Evolutionary Insights into the Relationship of Frogs, Salamanders, and Caecilians and Their Adaptive Traits, with an Emphasis on Salamander Regeneration and Longevity
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PROVIDER: S-EPMC10668855 | biostudies-literature | 2023 Nov
REPOSITORIES: biostudies-literature
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Project description:Appendage regeneration is one of the most compelling phenomena in regenerative biology and is extensively studied in axolotls and newts. However, the regenerative capacity in other families of salamanders remains poorly described. Here we characterize the limb regeneration process in Bolitoglossa ramosi, a direct-developing terrestrial salamander of the plethodontid family. We (1) describe the major morphological features at different stages of limb regeneration, (2) show that appendage regeneration in a terrestrial salamander varies from other amphibians and (3) show that limb regeneration in this species is considerably slower than in axolotls and newts (95 days post-amputation for complete regeneration) despite having a significantly smaller genome size than axolotls or newts.
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Project description:The origin of extant amphibians remains largely obscure, with only a few early Mesozoic stem taxa known, as opposed to a much better fossil record from the mid-Jurassic on. In recent time, anurans have been traced back to Early Triassic forms and caecilians have been traced back to the Late Jurassic Eocaecilia, both of which exemplify the stepwise acquisition of apomorphies. Yet the most ancient stem-salamanders, known from mid-Jurassic rocks, shed little light on the origin of the clade. The gap between salamanders and other lissamphibians, as well as Paleozoic tetrapods, remains considerable. Here we report a new specimen of Triassurus sixtelae, a hitherto enigmatic tetrapod from the Middle/Late Triassic of Kyrgyzstan, which we identify as the geologically oldest stem-group salamander. This sheds light not only on the early evolution of the salamander body plan, but also on the origin of the group as a whole. The new, second specimen is derived from the same beds as the holotype, the Madygen Formation of southwestern Kyrgyzstan. It reveals a range of salamander characters in this taxon, pushing back the rock record of urodeles by at least 60 to 74 Ma (Carnian-Bathonian). In addition, this stem-salamander shares plesiomorphic characters with temnospondyls, especially branchiosaurids and amphibamiforms.
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Project description:In frogs and salamanders, movements of the eyeballs in association with an open palate have often been proposed to play a functional role in lung breathing. In this "palatal buccal pump," the eyeballs are elevated during the lowering of the buccal floor to suck air in through the nares, and the eyeballs are lowered during elevation of the buccal floor to help press air into the lungs. Here, we used X-Ray Reconstruction of Moving Morphology to investigate eye movements during lung breathing and feeding in bullfrogs and axolotls. Our data do not show eye movements that would be in accordance with the palatal buccal pump. On the contrary, there is a small passive elevation of the eyeballs when the buccal floor is raised. Inward drawing of the eyeballs occurs only during body motion and for prey transport in bullfrogs, but this was not observed in axolotls. Each eye movement in bullfrogs has a vertical, a mediolateral, and an anteroposterior component. Considering the surprisingly weak posterior motion component of the eyeballs, their main role in prey transport might be fixing the prey by pressing it against the buccal floor. The retraction of the buccal floor would then contribute to the posterior push of the prey. Because our study provides no evidence for a palatal buccal pump in frogs and salamanders, there is also no experimental support for the idea of a palatal buccal pump in extinct temnospondyl amphibians, in contrast to earlier suggestions.
