of relatedness. The advent of single‐cell genomics overturned the classical view of cell homology by establishing a backbone regulatory identity of cell types, the basic biological units bridging the molecular and phenotypic dimensions, to reveal that the cell is the most flexible unit of living matter and that many approaches of classical biology need to be revised to understand evolution and diversity at the cellular level. The emerging theory of cell types explicitly decouples cell identity from phenotype, essentially allowing for the divergence of evolutionarily related morphotypes beyond recognition, as well as it decouples ontogenetic cell lineage from cell‐type phylogeny, whereby explicating that cell types can share common descent regardless of their structure, function or developmental origin. The article succinctly summarizes current progress and opinion in this field and formulates a more generalistic view of biological cell types as avatars, transient or terminal cell states deployed in a continuum of states by the developmental programme of one and the same omnipotent cell, capable of changing or combining identities with distinct evolutionary histories or inventing ad hoc identities that never existed in evolution or development. It highlights how the new logic grounded in the regulatory nature of cell identity transforms the concepts of cell homology and phenotypic stability, suggesting that cellular evolution is inherently and massively network‐like, with one‐to‐one homologies being rather uncommon and restricted to shallower levels of the animal tree of life.
1 citations
TL;DR: In this article , the ultrastructural anatomy of the cornea, iris and anterior chamber in the eyes of the Shorthead lamprey Mordacia mordax (Mordaciidae, Agnatha) in both downstream and upstream migrant phases of its protracted lifecycle was investigated.
Abstract: The Shorthead lamprey Mordacia mordax (Mordaciidae, Agnatha) represents one of the earliest stages of vertebrate evolution. This study investigates the ultrastructural anatomy of the cornea, iris and anterior chamber in the eyes of this species in both the downstream and upstream migrant phases of its protracted lifecycle to assess the morphological and quantitative changes associated with growth, corneal function and vision. Using light and both scanning and transmission electron microscopy, the cornea is found to be divided into dermal and scleral components separated by a mucoid layer. A range of distinguishing corneal features are compared in the two adult phases of the lifecycle, including epithelial microprojections, mucus‐secreting epithelial cells, the number, thickness, formation and level of branching and anastomosing of collagen lamellae, the type and distribution of vertical sutures, the structure of the mucoid layer and annular ligament and the number and distribution of a large number of basement membranes throughout the cornea. Significant differences are found between the two phases, which are thought to reflect adaptations to the variable environmental conditions encountered throughout this species' lifecycle. The study provides insights into the evolutionary pressures on extant representatives of the earliest stages in the evolution of the vertebrate eye.
1 citations
TL;DR: In this article , the appendicular skeleton of lamniform sharks was used for phylogenetic analysis of the white shark and showed the strength of incorporating new morphological data to resolve the conflict among various previous molecular-based and morphology-based phylogenetic hypotheses.
Abstract: Lamniform sharks are one of the more conspicuous groups of elasmobranchs, including several emblematic taxa as the white shark. Although their monophyly is well supported, the interrelationships of taxa within Lamniformes remains controversial because of the conflict among various previous molecular‐based and morphology‐based phylogenetic hypotheses. In this study, we use 31 characters related to the appendicular skeleton of lamniforms and demonstrate their ability to resolve the systematic interrelationships within this shark order. In particular, the new additional skeletal characters resolve all polytomies that were present in previous morphology‐based phylogenetic analyses of lamniforms. Our study demonstrates the strength of incorporating new morphological data for phylogenetic reconstructions.
1 citations
TL;DR: In this article , the authors investigated geometric evolution of the quadrate in galloanserae, a major clade of extant birds uniting chickenlike (Galliformes) and ducklike (Anseriformes), and performed ancestral shape reconstructions in the context of an up to date neornithine phylogeny.
