Tetrapod Vertebrates Research Articles

Convergent evolution toward a slow pace of life predisposes insular endotherms to anthropogenic extinctions.

Island vertebrates have evolved a number of morphological, physiological, and life history characteristics that set them apart from their mainland relatives. However, to date, the evolution of metabolism and its impact on the vulnerability to extinction of insular vertebrates remains poorly understood. This study used metabolic data from 2813 species of tetrapod vertebrates, including 695 ectothermic and 2118 endothermic species, to reveal that island mammals and birds evolved convergent metabolic strategies toward a slow pace of life. Insularity was associated with shifts toward slower metabolic rates and greater generation lengths in endotherms, while insularity just drove the evolution of longer generation lengths in ectotherms. Notably, a slow pace of life has exacerbated the extinction of insular endemic species in the face of anthropogenic threats. These findings have important implications for understanding physiological adaptations associated with the island syndrome and formulating conservation strategies across taxonomic groups with different metabolic modes.

The genomic evolution of visual opsin genes in amphibians

Among tetrapod (terrestrial) vertebrates, amphibians remain more closely tied to an amphibious lifestyle than amniotes, and their visual opsin genes may be adapted to this lifestyle. Previous studies have discussed physiological, morphological, and molecular changes in the evolution of amphibian vision. We predicted the locations of the visual opsin genes, their neighboring genes, and the tuning sites of the visual opsins, in 39 amphibian genomes. We found that all of the examined genomes lacked the Rh2 gene. The caecilian genomes have further lost the SWS1 and SWS2 genes; only the Rh1 and LWS genes were retained. The loss of the SWS1 and SWS2 genes in caecilians may be correlated with their cryptic lifestyles. The opsin gene syntenies were predicted to be highly similar to those of other bony vertebrates. Moreover, dual syntenies were identified in allotetraploid Xenopus laevis and X. borealis. Tuning site analysis showed that only some Caudata species might have UV vision. In addition, the S164A that occurred several times in LWS evolution might either functionally compensate for the Rh2 gene loss or fine-tuning visual adaptation. Our study provides the first genomic evidence for a caecilian LWS gene and a genomic viewpoint of visual opsin genes by reviewing the gains and losses of visual opsin genes, the rearrangement of syntenies, and the alteration of spectral tuning in the course of amphibians’ evolution.

Salamanders aid research into mechanisms of non‐canonical organ regeneration for clinical applications

AbstractSalamanders possess remarkable regenerative capacities for organ regeneration among tetrapod vertebrates. Previous research has primarily focused on studying the regeneration of canonical tissues or organs such as limbs, tail, brain, spinal cord, heart, and lens. The advancements made in these areas have broader implications for understanding regeneration and developing therapeutic approaches for these organs, not only in salamanders but also in other vertebrates. In recent years, there has been an increasing interest in studying the regeneration of non‐canonical organs in salamanders, such as the liver, lungs, kidneys, and pancreas. This diversification of research has opened up new avenues and provided potential solutions to challenging clinical problems. This review aims to summarize the progress made in the field of non‐canonical organ regeneration in salamanders and provides an outlook on future research directions.

Functional diversity of snake locomotor behaviors: A review of the biological literature for bioinspiration.

Organismal solutions to natural challenges can spark creative engineering applications. However, most engineers are not experts in organismal biology, creating a potential barrier to maximally effective bioinspired design. In this review, we aim to reduce that barrier with respect to a group of organisms that hold particular promise for a variety of applications: snakes. Representing >10% of tetrapod vertebrates, snakes inhabit nearly every imaginable terrestrial environment, moving with ease under many conditions that would thwart other animals. To do so, they employ over a dozen different types of locomotion (perhaps well over). Lacking limbs, they have evolved axial musculoskeletal features that enable their vast functional diversity, which can vary across species. Different species also have various skin features that provide numerous functional benefits, including frictional anisotropy or isotropy (as their locomotor habits demand), waterproofing, dirt shedding, antimicrobial properties, structural colors, and wear resistance. Snakes clearly have much to offer to the fields of robotics and materials science. We aim for this review to increase knowledge of snake functional diversity by facilitating access to the relevant literature.

