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189 results for “squamation”
Data from: Fully-sampled phylogenies of squamates reveal evolutionary patterns in threat status
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Dataset for Ecomorphological diversification of squamates in the Cretaceous
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Data from: Squamate hatchling size and the evolutionary causes of negative offspring size allometry
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Data from: Squamate Conserved Loci (SqCL): a unified set of conserved loci for phylogenomics and population genetics of squamate reptiles
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Data from: A global test of the cold-climate hypothesis for the evolution of viviparity of squamate reptiles
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Data from: Combining phylogenomic and supermatrix approaches, and a time-calibrated phylogeny for squamate reptiles (lizards and snakes) based on 52 genes and 4162 species
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Reconstructing squamate biogeography in Afro-Arabia reveals the influence of a complex and dynamic geologic past
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Supplementary Figure 2 from "Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"
<p> </p> <p>Published as part of <a href="https://doi.org/10.1038/s41467-019-13405-w"><strong>Macrì, S <em>et al</em>., 2019, Nature Communications: 10(1):5560</strong></a></p> <p><strong>"Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"</strong> DOI: https://doi.org/10.1038/s41467-019-13405-w</p> <p> </p> <p><strong>Supplementary Fig. 2: Phylomorphospace and landmark-free geometric morphometric methods.</strong> <strong>a</strong>, <strong>b</strong>, Plots of 2D phylomorphospace (with species names indicated) showing the cerebellar (<strong>a</strong>) and whole-brain (<strong>b</strong>) shape distribution of snakes (coloured squares) and lizards (coloured circles) with different locomotor modes (see colour code in <strong>a</strong>). Numbers in brackets indicate the percentage of variance explained by each of the PC axes, and 68% confidence ellipses are shown for each locomotor mode. Asterisks in (<strong>a</strong>) mark individuals belonging to the Scincidae family. <strong>c</strong>, <strong>d</strong>, Plots of 3D morphospace obtained using landmark-free ShapeWorks (<strong>c</strong>) and GPSA (<strong>d</strong>) methods, showing the cerebellar (<strong>c</strong>) and whole-brain (<strong>d</strong>) shape distribution of snakes (coloured cubes) and lizards (coloured spheres) with different locomotor modes (see colour code in <strong>a</strong>). Numbers in brackets indicate the percentage of variance explained by each of the PC axes. The PC2 axis in (<strong>d</strong>) was inverted for better comparison with landmark-based geometric morphometric methods.</p> <p> </p> <p> </p>
Figure 5 from "Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"
<p>Published as part of <a href="https://doi.org/10.1038/s41467-019-13405-w"><strong>Macrì, S <em>et al</em>., 2019, Nature Communications: 10(1):5560</strong></a></p> <p><strong>"Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"</strong> DOI: https://doi.org/10.1038/s41467-019-13405-w</p> <p> </p> <p><strong>Fig. 5 Cerebellar shape variation in squamates with different locomotor behaviours.</strong> <strong>a</strong> 3D plot of principal component (PC) scores showing shape distribution of isolated cerebella from snakes (coloured cubes) and lizards (coloured spheres) with different locomotor modes (see colour code and symbols in bottom left corner). Numbers in brackets indicate the percentage of variance explained by each of the PC axes, and 68% confidence ellipses are shown for each locomotor mode. The 3D-rendered cerebella corresponding to extreme (indicated by coloured solid arrows, with species names) or representative (coloured dashed arrows, with species names) lizard and snake species in both positive and negative directions along the first two PCs are shown in pial (left) and lateral (right) views. <strong>b</strong> Warped surfaces of cerebellum representing the reconstructed mean shape configuration for each indicated limbless or limb-reduced (left panels) or quadrupedal (right) locomotion mode are shown in pial surface (top row) and lateral views (bottom). Colour gradient, ranging from blue to yellow, reflects the relative Procrustes distance (in μm) of shape changes from the overall mean shape for the entire dataset.</p>
Figure 4 from "Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"