Abstract: In birds and other reptiles, the quadrate acts as a hinge between the lower jaw and the skull and plays an important role in avian cranial kinesis. Though previous studies have qualitatively described substantial variation in quadrate morphology among birds, none have attempted to quantify evolutionary changes in quadrate shape. Here, we investigate geometric evolution of the quadrate in Galloanserae, a major clade of extant birds uniting chicken‐like (Galliformes) and duck‐like (Anseriformes) fowl. We quantified morphological variation in the quadrate across 50 extant galloanseran species covering all major extant subclades using three‐dimensional geometric morphometrics, and performed ancestral shape reconstructions in the context of an up‐to‐date neornithine phylogeny. We find that our results based only on extant quadrates may overlook plesiomorphic features captured by fossil taxa, resulting in an ancestral state reconstruction for Galloanserae that is seemingly an approximation of the average shape of the extant data set. By contrast, analyses incorporating early fossil galloanseran quadrates (from taxa such as Asteriornis, Presbyornis, and Conflicto) result in ancestral geometric reconstructions more similar to the morphology of extant galliforms, indicating that the quadrate of the last common ancestor of galloanserans may have been more morphologically and functionally similar to those of extant galliforms than to extant anseriforms. These results generally corroborate previous inferences of galloanseran quadrate plesiomorphies and identify several additional plesiomorphic features of the galloanseran quadrate for the first time. Our results illustrate the importance of incorporating fossil taxa into ancestral shape reconstructions and help elucidate important aspects of the morphology and function of the avian feeding apparatus early in crown bird evolutionary history.
1 citations
TL;DR: A survey of osteoderm histology and ornamentation among Crocodylomorpha: a new proxy to infer lifestyle is presented in this article , where the timescale at the top of Figure 6 is shifted to the left, making the stratigraphic occurrences of the taxa in the Figure wrong.
Abstract: Corrigendum to: A survey of osteoderm histology and ornamentation among Crocodylomorpha: a new proxy to infer lifestyle? [Journal of Morphology 2023; 284(1): e21542]. In the original version of the above paper, the timescale at the top of Figure 6 is shifted to the left, making the stratigraphic occurrences of the taxa in the Figure wrong. The new version of Figure 6 provided here corrects this error. The authors apologize for the mistake.
1 citations
TL;DR: In this article , the function of the myzorhynchus and remnant apical organ of adult cestodes in the order Rhinebothriidea was analyzed in 12 species belonging to six genera and two families.
Abstract: The main objective of this study was to analyze the function of the myzorhynchus and remnant apical organ of adult cestodes in the order Rhinebothriidea. Several features of these structures were analyzed in 12 species belonging to six genera and two families. In particular, the glandular composition of the myzorhynchus of four species from Echeneibothriidae (i.e., Notomegarhynchus navonae and three species of Echeneibothrium) was studied using histochemical techniques and/or transmission electron microscopy. In addition, the presence of a remnant apical organ and its glandular composition were analized in six species of Rhinebothriidae and in two species of Semiorbiseptum, whose familial assignment is uncertain. We also evaluated the importance of these characters for diagnosis. The same type of gland cell was found in the myzorhynchus of Echeneibothrium species and in the remnant apical organ of Semiorbiseptum species. These gland cells were Coomassie brilliant blue‐positive, periodic acid Schiff‐positive and Alcian blue‐negative, consistent with a glycoprotein secretion possibly involved in adhesion to the host mucosa and proteolysis. The type of gland cells found in the myzorhynchus of N. navonae were Coomassie brilliant blue‐negative, periodic acid Schiff‐positive and Alcian blue‐positive, consistent with the production of adhesive and protective substances. The type of gland cells in the myzorhynchus and in the remnant apical organ could be a useful character for the generic diagnosis of Echeneibothrium and Semiorbiseptum, respectively. A remnant apical organ was only found in Semiorbiseptum, with its presence/absence being important as a diagnostic character at the generic level for Semiorbiseptum, Scalithrium, and Rhinebothroides. A secondary objective was to characterize the microthrix pattern of the myzorhynchus of N. navonae. An extended distribution of spinitriches was detected, which may allow a better adhesion of this large species to the host mucosa, as the main function of spinitriches is presumably that of adhesion.
TL;DR: In this article , Androgen receptor immunoreactive (AR•IR) nuclei were plotted and the results were quantified with a Heidelberg Topaz II+++scanner and Linocolor 5.0 software.
Abstract: Androgens and their receptors are present throughout the body. Various structures such as muscles, genitals, and prostate express androgen receptors. The central nervous system also expresses androgen receptors. Androgens cross the blood–brain barrier to reach these central areas. In the central nervous system, androgens are involved in multiple functions. The current study investigated in which forebrain areas androgens are expressed in the male cat. Androgen receptor immunoreactive (AR‐IR) nuclei were plotted and the results were quantified with a Heidelberg Topaz II + scanner and Linocolor 5.0 software. The density and intensity of the labeled cells were the main outcomes of interest. The analysis revealed a dense distribution of AR‐IR nuclei in the preoptic area, periventricular complex of the hypothalamus, posterior hypothalamic area, ventromedial hypothalamic, parvocellular hypothalamic, infundibular, and supramammillary nucleus. Numerous AR‐IR cells were also observed in the dorsal division of the anterior olfactory nucleus, lateral septal nucleus, medial and lateral divisions of the bed nucleus of the stria terminalis, lateral olfactory tract nucleus, anterior amygdaloid area, and the central and medial amygdaloid nuclei. AR‐IR nuclei were predominantly observed in areas involved in autonomic and neuroendocrinergic responses which are important for many physiological processes and behaviors.