Morphogenetic processes in the development and evolution of the arteries of the pharyngeal arches: their relations to congenital cardiovascular malformations.

The heart and aortic arch arteries in amniotes form a double circulation, taking oxygenated blood from the heart to the body and deoxygenated blood to the lungs. These major vessels are formed in embryonic development from a series of paired and symmetrical arteries that undergo a complex remodelling process to form the asymmetric arch arteries in the adult. These embryonic arteries form in the pharyngeal arches, which are symmetrical bulges on the lateral surface of the head. The pharyngeal arches, and their associated arteries, are found in all classes of vertebrates, but the number varies, typically with the number of arches reducing through evolution. For example, jawed vertebrates have six pairs of pharyngeal arch arteries but amniotes, a clade of tetrapod vertebrates, have five pairs. This had led to the unusual numbering system attributed to each of the pharyngeal arch arteries in amniotes (1, 2, 3, 4, and 6). We, therefore, propose that these instead be given names to reflect the vessel: mandibular (1st), hyoid (2nd), carotid (3rd), aortic (4th) and pulmonary (most caudal). Aberrant arch artery formation or remodelling leads to life-threatening congenital cardiovascular malformations, such as interruption of the aortic arch, cervical origin of arteries, and vascular rings. We discuss why an alleged fifth arch artery has erroneously been used to interpret congenital cardiac lesions, which are better explained as abnormal collateral channels, or remodelling of the aortic sac.

Deciphering locomotion in reptiles: application of elliptic Fourier transforms to femoral microanatomy

Abstract Reptiles represent one of the most diverse groups of tetrapod vertebrates. Extant representatives of reptiles include lepidosaurs (lizards), testudines (turtles) and archosaurs (crocodiles and birds). In particular, they show an important locomotor diversity with bipedal, quadrupedal and facultatively bipedal taxa. This diversity is accompanied by substantial microanatomical disparity in the limb bones. Although many studies have highlighted the link between locomotion and bone microstructure, the latter has never been quantitatively studied from an angular perspective. Indeed, some taxa show microanatomical heterogeneity in cross-section. Here we show, using elliptic Fourier transforms and statistical analyses integrating phylogeny, how angular microanatomical parameters measured on reptilian femoral cross-sections, such as angular bone compactness, can be related to locomotion in this clade. Although phylogeny appears to have a significant impact on our results, we show that a functional signal exists. In particular, we show that bipeds and quadrupeds present a craniolateral-caudomedial and dorsoventral deficit in bone compactness, respectively. This reflects cross-sectional eccentricity in these directions that we relate to the forces acting upon the femur in different postural contexts. This work contributes to deciphering the complex interplay between phylogeny, femoral cross-sectional microanatomy and locomotion in reptiles.

Origin of the propatagium in non-avian dinosaurs

Avian wings as organs for aerial locomotion are furnished with a highly specialized musculoskeletal system compared with the forelimbs of other tetrapod vertebrates. Among the specializations, the propatagium, which accompanies a skeletal muscle spanning between the shoulder and wrist on the leading edge of the wing, represents an evolutionary novelty established at a certain point in the lineage toward crown birds. However, because of the rarity of soft-tissue preservation in the fossil record, the evolutionary origin of the avian propatagium has remained elusive. Here we focus on articulated skeletons in the fossil record to show that angles of elbow joints in fossils are indicators of the propatagium in extant lineages of diapsids (crown birds and non-dinosaurian diapsids), and then use this relationship to narrow down the phylogenetic position acquiring the propatagium to the common ancestor of maniraptorans. Our analyses support the hypothesis that the preserved propatagium-like soft tissues in non-avian theropod dinosaurs (oviraptorosaurian Caudipteryx and dromaeosaurian Microraptor) are homologous with the avian propatagium, and indicate that all maniraptoran dinosaurs likely possessed the propatagium even before the origin of flight. On the other hand, the preserved angles of wrist joints in non-avian theropods are significantly greater than those in birds, suggesting that the avian interlocking wing-folding mechanism involving the ulna and radius had not fully evolved in non-avian theropods. Our study underscores that the avian wing was acquired through modifications of preexisting structures including the feather and propatagium.