<p> </p> <p>Published as part of <a href="https://doi.org/10.1038/s41467-019-13405-w"><strong>Macrì, S <em>et al</em>., 2019, Nature Communications: 10(1):5560</strong></a></p> <p><strong>"Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"</strong> DOI: https://doi.org/10.1038/s41467-019-13405-w</p> <p> </p> <p><strong>Fig. 4</strong> <strong>Morphological variation of major brain subdivisions in squamates with different locomotor behaviours.</strong> <strong>a</strong>–<strong>e</strong> 2D plots of principal component (PC) scores showing the diencephalon (<strong>a</strong>), cerebellum (<strong>b</strong>), telencephalon (<strong>c</strong>), medulla oblongata (<strong>d</strong>) and mesencephalon (<strong>e</strong>) shape distribution of snakes (coloured squares) and lizards (coloured circles) with different locomotor modes (see colour code in bottom right corner). Numbers in brackets indicate the percentage of variance explained by each of the PC axes, and 68% confidence ellipses are shown for each locomotor mode. 2D wireframes illustrate shape changes associated with the first two PCs for each brain subdivision in top and lateral (<strong>a</strong>, <strong>c</strong>, <strong>d</strong>), pial surface and lateral (<strong>b</strong>), or front and lateral (<strong>e</strong>) views.</p>
Figure 3 from "Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"
<p> </p> <p>Published as part of <a href="https://doi.org/10.1038/s41467-019-13405-w"><strong>Macrì, S <em>et al</em>., 2019, Nature Communications: 10(1):5560</strong></a></p> <p><strong>"Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"</strong> DOI: https://doi.org/10.1038/s41467-019-13405-w</p> <p> </p> <p><strong>Fig. 3</strong> <strong>Whole-brain shape variation in squamates with different locomotor behaviours.</strong> 3D plot of principal component (PC) scores showing the whole-brain shape distribution of snakes (coloured cubes) and lizards (coloured spheres) with different locomotor modes (see colour code and symbols in bottom left corner). Numbers in brackets indicate the percentage of variance explained by each of the PC axes, and 68% confidence ellipses are shown for each locomotor mode. The 3D-rendered whole-brains corresponding to extreme (indicated by coloured solid arrows, with species names) or representative (coloured dashed arrows, with species names) lizard and snake species in both positive and negative directions along the first two PCs are shown in dorsal (top) and lateral (bottom) views.</p>
Figure 2 from "Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"
<p>Published as part of <a href="https://doi.org/10.1038/s41467-019-13405-w"><strong>Macrì, S <em>et al</em>., 2019, Nature Communications: 10(1):5560</strong></a></p> <p><strong>"Comparative analysis of squamate brains unveils multi-level variation in cerebellar architecture associated with locomotor specialization"</strong> DOI: https://doi.org/10.1038/s41467-019-13405-w</p> <p> </p> <p><strong>Fig. 2<strong> </strong>Comparative anatomy of whole-brain and cerebellar cortex.</strong> <strong>a</strong> Direct comparison of dissected (top panels) and 3D reconstructed (bottom) Pogona vitticeps brain in lateral (left panels) and dorsal (right) views. <strong>b</strong>, <strong>c</strong> Single and merged immunostainings for ZIC1/2/3 granule cell marker (green) and DAPI (blue) on sagittal sections of <em>Anolis carolinensis</em> (<strong>b</strong>) and<em> Epicrates cenchria</em> (<strong>c</strong>)<strong> </strong>cerebellar cortex. White dashed lines highlight both the cerebellum profile and part of optic tectum in contact with the cerebellum to illustrate their spatial relationships in the two species. Crossed white arrows point towards rostral (R), caudal (C), dorsal (D) and ventral (V) directions. Pial and ventricular cerebellar surfaces are indicated on their respective side. GCL, granule cell layer; ML, molecular layer; IV, fourth ventricle. Scale bars: 1mm (<strong>a</strong>), 100 μm<strong> </strong>(<strong>b</strong>,<strong> </strong><strong>c</strong>).</p>
FIG. 4 in Early Miocene squamate assemblage from the Mokrá-Western Quarry (Czech Republic) and its palaeobiogeographical and palaeoenvironmental implications
FIG. 4. — Lacertoidea indet. (A, B) and? Scincoidea indet. (C, D) from the early Miocene (MN 4) of MWQ. Left dentary Pal. 1571 (2/2003 Reptile Joint) in (A) lateral and (B) medial aspects with detail of teeth. Left maxilla Pal. 1573 (2/2003 Reptile Joint) in (C) lateral and (D) medial aspects with detail of teeth. Abbreviations: dc, dental crest; cm, carina maxillaris; lf, labial foramina; Mg, Meckel`s groove; np, nasal process; sbs, subdental shelf; srs, supradental shelf; st, striations. Scale bars: A-D, 1 mm; B', D', 100 µm.