TL;DR: In this paper , the authors compared the structure of the digestive tracts of scarab beetles Oryctes rhinoceros, Thaumastopeus shangaicus, and Protaetia spp.
Abstract: During pupation, the tissues of holometabolous insects change in preparation for the adult lifestyles, although little literature exists examining this hidden process in detail. Using beetles as a model, we hypothesized that species where the adult and larva have the same diets will show less pronounced changes of the digestive tract during metamorphosis than species where the adults diets differ. We also wanted to observe these changes and document them at a level of detail missing from the current record. We compared the structure of the digestive tracts of scarab beetles Oryctes rhinoceros, Thaumastopeus shangaicus, and Protaetia spp. (Coleoptera: Scarabaeidae)—where the larvae eat wood, soil, or compost while the adults feed on soft plant matter, tree sap, and rotting fruits—with the tortoise beetle, Cassida circumdata (Coleoptera: Chrysomelidae), which feeds on leaves as both larva and adult. In the scarab beetles we observed considerable changes in the digestive tracts during the pupal stage, which we could divide into distinct stages, while in the leaf beetle pupae, the gut did not change. This information can provide new insight into metamorphosis, and the illustrations of what occurs during pupation are novel contributions to this field that will facilitate future work.
TL;DR: In this paper , a detailed description and illustrative three-dimensional anatomical visualization of the musculature of the raptorial forelegs in Mantodea is presented, particularly in the context of functionality and SSD.
Abstract: Prehensile raptorial forelegs are prey capturing and grasping devices, best known for praying mantises (Mantodea) within insects. They show strong morphological and behavioral adaptations toward a lifestyle as generalist arthropod predators. In the past, few species of Mantodea were investigated, concerning morphological variability of the raptorial forelegs. Especially the knowledge of foreleg anatomy in the light of functional and comparative morphology is scarce. Our comparative approach is based on the, for arthropods very common, “female‐biased sexual size dimorphism” (SSD) that occurs in almost every Mantodea species. Within Mantodea, this SSD is likely leading to a shift of the exploited ecological niche between male and female individuals due to changes in, for example, the possible prey size; which might be reflected in the chosen ecomorphs. In this context, we analyzed the musculature of the raptorial forelegs of female and male specimens in five different species with varying SSD, using high‐resolution microcomputed tomography and dissection. We were able to confirm the presence of 15 extrinsic and 15 intrinsic muscles—including one previously undescribed muscle present in all species. Thus, presenting a detailed description and illustrative three‐dimensional anatomical visualization of the musculature in Mantodea. Interestingly, almost no observable differences were found, neither between species, nor between the sexes. Furthermore, we homologized all described muscles, due to their attachment points, to the comprehensive nomenclature established by Friedrich and Beutel (2008), discussed potential functionality of the muscles and possible homologies to the neuropteran Mantispa styriaca (Büsse et al., 2021) and the newly introduced leg nomenclature by Aibekova et al. (2022). By elucidating the anatomy, particularly in the context of functionality and SSD, our results complement previous knowledge of the raptorial forelegs, and facilitate a better understanding of the underlying biomechanical system of the predatory strike, and ultimately, a future comparison to other insect taxa.
TL;DR: In this paper , the authors explored variation in skull morphology among species of the three subfamilies of Viperidae, and test whether that variation correlates with macrohabitat and diet, and found evidence of morphological differentiation between arboreal and terrestrial species and in species with mammal specialist diet.