Locomotor and postural diversity among reptiles viewed through the prism of femoral microanatomy: Palaeobiological implications for some Permian and Mesozoic taxa.

The water-to-land transition by the first tetrapod vertebrates represents a key stage in their evolution. Selection pressures exerted by this new environment on animals led to the emergence of new locomotor and postural strategies that favoured access to different ecological niches and contributed to their evolutionary success. Today, amniotes show great locomotor and postural diversity, particularly among Reptilia, whose extant representatives include parasagittally locomoting erect and crouched bipeds (birds), sub-parasagittal 'semi-erect' quadrupeds (crocodylians) and sprawling quadrupeds (squamates and turtles). But the different steps leading to such diversity remain enigmatic and the type of locomotion adopted by many extinct species raises questions. This is notably the case of certain Triassic taxa such as Euparkeria and Marasuchus. The exploration of the bone microanatomy in reptiles could help to overcome these uncertainties. Indeed, this locomotor and postural diversity is accompanied by great microanatomical disparity. On land, the bones of the appendicular skeleton support the weight of the body and are subject to multiple constraints that partly shape their external and internal morphology. Here we show how microanatomical parameters measured in cross-section, such as bone compactness or the position of the medullocortical transition, can be related to locomotion. We hypothesised that this could be due to variations in cortical thickness. Using statistical methods that take phylogeny into account (phylogenetic flexible discriminant analyses), we develop different models of locomotion from a sample of femur cross-sections from 51 reptile species. We use these models to infer locomotion and posture in 7 extinct reptile taxa for which they remain debated or not fully clear. Our models produced reliable inferences for taxa that preceded and followed the quadruped/biped and sprawling/erect transitions, notably within the Captorhinidae and Dinosauria. For taxa contemporary with these transitions, such as Terrestrisuchus and Marasuchus, the inferences are more questionable. We use linear models to investigate the effect of body mass and functional ecology on our inference models. We show that body mass seems to significantly impact our model predictions in most cases, unlike the functional ecology. Finally, we illustrate how taphonomic processes can impact certain microanatomical parameters, especially the eccentricity of the section, while addressing some other potential limitations of our methods. Our study provides insight into the evolution of enigmatic locomotion in various early reptiles. Our models and methods could be used by palaeontologists to infer the locomotion and posture in other extinct reptile taxa, especially when considered in combination with other lines of evidence.

Molecular Ecology of Freshwater Turtles and Future directions

The distribution and diversity of turtles now reflect the lengthy and complex evolution of the taxonomy, which represents an old group of tetrapod vertebrates in terms of evolutionary history. Freshwater turtles represent the majority of the 365 species, and they mostly live in tropical and subtropical regions. Emydidae diversity hotspots can be found in Southeast North America, as can Geoemydidae and Trionychidae in the Indo-Malayan area. While Pelomedusidae are mostly found in Africa, Chelidae are primarily found in the Neotropics and Australia. Most species of the genus are endemic to a particular region or even to a single location. The majority of freshwater turtles suffer varied degrees of threat, mostly from habitat changes and collection. With the use of morphological and molecular data, the majority of phylogenetic trees for different turtle species have been generated using DNA techniques and procedures. The complete mitochondrial DNA (mtDNA), dehydrogenase subunit 4 (ND4), cytochrome b (Cyt b), carapacial ridge (CR), and cytochrome c oxidase subunit I (CO I) genes of freshwater turtles were sequenced by using universal PCR and long-PCR methods. Along with CR sequences of freshwater turtles, the composition and structure of the control region of diverse species were compared and analysed. Functional domains in the regulatory area, as well as their conserved sequences, were determined based on sequence similarities to other turtles. The mitochondrial regulatory regions and flanking sequences of diverse freshwater turtle species were recovered using Long-PCR and gene-specific primers. To clarify the genetic links between the fresh water turtle species that share the same habitat type, a tree was created based on Cytochrome b sequencing data and the PCR- Restriction fragment length polymorphism (RFLP) pattern. Keywords: Complex evolution, Phylogenetics, Phylogenomics, Tetrapod vertebrates