Data from: Novel approaches for phylogenetic inference from morphological data and total-evidence dating in squamate reptiles (lizards, snakes, and amphisbaenians)
Here, I combine previously underutilized models and priors to perform more biologically-realistic phylogenetic inference from morphological data, with an example from squamate reptiles. When coding morphological characters, it is often possible to denote ordered states with explicit reference to observed or hypothetical ancestral conditions. Using this logic, we can integrate across character-state labels and estimate meaningful rates of forward and backwards transitions from plesiomorphy to apomorphy. I refer to this approach as MkA, for 'asymmetric.' The MkA model incorporates the biological reality of limited reversal for many phylogenetically informative characters, and significantly increases likelihoods in the empirical datasets. Despite this, the phylogeny of Squamata remains contentious. Total-evidence analyses using combined morphological and molecular data and the MkA approach tend towards recent consensus estimates supporting a nested Iguania. However, support for this topology is not unambiguous across datasets or analyses, and no mechanism has been proposed to explain the widespread incongruence between partitions, or the hidden support for various topologies in those partitions. Furthermore, different morphological datasets produced by different authors contain both different characters and different states for the same or similar characters, resulting in drastically different placements for many important fossil lineages. Effort is needed to standardize ontology for morphology, resolve incongruence, and estimate a robust phylogeny. The MkA approach provides a preliminary avenue for investigating morphological evolution while accounting for temporal evidence and asymmetry in character-state changes.
Data from: The evolutionary economics of embryonic-sac fluids in squamate reptiles
The parchment-shelled eggs of squamate reptiles take up substantial water from the nest environment, enabling the conversion of yolk into neonatal tissue and buffering the embryo against the possibility of subsequent dry weather. During development, increasing amounts of water are stored in the embryonic sacs (i.e., membranes around the embryo: amnion, allantois, and chorion). The evolution of viviparity (prolonged uterine retention of developing embryos) means that embryonic-sac fluid storage now imposes a cost (increased maternal burdening), confers less benefit (because the mother buffers fetal water balance), and introduces a potential conflict among uterine siblings (for access to finite water supplies). Our data on nine species of squamate reptiles and published information on three species show that the embryonic-sac fluids comprise around 33% of neonatal mass in viviparous species versus 94% in full-term eggs of oviparous squamates. Data on parturition in 149 vipers (Vipera aspis, a viviparous species) show that larger offspring store more fluids in their fetal sacs and that an increase in litter size is associated with a decrease in fluid-sac mass per offspring. Overall, the evolutionary transition from oviparity to viviparity may have substantially altered selective forces on offspring packaging and created competition among offspring for access to water reserves during embryonic development.
Data from: Uterine gene expression in the live-bearing lizard, Chalcides ocellatus, reveals convergence of squamate reptile and mammalian pregnancy mechanisms
Although the morphological and physiological changes involved in pregnancy in live-bearing reptiles are well studied, the genetic mechanisms that underlie these changes are not known. We used the viviparous African Ocellated Skink, Chalcides ocellatus, as a model to identify a near complete gene expression profile associated with pregnancy using RNA-Seq analyses of uterine transcriptomes. Pregnancy in C. ocellatus is associated with upregulation of uterine genes involved with metabolism, cell proliferation and death, and cellular transport. Moreover, there are clear parallels between the genetic processes associated with pregnancy in mammals and Chalcides in expression of genes related to tissue remodeling, angiogenesis, immune system regulation, and nutrient provisioning to the embryo. In particular, the pregnant uterine transcriptome is dominated by expression of proteolytic enzymes that we speculate are involved both with remodeling the chorioallantoic placenta and histotrophy in the omphaloplacenta. Elements of the maternal innate immune system are downregulated in the pregnant uterus, indicating a potential mechanism to avoid rejection of the embryo. We found a downregulation of major histocompatability complex loci and estrogen and progesterone receptors in the pregnant uterus. This pattern is similar to mammals but cannot be explained by the mammalian model. The latter finding provides evidence that pregnancy is controlled by different endocrinological mechanisms in mammals and reptiles. Finally, 88% of the identified genes are expressed in both the pregnant and the nonpregnant uterus, and thus, morphological and physiological changes associated with C. ocellatus pregnancy are likely a result of regulation of genes continually expressed in the uterus rather than the initiation of expression of unique genes.