Abstract: The skull of vipers is a highly kinetic anatomical structure involved in envenomating and consuming of prey. Morphological knowledge about the viperid skull is based on studies on some groups of species, but information on its variation within the whole family and its functional morphology is still scarce. In this study, we aimed to explore variation in skull morphology among species of the three subfamilies of Viperidae, and test whether that variation correlates with macrohabitat and diet. We performed quantitative analyses of the viperid skull based on broad taxonomic sampling and two methodological approaches: linear and geometric morphometrics. The results of both approaches showed that much of the variation lies in differences of shape and relative size of the premaxilla, the nasals, the frontals, and the parietals. The results indicated that phylogeny and size influence the shape of the skull, but we also found evidence of morphological differentiation between arboreal and terrestrial species and in species with mammal specialist diet. Our findings imply that, besides evolutionary allometry and phylogenetic signal, demands of particular diets coupled with use of certain habitats have in part shaped morphological evolution of the viperid skull.
TL;DR: The ultrastructural analysis suggests other functions for the gill besides respiration as discussed by the authors , such as endocytosis and intracellular digestion, and the presence of an intranuclear crystalline structure was frequently associated with chromatin decondensation, swelling of the nuclear envelope and endoplasmic reticulum cisternae and abundance of Golgi stacks.
Abstract: The gill of Aplysia depilans consists of several wedge‐shaped pinnules with a highly folded structure, differing from the typical ctenidial gills of mollusks. Light microscopy and transmission electron microscopy were used to investigate this organ in juveniles and adults. In this species, the gill epithelium comprised ciliated, unciliated, and secretory cells. The ultrastructural analysis suggests other functions for the gill besides respiration. The deep cell membrane invaginations associated with mitochondria in the basal region of epithelium point to a role in ion regulation. Endocytosis and intracellular digestion were other activities detected in epithelial cells. In juveniles, an intranuclear crystalline structure was seen in some ciliated cells. The presence of an intranuclear crystalline structure was frequently associated with chromatin decondensation, swelling of the nuclear envelope and endoplasmic reticulum cisternae, and abundance of Golgi stacks. As these intranuclear inclusions were not found in the gill of the adult specimens, their occurrence in the two juveniles seems likely to be an anomalous condition whose cause cannot be established at the moment. Mucous cells were the most abundant secretory cells in the epithelium, but a few epithelial serous cells were also found. In addition, large protein‐secreting subepithelial cells had the main cell body inserted in the connective tissue and a long thin neck crossing the epithelium. Mucous cells can be considered responsible for the production of the mucus layer that protects the epithelium, but the specific functions of the epithelial and subepithelial protein‐secreting cells remain elusive. Below the epithelium, a layer of connective tissue with muscle cells lined the narrow hemolymph space. The connective tissue included cells with a large amount of rough endoplasmic reticulum cisternae. Bacteria were found on the surface of the gill, and the most abundant had a thin stalk for attachment to the epithelial cells.
TL;DR: In this paper, structural characteristics of the respiratory gas bladder of the osteoglossiform fish Heterotis niloticus have been analyzed and the bladder-vertebrae relationships are also analyzed.
Abstract: This work reports on the structural characteristics of the respiratory gas bladder of the osteoglossiform fish Heterotis niloticus. The bladder‐vertebrae relationships are also analyzed. A slit‐shaped orifice in the mediodorsal pharyngeal wall is surrounded by a muscle sphincter and serves as a glottis‐like opening to the gas bladder. The dorsolateral internal surface of the gas bladder is lined by a parenchyma of highly vascularized trabeculae and septa displaying an alveolar‐like structure. The trabeculae contain, in addition to vessels, numerous eosinophils probably involved in immune responses. The air spaces are endowed with a thin exchange barrier indicating a good potential for respiratory gas exchange. The ventral wall of the gas bladder is a well‐vascularized membrane that exhibits an exchange barrier in the luminal face and an inner structure dominated by the presence of a layer of richly innervated smooth muscle. This is suggestive of an autonomous adjustability of the gas bladder ventral wall. The trunk vertebrae show large transverse processes (parapophyses) and numerous surface openings that lead into intravertebral spaces that become invaded by the bladder parenchyma. Curiously, the caudal vertebrae show a regular teleost morphology with neural and hemal arches, but have similar surface openings and intravertebral pneumatic spaces. The African Arowana hence rivals the freshwater butterfly fish Pantodon in its exceptional role of displaying postcranial skeletal pneumaticity outside of Archosauria. The possible significance of these findings is discussed.
TL;DR: Using geometric morphometrics and comparative phylogenetic methods, the variation in cranial morphology was evaluated for 17 species of heroine cichlids representing five ecomorphs as discussed by the authors .