Effects of visitor disturbance on tetrapod vertebrates in the Horton Plains National Park, Sri Lanka

Effect of visitor disturbances on tetrapod vertebrates was studied from December 2017 to October 2018 in the Horton Plains National Park (HPNP), which is one of the world’s best nature reserves and a popular tourist destination of Sri Lanka. Roads and nature trails with cloud forest, aquatic and grasslands habitats inside the HPNP were selected to compare the effect of visitor disturbances. Three 100 meter fixed length line transects were marked along the roads and the nature trails in each habitat. Vehicle noise was measured using sound meter software. Visitor activities that cause disturbance included road kills, photography, trampling and animal feeding. Amphibian and reptile road kills were higher compared to other tetrapod road kills during vacation periods. Behavioral response of species to visitor disturbances included avoidance, habituation and attraction. When the vehicle noise range was from 63±2.11 dB to 69±2.11 dB, habituation behavior was displayed. When the vehicle noise range increased to the range of 70±4.71 dB to 88±4.71 dB, avoidance behavior was displayed. Animals display a propensity to habituation behavior compared to avoidance behavior when vehicle speed was less than 30 kmh/hr. The results of this study can be used to integrate with the future visitor, park and wildlife management practices of the park.

Influence of recreational trails on species diversity of tetrapod vertebrates within the Horton Plains National Park, Sri Lanka

Influence of recreational trails on species diversity of tetrapod vertebrates within the Horton Plains National Park, Sri Lanka

Heart Position is Associated with Vertebral Regionalization in Two Species of Garter Snakes (Thamnophis)

A long-standing question regarding the evolution of the snake body plan is to what extent does axial regionalization and organ position correspond with that of generalized tetrapod vertebrates. Here, we evaluated the position of shifts in vertebral morphology with respect to heart location in 2 species and 13 specimens of garter snakes (Thamnophis). From dissections, geometric morphometrics, and segmented regressions on principal component scores describing shape of the cranial aspect of vertebrae, we determined a consistent morphological transition at approximately 17% of the pre-cloacal vertebral column. The transition was strongly coincident with the position of the heart, suggesting a developmental link between the first major transition in vertebral regions and the longitudinal position of the heart in garter snakes. Our novel discovery has implications for further recognizing the pre-cloacal vertebral column of snakes as regionalized, and that these regions are positionally linked with organogenesis of the viscera.

SPERM FACTORS AND EGG ACTIVATION: Divergent sperm factors for egg activation in amphibian fertilization.

Mature amphibian eggs arrested at meiotic metaphase II must undergo activation to initiate embryonic development soon after fertilization. Fertilizing sperm provide eggs with a signal that induces egg activation, and an increase in intracellular Ca2+ concentration in the egg cytoplasm (a Ca2+ rise) is the most important signal for this initiation. The sperm transmits the signal for the Ca2+ rise, known as the sperm factor, which is divergent between anurans and urodeles. In monospermic anurans, the sperm transmits the signal through a receptor on the egg membrane, causing a single rapid Ca2+ rise. Sperm matrix metalloproteinase-2 is a potential candidate for the receptor-mediated sperm factor in anurans. In physiologically polyspermic urodeles, multiple slower Ca2+ rises are caused by a soluble sperm factor (sperm-specific citrate synthase) which is transferred to the egg cytoplasm after sperm-egg fusion. We discuss the molecular mechanisms of egg activation in amphibian fertilization, focusing on recent progress in characterizing these sperm factors and their divergence during the evolution of tetrapod vertebrates.

Macroecology of reproductive modes in the diverse anuran fauna of the Brazilian Atlantic Forest