Data from: Integrated analyses resolve conflicts over squamate reptile phylogeny and reveal unexpected placements for fossil taxa
Squamate reptiles (lizards and snakes) are a pivotal group whose relationships have become increasingly controversial. Squamates include >9000 species, making them the second largest group of terrestrial vertebrates. They are important medicinally and as model systems for ecological and evolutionary research. However, studies of squamate biology are hindered by uncertainty over their relationships, and some consider squamate phylogeny unresolved, given recent conflicts between molecular and morphological results. To resolve these conflicts, we expand existing morphological and molecular datasets for squamates (691 morphological characters and 46 genes, for 161 living and 49 fossil taxa, including a new set of 81 morphological characters and adding two genes from published studies) and perform integrated analyses. Our results resolve higher-level relationships as indicated by molecular analyses, and reveal hidden morphological support for the molecular hypothesis (but not vice-versa). Furthermore, we find that integrating molecular, morphological, and paleontological data leads to surprising placements for two major fossil clades (Mosasauria and Polyglyphanodontia). These results further demonstrate the importance of combining fossil and molecular information, and the potential problems of estimating the placement of fossil taxa from morphological data alone. Thus, our results caution against estimating fossil relationships without considering relevant molecular data, and against placing fossils into molecular trees (e.g. for dating analyses) without considering the possible impact of molecular data on their placement.
Data from: Vertebral evolution and the diversification of squamate reptiles
Taxonomic, morphological and functional diversity are often discordant and independent components of diversity. A fundamental and largely unanswered question in evolutionary biology is why some clades diversify primarily in some of these components and not others. Dramatic variation in trunk vertebral numbers (14 to >300) among squamate reptiles coincides with different body shapes, and snake-like body shapes have evolved numerous times. However, whether increased evolutionary rates or numbers of vertebrae underlie body shape and taxonomic diversification is unknown. Using a supertree of squamates including 1375 species, and corresponding vertebral and body shape data, we show that increased rates of evolution in vertebral numbers have coincided with increased rates and disparity in body shape evolution, but not changes in rates of taxonomic diversification. We also show that the evolution of many vertebrae has not spurred or inhibited body shape or taxonomic diversification, suggesting that increased vertebral number is not a key innovation. Our findings demonstrate that lineage attributes such as the relaxation of constraints on vertebral number can facilitate the evolution of novel body shapes, but that different factors are responsible for body shape and taxonomic diversification.
Data from: Vascular patterns in iguanas and other squamates: blood vessels and sites of thermal exchange
Squamates use the circulatory system to regulate body and head temperatures during both heating and cooling. The flexibility of this system, which possibly exceeds that of endotherms, offers a number of physiological mechanisms to gain or retain heat (e.g., increase peripheral blood flow and heart rate, cooling the head to prolong basking time for the body) as well as to shed heat (modulate peripheral blood flow, expose sites of thermal exchange). Squamates also have the ability to establish and maintain the same head-to-body temperature differential that birds, crocodilians, and mammals demonstrate, but without a discrete rete or other vascular physiological device. Squamates offer important anatomical and phylogenetic evidence for the inference of the blood vessels of dinosaurs and other extinct archosaurs in that they shed light on the basal diapsid condition. Given this basal positioning, squamates likewise inform and constrain the range of physiological thermoregulatory mechanisms that may have been found in Dinosauria. Unfortunately, the literature on squamate vascular anatomy is limited. Cephalic vascular anatomy of green iguanas (Iguana iguana) was investigated using a differential-contrast, dual-vascular injection (DCDVI) technique and high-resolution X-ray microcomputed tomography (μCT). Blood vessels were digitally segmented to create a surface representation of vascular pathways. Known sites of thermal exchange, consisting of the oral, nasal, and orbital regions, were given special attention due to their role in brain and cephalic thermoregulation. Blood vessels to and from sites of thermal exchange were investigated to detect conserved vascular patterns and to assess their ability to deliver cooled blood to the dural venous sinuses. Arteries within sites of thermal exchange were found to deliver blood directly and through collateral pathways. The venous drainage was found to have multiple pathways that could influence neurosensory tissue temperature, as well as pathways that would bypass neurosensory tissues. The orbital region houses a large venous sinus that receives cooled blood from the nasal region. Blood vessels from the nasal region and orbital sinus show anastomotic connections to the dural sinus system, allowing for the direct modulation of brain temperatures. The generality of the vascular patterns discovered in iguanas were assessed by firsthand comparison with other squamates taxa (e.g., via dissection and osteological study) as well as the literature. Similar to extant archosaurs, iguanas and other squamates have highly vascularized sites of thermal exchange that likely support physiological thermoregulation that "fine tunes" temperatures attained through behavioral thermoregulation.
FIGURE 5. Anterior squamation, A. Sarotherodon knauerae, B in Two new sympatric Sarotherodon species (Pisces: Cichlidae) endemic to Lake Ejagham, Cameroon, west-central Africa, with comments on the Sarotherodon galilaeus species complex
FIGURE 5. Anterior squamation, A. Sarotherodon knauerae, B. Sarotherodon lamprechti.
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