Abstract: Heroine cichlids are characterized by high morphological diversity, mainly in structures related to the capture and processing of food. The existence of ecomorphological groups has been proposed based on feeding behavior, where it is common for some phylogenetically unrelated species to show evolutionary convergence. Using geometric morphometrics and comparative phylogenetic methods, the variation in cranial morphology was evaluated for 17 species of heroine cichlids representing 5 ecomorphs. Cranial ecomorphs were recovered and significant differences were determined. Morphological variation of the ecomorphs was mainly explained by two axes: (1) the position of the mouth determined by the shape of the bones of the oral jaw and (2) the height of the head, defined by the size and position of the supraoccipital crest and the distance to the interopercle–subopercle junction. Cranial variation among species was related to phylogeny. To better understand the evolution of cranial morphology, it is necessary to evaluate the morphofunctional relationship of other anatomical structures related to feeding, as well as to increase the number of study species in each ecomorph by including other lineages.
TL;DR: In this article , the authors used a multimodal approach, including microcomputed tomography and scanning electron microscopy (SEM), to visualize and describe the variability in baleen anatomy across five species of rorqual whales, spanning two orders of magnitude in body length.
Abstract: Filter‐feeding has been present for hundreds of millions of years, independently evolving in aquatic vertebrates' numerous times. Mysticete whales are a group of gigantic, marine filter‐feeders that are defined by their fringed baleen and are divided into two groups: balaenids and rorquals. Recent studies have shown that balaenids likely feed using a self‐cleaning, cross‐flow filtration mechanism where food particles are collected and then swept to the esophagus for swallowing. However, it is unclear how filtering is achieved in the rorquals (Balaenopteridae). Lunging rorqual whales engulf enormous masses of both prey and water; the prey is then separated from the water through baleen plates lining the length of their upper jaw and positioned perpendicular to flow. Rorqual baleen is composed of both major (larger) and minor (smaller) keratin plates containing embedded fringe that extends into the whale's mouth, forming a filtering fringe. We used a multimodal approach, including microcomputed tomography (µCT) and scanning electron microscopy (SEM), to visualize and describe the variability in baleen anatomy across five species of rorqual whales, spanning two orders of magnitude in body length. For most morphological measurements, larger whales exhibited hypoallometry relative to body length. µCT and SEM revealed that the major and minor plates break away from the mineralized fringes at variable distances from the gums. We proposed a model for estimating the effective pore size to determine whether flow scales with body length or prey size across species. We found that pore size is likely not a proxy for prey size but instead, may reflect changes in resistance through the filter that affect fluid flow.
TL;DR: In this paper , the authors compared two shape complexity metrics, alpha shapes and ariaDNE, in 32 species of Musteloidea and found that shape complexity, especially at the baculum distal tip, is associated with intromission duration.
Abstract: The penis bone, or baculum, is present in many orders of mammals, although its function is still relatively unknown, mainly due to the challenges with studying the baculum in vivo. Suggested functions include increasing vaginal friction, prolonging intromission and inducing ovulation. Since it is difficult to study baculum function directly, functional morphology can give important insights. Shape complexity techniques, in particular, are likely to offer a useful metric of baculum morphology, especially since finding homologous landmarks on such a structure is challenging. This study focuses on measuring baculum shape complexity in the Musteloidea—a large superfamily spanning a range of body sizes with well‐developed, qualitatively diverse bacula. We compared two shape complexity metrics—alpha shapes and ariaDNE and conducted analyses over a range of six different coefficients, or bandwidths, in 32 species of Musteloidea. Overall, we found that shape complexity, especially at the baculum distal tip, is associated with intromission duration using both metrics. These complexities can include hooks, bifurcations and other additional projections. In addition, alpha shapes complexity was also associated with relative testes mass. These results suggest that post‐copulatory mechanisms of sexual selection are probably driving the evolution of more complex‐shaped bacula tips in Musteloidea and are likely to be especially involved in increasing intromission duration during copulation.
TL;DR: In this article , a detailed comparative description of the intrinsic musculature and osteology of the pectoral free rays in three families of scorpaenoid fishes (Hoplichthyidae, Triglidae, and Synanceiidae) is presented.