Anurans exhibit the widest variety of reproductive modes among tetrapod vertebrates. The Atlantic Forest is a hotspot for biological conservation; however, biogeographic documentation of the richness of anuran reproductive modes are underexplored. By overlaying maps of 249 species having reproductive modes with aquatic eggs and 101 species with non-aquatic eggs, we described the geographical patterns of anuran reproductive modes in the Atlantic Forest and identified the main correlates of reproductive diversity of these two major types of anuran reproduction. We found the greatest diversity of reproductive modes in the coastal region of the Atlantic Forest, whereas a smaller number of reproductive modes was found in inland regions of the hotspot. These regions are broadly characterized by deciduous/semideciduous forests and a warmer and more seasonal climate regime in southeastern and southern Brazil. In this climatically harsher region, reproductive modes were more basal and generalized in anurans. Correlative analyses showed that the richness of reproductive modes with aquatic eggs can be described by general combinations of climate, topography, and vegetation types, whereas larger numbers of reproductive modes with non-aquatic eggs are better described by specific variables of temperature seasonality, amount of ombrophilous forests, and rugged topography. The predictors identified here are environmental variables that should be continuously monitored in situ; identifying threshold values that could lead a species to a critical conservation status is key to efficiently protecting the rich anuran fauna of the Atlantic Forest.

Novel Expansion of Matrix Metalloproteases in the Laboratory Axolotl (Ambystoma mexicanum) and Other Salamander Species

Matrix metalloprotease (MMP) genes encode endopeptidases that cleave protein components of the extracellular matrix (ECM) as well as non-ECM proteins. Here we report the results of a comprehensive survey of MMPs in the laboratory axolotl and other representative salamanders. Surprisingly, 28 MMPs were identified in salamanders and 9 MMP paralogs were identified as unique to the axolotl and other salamander taxa, with several of these presenting atypical amino acid insertions not observed in other tetrapod vertebrates. Furthermore, as assessed by sequence information, all of the novel salamander MMPs are of the secreted type, rather than cell membrane anchored. This suggests that secreted type MMPs expanded uniquely within salamanders to presumably execute catalytic activities in the extracellular milieu. To facilitate future studies of salamander-specific MMPs, we annotated transcriptional information from published studies of limb and tail regeneration. Our analysis sets the stage for comparative studies to understand why MMPs expanded uniquely within salamanders.

Evolution of touch and proprioception of the limbs: Insights from fish and humans.

The function of the hands is inextricably linked to cutaneous mechanosensation, both in touch and in how hand movement and posture (proprioception) are controlled. The structure and behavior of hands and distal forelimbs of other vertebrates have been evolutionarily shaped by these mechanosensory functions. The distal forelimb of tetrapod vertebrates is homologous to the pectoral fin rays and membrane of fishes. Fish fins demonstrate similar mechanosensory abilities to hands and other distal tetrapod forelimbs in touch and proprioception. These results indicate that vertebrates were using the core mechanosensory inputs, such as fast adapting and slow adapting nerve responses, to inform fin and limb function and behavior before their diversification in fish and tetrapod lineages.

Pharmacological modulation of the cAMP signaling of two isoforms of melanocortin-3 receptor by melanocortin receptor accessory proteins in the tetrapod Xenopus laevis.

As a member of the seven-transmembrane rhodopsin-like G protein-coupled receptor superfamily, the melanocortin-3 receptor (MC3R) is vital for the regulation of energy homeostasis and rhythms synchronizing in mammals, and its pharmacological effect could be directly influenced by the presence of melanocortin receptor accessory proteins (MRAPs), MRAP1 and MRAP2. The tetrapod amphibian Xenopus laevis (xl) retains higher duplicated genome than extant teleosts and serves as an ideal model system for embryonic development and physiological studies. However, the melanocortin system of the Xenopus laevis has not yet been thoroughly evaluated. In this work, we performed sequence alignment, phylogenetic tree, and synteny analysis of two xlMC3Rs. Co-immunoprecipitation and immunofluorescence assay further confirmed the co-localization and in vitro interaction of xlMC3Rs with xlMRAPs on the plasma membrane. Our results demonstrated that xlMRAP2.L/S could improve α-MSH-stimulated xlMC3Rs signaling and suppress their surface expression. Moreover, xlMC3R.L showed a similar profile on the ligands and surface expression in the presence of xlMRAP1.L. Overall, the distinct pharmacological modulation of xlMC3R.L and xlMC3R.S by dual MRAP2 proteins elucidated the functional consistency of melanocortin system during genomic duplication of tetrapod vertebrates.