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Project description:BACKGROUND: Cyanobacteria belong to an ancient group of photosynthetic prokaryotes with pronounced variations in their cellular differentiation strategies, physiological capacities and choice of habitat. Sequencing efforts have shown that genomes within this phylum are equally diverse in terms of size and protein-coding capacity. To increase our understanding of genomic changes in the lineage, the genomes of 58 contemporary cyanobacteria were analysed for shared and unique orthologs. RESULTS: A total of 404 protein families, present in all cyanobacterial genomes, were identified. Two of these are unique to the phylum, corresponding to an AbrB family transcriptional regulator and a gene that escapes functional annotation although its genomic neighbourhood is conserved among the organisms examined. The evolution of cyanobacterial genome sizes involves a mix of gains and losses in the clade encompassing complex cyanobacteria, while a single event of reduction is evident in a clade dominated by unicellular cyanobacteria. Genome sizes and gene family copy numbers evolve at a higher rate in the former clade, and multi-copy genes were predominant in large genomes. Orthologs unique to cyanobacteria exhibiting specific characteristics, such as filament formation, heterocyst differentiation, diazotrophy and symbiotic competence, were also identified. An ancestral character reconstruction suggests that the most recent common ancestor of cyanobacteria had a genome size of approx. 4.5 Mbp and 1678 to 3291 protein-coding genes, 4%-6% of which are unique to cyanobacteria today. CONCLUSIONS: The different rates of genome-size evolution and multi-copy gene abundance suggest two routes of genome development in the history of cyanobacteria. The expansion strategy is driven by gene-family enlargment and generates a broad adaptive potential; while the genome streamlining strategy imposes adaptations to highly specific niches, also reflected in their different functional capacities. A few genomes display extreme proliferation of non-coding nucleotides which is likely to be the result of initial expansion of genomes/gene copy number to gain adaptive potential, followed by a shift to a life-style in a highly specific niche (e.g. symbiosis). This transition results in redundancy of genes and gene families, leading to an increase in junk DNA and eventually to gene loss. A few orthologs can be correlated with specific phenotypes in cyanobacteria, such as filament formation and symbiotic competence; these constitute exciting exploratory targets.
| S-EPMC3141437 | biostudies-literature
Project description:Caecilians (order Gymnophiona) are apodan, snake-like amphibians, usually with fossorial habits, constituting one of the most unknown groups of terrestrial vertebrates. As in orders Anura (frogs, tree frogs and toads) and Caudata (salamanders and newts), the caecilian skin is rich in mucous glands, responsible for body lubrication, and poison glands, producing varied toxins used in defence against predators and microorganisms. Whereas in anurans and caudatans skin gland morphology has been well studied, caecilian poison glands remain poorly elucidated. Here we characterised the skin gland morphology of the caecilian Siphonops annulatus, emphasising the poison glands in comparison to those of anurans and salamanders. We showed that S. annulatus glands are similar to those of salamanders, consisting of several syncytial compartments full of granules composed of protein material but showing some differentiated apical compartments containing mucus. An unusual structure resembling a mucous gland is frequently observed in lateral/apical position, apparently connected to the main duct. We conclude that the morphology of skin poison glands in caecilians is more similar to salamander glands when compared to anuran glands that show a much-simplified structure.
| S-EPMC8617868 | biostudies-literature
Project description:Recent studies have reported that independent adaptive radiations can lead to identical ecomorphs. Our phylogenetic analyses of nuclear and mitochondrial DNA sequences here indicate that a major radiation of ranid frogs on Madagascar produced morphological, physiological, and developmental characters that are remarkably similar to those that independently evolved on the Indian subcontinent. We demonstrate further that, in several cases, adult and larval stages each evolved sets of characters which are not only convergent between independent lineages, but also allowed both developmental stages to invade the same adaptive zone. It is likely that such covariations are produced by similar selective pressures on independent larval and adult characters rather than by genetic or functional linkage. We briefly discuss why larval/adult covariations might constitute an important evolutionary phenomenon in species for which more than one developmental stage potentially has access to multiple environmental conditions.