Abstract: Free rays are ventral pectoral fin rays (lepidotrichia) that are free of the pectoral fin webbing. They are some of the most striking adaptations of benthic fishes. Free rays are used for specialized behaviors such as digging, walking or crawling along the sea bottom. Studies of pectoral free rays have focused on a small number of species, most notably the searobins (Family Triglidae). Previous research on the morphology of the free rays has emphasized their functional novelty. We hypothesize that the more extreme specializations of the pectoral free rays in searobins are not precisely novel, but are part of a broader range of morphological specializations that are associated with the pectoral free rays in suborder Scorpaenoidei. We perform a detailed comparative description of the intrinsic musculature and osteology of the pectoral free rays in three families of scorpaenoid fishes: Hoplichthyidae, Triglidae, and Synanceiidae. These families vary in the number of pectoral free rays and the degree of morphological specialization of those rays. As part of our comparative analysis, we propose significant revisions to earlier descriptions of both the identity and function of the musculature associated with the pectoral free rays. We focus particularly on the specialized adductors that are important for walking behaviors. Our emphasis on the homology of these features provides important morphological and evolutionary context for understanding the evolution and function of free rays within Scorpaenoidei and other groups.
TL;DR: The main cannabinoid receptor CB1R first shows expression during early neurula stage in chicken (Gallus gallus) embryos, and at early tailbud stage in the frog (Xenopus laevis) embryos as mentioned in this paper .
Abstract: The main cannabinoid receptor CB1R first shows expression during early neurula stage in chicken (Gallus gallus) embryos, and at early tailbud stage in the frog (Xenopus laevis) embryos. This raises the question of whether CB1R regulates similar or distinct processes during the embryonic development of these two species. Here, we examined whether CB1R influences the migration and morphogenesis of neural crest cells and derivatives in both chicken and frog embryos. Early neurula stage chicken embryos were exposed to arachidonyl-2'-chloroethylamide (ACEA; a CB1R agonist), N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251; a CB1R inverse agonist) or Blebbistatin (nonmuscle Myosin II inhibitor) in ovo and examined during migration of neural crest cells and at condensing cranial ganglia stage. Early tailbud stage frog embryos were bathed in ACEA, AM251 or Blebbistatin, and analyzed at late tailbud stage for changes in craniofacial and eye morphogenesis, and in patterning and morphology of melanophores (neural crest-derived pigment cells). In chicken embryos exposed to ACEA and Myosin II inhibitor, cranial neural crest cells migrated erratically from the neural tube, and the right, but not the left, ophthalmic nerve of the trigeminal ganglia was affected in ACEA- and AM251-treated embryos. In frog embryos with inactivation or activation of CB1R, or inhibition of Myosin II, the craniofacial and eye regions were smaller and/or less developed, and the melanophores overlying the posterior midbrain were more dense, and stellate in morphology, than the same tissues and cells in control embryos. This data suggests that despite differences in the time of onset of expression, normal activity of CB1R is required for sequential steps in migration and morphogenesis of neural crest cells and derivatives in both chicken and frog embryos. In addition, CB1R may signal through Myosin II to regulate migration and morphogenesis of neural crest cells and derivatives in chicken and frog embryos.
TL;DR: In this paper , the development of the mesoderm in lamprey embryos was investigated using a plasmodial sectioning and transmission electron microscopy analysis, and it was shown that during the early pharyngeal stages, the sigmoid cells transformed from the lateral plate to more caudal regions.
Abstract: Vertebrate paired appendages are one of the most important evolutionary novelties in vertebrates. During embryogenesis, the skeletal elements of paired appendages differentiate from the somatic mesoderm, which is a layer of lateral plate mesoderm. However, the presence of the somatic mesoderm in the common ancestor of vertebrates has been controversial. To address this problem, it is necessary but insufficient to understand the developmental process of lateral plate mesoderm formation in lamprey (jawless vertebrates) embryos. Here, I show the presence of the somatic mesoderm in lamprey (Lethenteron camtschaticum) embryos using plastic sectioning and transmission electron microscopy analysis. During the early pharyngeal stages, the somatic mesoderm transforms from the lateral plate mesoderm in the trunk region. Soon after, when the cardiac structures were morphologically distinct, the somatic mesoderm was recognized through the cardiac to more caudal regions. These findings indicated that the somatic mesoderm evolved before the emergence of paired appendages. I also discuss the developmental changes in the body wall organization in the common ancestor of vertebrates, which is likely related to the evolution of the paired appendages.
TL;DR: In this article , the authors compared the muscle architecture of scratch-digging Cape dune mole-rat (Bathyergus suillus) and chisel-toothed naked mole rat (Heterocephalus glaber) and found that the forelimb muscles involved with the power stroke of digging (limb retractors and scapula elevators) showed higher muscle mass percentage, force output and shortening capacity compared to those in H. glaber.