Genetic basis for an evolutionary shift from ancestral preaxial to postaxial limb polarity in non-urodele vertebrates

In most tetrapod vertebrates, limb skeletal progenitors condense with postaxial dominance. Posterior elements (such as ulna and fibula) appear prior to their anterior counterparts (radius and tibia), followed by digit-appearance order with continuing postaxial polarity. The only exceptions are urodele amphibians (salamanders), whose limb elements develop with preaxial polarity and who are also notable for their unique ability to regenerate complete limbs as adults. The mechanistic basis for this preaxial dominance has remained an enigma and has even been proposed to relate to the acquisition of novel genes involved in regeneration. However, recent fossil evidence suggests that preaxial polarity represents an ancestral rather than derived state. Here, we report that 5'Hoxd (Hoxd11-d13) gene deletion in mouse is atavistic and uncovers an underlying preaxial polarity in mammalian limb formation. We demonstrate this shift from postaxial to preaxial dominance in mouse results from excess Gli3 repressor (Gli3R) activity due to the loss of 5'Hoxd-Gli3 antagonism and is associated with cell-cycle changes promoting precocious cell-cycle exit in the anterior limb bud. We further show that Gli3 knockdown in axolotl results in a shift to postaxial dominant limb skeleton formation, as well as expanded paddle-shaped limb-bud morphology and ensuing polydactyly. Evolutionary changes in Gli3R activity level, which also played a key role in the fin-to-limb transition, appear to be fundamental to the shift from preaxial to postaxial polarity in formation of the tetrapod limb skeleton.

Two Functional Epithelial Sodium Channel Isoforms Are Present in Rodents despite Pronounced Evolutionary Pseudogenization and Exon Fusion.

The epithelial sodium channel (ENaC) plays a key role in salt and water homeostasis in tetrapod vertebrates. There are four ENaC subunits (α, β, γ, δ), forming heterotrimeric αβγ- or δβγ-ENaCs. Although the physiology of αβγ-ENaC is well understood, for decades the field has stalled with respect to δβγ-ENaC due to the lack of mammalian model organisms. The SCNN1D gene coding for δ-ENaC was previously believed to be absent in rodents, hindering studies using standard laboratory animals. We analyzed all currently available rodent genomes and discovered that SCNN1D is present in rodents but was independently lost in five rodent lineages, including the Muridae (mice and rats). The independent loss of SCNN1D in rodent lineages may be constrained by phylogeny and taxon-specific adaptation to dry habitats, however habitat aridity does not provide a selection pressure for maintenance of SCNN1D across Rodentia. A fusion of two exons coding for a structurally flexible region in the extracellular domain of δ-ENaC appeared in the Hystricognathi (a group that includes guinea pigs). This conserved pattern evolved at least 41 Ma and represents a new autapomorphic feature for this clade. Exon fusion does not impair functionality of guinea pig (Cavia porcellus) δβγ-ENaC expressed in Xenopus oocytes. Electrophysiological characterization at the whole-cell and single-channel level revealed conserved biophysical features and mechanisms controlling guinea pig αβγ- and δβγ-ENaC function as compared with human orthologs. Guinea pigs therefore represent commercially available mammalian model animals that will help shed light on the physiological function of δ-ENaC.

¿CUÁNTO CONOCEMOS DE NUESTRA FAUNA AUTÓCTONA? UN ESTUDIO SOBRE VERTEBRADOS TETRÁPODOS

From the beginning of civilization and in several cultures, people established a strong connection with animals and in many cultural traditions they have imbued them with a symbolic value. A good knowledge of the species of fauna and flora of a certain place, allows us to understand the importance of their protection and conservation, which will greatly help to face one of the main problems of humanity on a global scale: the loss of biodiversity. In recent years in Uruguay there has been an increase regarding the knowledge of the species that make up our native fauna. Although this information is recognized and accessible within the scientific-academic field, it is often not known by the rest of the population. The objective of this work is to evaluate the current state of knowledge of the fauna of native tetrapod vertebrates in the Uruguayan population, which was done through a semi-structured survey of 593 people. The results obtained showed a scarce knowledge of our fauna, a fact that has been seen in other countries. We discuss the challenge of implementing actions and strategies that favor the knowledge about it in the population.