Abstract: The scratch‐digging Cape dune mole‐rat (Bathyergus suillus), and the chisel‐toothed digging naked mole‐rat (Heterocephalus glaber) are African mole‐rats that differ in their digging strategy. The aim of this study was to determine if these behavioural differences are reflected in the muscle architecture and fibre‐type composition of the forelimb muscles. Muscle architecture parameters of 39 forelimb muscles in both species were compared. Furthermore, muscle fibre type composition of 21 forelimb muscles were analysed using multiple staining protocols. In B. suillus, muscles involved with the power stroke of digging (limb retractors and scapula elevators), showed higher muscle mass percentage, force output and shortening capacity compared to those in H. glaber. Additionally, significantly higher percentages of glycolytic fibres were observed in the scapular elevators and digital flexors of B. suillus compared to H. glaber, suggesting that the forelimb muscles involved in digging in B. suillus provide fast, powerful motions for effective burrowing. In contrast, the m. sternohyoideus a head and neck flexor, had significantly more oxidative fibres in H. glaber compared to B. suillus. In addition, significantly greater physiological cross‐sectional area and fascicle length values were seen in the neck flexor, m. sternocleidomastoideus, in H. glaber compared to B. suillus, which indicates a possible adaptation for chisel‐tooth digging. While functional demands may play a significant role in muscle morphology, the phylogenetic differences between the two species may play an additional role which needs further study.
TL;DR: In this article , the microvascular anatomy of choriocapillaris, iris, ciliary body, and superficial vascular hyaloid system of Xenopus laevis was studied by scanning electron microscopy of vascular casts.
Abstract: The microvascular anatomy of choriocapillaris, iris, ciliary body, and superficial vascular hyaloid system of eyes was studied in the permanent aquatic Xenopus laevis by scanning electron microscopy of vascular casts and was compared with that published in two semiaquatic ranid species (Rana esculenta and Rana temporaria), and the urodelian species Triturus criststus carnifex. Results showed that the choriocapillaris in Xenopus consisted of a dense meshwork of wide capillaries displaying polygonal arrays at the scleral side with venules leaving the centers and arterioles supplied from the periphery. The choriocapillaris lacked the multilayered capillary meshwork described in ranids. Iris and ciliary body were supplied by nasal and temporal branches of the iridial artery, which either originated with a common stem from the hyaloid artery or arose as individual vessels from the proximal portions of the semicircular nasal and temporal branches of the hyaloid artery. These branches ran in the pupillary margin and supplied the two‐dimensional capillary network of the iris, as well as the three‐dimensional network of the ciliary body. Iris and ciliary body drained via parallel running vasa recta into the choriocapillaris. The superficial vascular hyaloid bed (system) was supplied by the hyaloid artery. This artery coursed along the scleral surface of the ventrotemporal choriocapillaris toward the ora serrata, where it bifurcated into a temporal and a nasal semicircular branch. Seven to 10 arterial meridional twigs arose from these branches and supplied the superficial hyaloid capillary bed. Capillaries drained into branches of the hyaloid vein, which ascended toward the ora serrata, where the hyaloid vein joined the temporal branch of the ciliary vein.
TL;DR: In this article , the authors investigated whether female Allegheny crayfish, Faxonius obscurus, claws change in size, shape, or pinching strength based on whether a female is in a reproductive or non-reproductive form.
Abstract: Animal weapons are morphological traits that improve the fighting ability of the wielder and are associated with competition. These traits are typically sexually dimorphic, with males possessing weaponry and females lacking weaponry. However, in some cases, like in many crustaceans, both males and females wield enlarged claws, which may function as weapons. Further, animal weapons may vary in their size, shape, and performance, with theory predicting that selection pressure for weaponry should be the highest when the importance of fights is the greatest, such as during a reproductive season. However, the degree and direction of selection may vary based on sex and season, with females potentially benefiting from wielding larger weapons during nonreproductive seasons. Crayfishes offer an ideal system to investigate how weapon phenotypes change across reproductive seasons since both males and females undergo a form alteration associated with reproduction. Thus, we investigated whether female Allegheny crayfish, Faxonius obscurus, claws change in size, shape, or pinching strength based on whether a female is in a reproductive or nonreproductive form. We found that female F. obscurus claws are larger and stronger during the reproductive season. These findings align with previous research on males of the same species. We discuss how predictions about the relationship between seasonality and weapon investment may differ based on sex.
TL;DR: In this paper , the authors focus on the link between morphological traits and locomotor behavior such as terrestriality, fossoriality and arboreality (including gliding).
Abstract: The study of morphological adaptations to different ecological parameters among fossil vertebrates has been an important challenge in recent decades. In this paper, we focus on the link between morphological traits and locomotor behavior such as terrestriality, fossoriality and arboreality (including gliding). One of the most diverse groups in which various locomotor habits are represented is rodents, occupying a wide range of ecological niches. This work highlights morphological variations in skulls and humerus in extant rodents with varying locomotion, to predict this parameter in the extinct species Diamantomys luederitzi (Early Miocene, Napak, Uganda). Linear discriminant analysis and phylogenetic flexible discriminant analysis are used to analyze datasets obtained via traditional morphometry (measurements) and geometric morphometrics (landmarks). The results show good discrimination between locomotor groups for both structures in extant species: the skull has a wider and longer rostrum in terrestrial and fossorial taxa compared to arboreal rodents, is also higher and posteriorly wider in fossorial taxa; the distal humerus shows elongation of the trochlea and capitulum and a higher trochlea in fossorial and terrestrial species, allowing an increase of stability instead of mobility, which is more important in arboreal taxa for movement in trees. In D. luederitzi, all skull analyses except one predicted it as a terrestrial species, the other prediction as a glider was possibly linked to the diet. For the distal humerus, this species has been predicted as a terrestrial, fossorial and arboreal taxon in differing analyses, reflected by morphological traits represented in these different locomotor categories. These varying predictions could highlight the intraspecific variation in this fossil species as well as its locomotor repertoire, raising a discussion about the use of different methods in such analyses. In addition to these predictions, several issues are discussed, such as the presence of locomotor signal in the skull and its validity in locomotor studies, as well as the relevance of the use of fragmentary material in such analyses. The results obtained in this work highlight the importance of the locomotor signal in these structures, as well as the possibility of taking into account poorly preserved material, in particular the distal humerus.
TL;DR: In a survey of extant benthic shell-bearing molluscs, the authors document imbricated sculpture primarily in epifaunal bivalves or on the exposed sectors of shells of semi-infaunal Bivalves.
Abstract: Molluscan shells display a high diversity of external sculpture. Sculptural elements may be symmetrical, where both edges of an element are morphologically similar, or asymmetrical, where one edge is steeper than the other. Asymmetrical sculpture can be ratcheted, with the leading edges (those in the direction of locomotion or growth) less steep than the trailing edges, or imbricated (leading edges steeper than trailing edges). While the ratcheted sculpture is better known, the diversity of imbricated sculpture has remained largely unexplored. In a survey of extant benthic shell‐bearing molluscs, we document imbricated sculpture primarily in epifaunal bivalves or on the exposed sectors of shells of semi‐infaunal bivalves. Imbricated sculpture is particularly widespread in pteriomorphian bivalves, but it is absent in the subclade Mytiloidea as well as in highly mobile Pectinidae. It also occurs in many carditid bivalves (Archiheterodonta) and in phylogenetically scattered euheterodonts. In several infaunal bivalves including species of Cardites (Carditidae), Hecuba (Donacidae), and Chione (Veneridae), comarginal elements on the posterior sector are imbricated whereas anterior comarginal ridges are ratcheted. Imbricated sculpture in bivalves tends to be concentrated on the upper (left) valves of pectinids or on the posterior sector of both valves in archiheterodonts and euheterodonts. Imbricated sculpture is uncommon in gastropods, even in epifaunal species, but does occur in the collabral ridges in some Vasidae and a few other groups. Expression of imbricated sculpture does not depend on shell mineral composition or microstructure. The ecological distribution and within‐shell pattern of expression of imbricated sculpture point to the likelihood that this type of asymmetrical sculpture is both widespread and potentially functional. Additionally, we present a potential methodology whereby shell sculpture categories (symmetrical, ratcheted, and imbricated) may be quantified by comparing the lengths of corresponding leading and trailing edges across the shell surface.
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TL;DR: The Journal of Morphology Volume 284, Issue 6 e21592 ISSUE INFORMATIONFree Access Issue Information First published: 16 April 2023 https://doi.org/10.1002/jmor.21592 as discussed by the authors
Abstract: Journal of MorphologyVolume 284, Issue 6 e21592 ISSUE INFORMATIONFree Access Issue Information First published: 16 April 2023 https://doi.org/10.1002/jmor.21592AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume284, Issue6June 2023e21592 RelatedInformation