| S-EPMC18667 | biostudies-literature
Project description:Mercury (Hg) has accumulated in forested landscapes in the Northeastern U.S., and hotspots with enhanced deposition have been identified throughout the region. Due to a variety of favorable landscape characteristics, including relatively high dissolved organic carbon (DOC), fluctuating water levels, and low pH and dissolved oxygen, vernal pools provide ideal conditions for the conversion of Hg to its more toxic and bioavailable form, methylmercury (MeHg). Yet little is known about the concentrations, speciation, and bioavailability of Hg in vernal pools, or its bioaccumulation in vernal pool fauna and potential export into terrestrial systems. We investigated the role of forest cover type on the bioaccumulation of MeHg in wood frog (Lithobates sylvatica) and spotted salamander (Ambystoma maculatum) eggs, larvae, and adults, and investigated relationships among MeHg and water chemistry (pH, DOC). Water samples from pools located in coniferous stands had greater concentrations of THg and MeHg compared to deciduous pool water, and showed significant positive correlation to DOC (r?=?0.683, P?<?0.001) and correlated negatively with pH (r?=?-0.613, P?<?0.001). Methylmercury levels in amphibian embryos were similar between the two species (L. sylvatica mean?=?5.4?ng/g dw; A. maculatum mean?=?3.5?ng/g dw). Concentrations of MeHg increased substantially in larvae, and were significantly greater in A. maculatum (mean?=?237.6?ng/g?±?18.5 SE) than L. sylvatica larvae (62.5?ng/g?±?5.7 SE). Forest cover type did not explain variation in MeHg concentration among amphibian embryos or larvae. Methylmercury levels in adult tissue samples were significantly greater in A. maculatum (mean?=?79.9?ng/g?±?8.9 SE) compared to L. sylvatica (mean?=?47.7?ng/g?±?9.7 SE). This research demonstrates that vernal pools are important hotspots where amphibians bioaccumulate MeHg, which may then be transferred to terrestrial ecosystems. The abundance of amphibian larvae suggests they could be important bioindicators for monitoring MeHg loading and bioavailability.
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Project description:Salamanders are unique among tetrapods in their ability to regenerate their limbs throughout life. Like other poikilothermic amphibians, salamanders also show a remarkable capacity to survive long periods of starvation. Whether the physiological reserves necessary for tissue regeneration are preserved or sacrificed in starved salamanders is unknown. In the current study, we maintained Iberian ribbed newts ( Pleurodeles waltl) under extreme physiological stress to assess the extent of regeneration and identify the molecular and cellular changes that may occur under such conditions. After 19 months of complete food deprivation, the animals exhibited extensive morphological and physiological adaptations but remained behaviorally active and vigilant. Autophagy was elevated in different tissues and the transformed gut microbiota indicated remodeling of the intestinal tract related to autophagy. Upon limb amputation in animals starved for 21 months, regeneration proceeded with progenitor cell proliferation and migration, leading to limb blastema formation. However, limb outgrowth and patterning were substantially attenuated. Blockage of autophagy inhibited cell proliferation and blastema formation in starved animals, but not in fed animals. Hence, tissue autophagy and the regenerative response were tightly coupled only when animals were under stress. Our results demonstrate that under adverse conditions, salamanders can exploit alternative strategies to secure blastema formation for limb regeneration.
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Project description:The failure to replace damaged body parts in adult mammals results from a muted growth response and fibrotic scarring. Although infiltrating immune cells play a major role in determining the variable outcome of mammalian wound repair, little is known about the modulation of immune cell signaling in efficiently regenerating species such as the salamander, which can regrow complete body structures as adults. Here we present a comprehensive analysis of immune signaling during limb regeneration in axolotl, an aquatic salamander, and reveal a temporally defined requirement for macrophage infiltration in the regenerative process. Although many features of mammalian cytokine/chemokine signaling are retained in the axolotl, they are more dynamically deployed, with simultaneous induction of inflammatory and anti-inflammatory markers within the first 24 h after limb amputation. Systemic macrophage depletion during this period resulted in wound closure but permanent failure of limb regeneration, associated with extensive fibrosis and disregulation of extracellular matrix component gene expression. Full limb regenerative capacity of failed stumps was restored by reamputation once endogenous macrophage populations had been replenished. Promotion of a regeneration-permissive environment by identification of macrophage-derived therapeutic molecules may therefore aid in the regeneration of damaged body parts in adult mammals.
| S-EPMC3677454 | biostudies-literature
Project description:One or more members of four living amphibian clades have independently dispensed with pulmonary respiration and lack lungs, but little is known of the developmental basis of lung loss in any taxon. We use morphological, molecular, and experimental approaches to examine the Plethodontidae, a dominant family of salamanders, all of which are lungless as adults. We confirm an early anecdotal report that plethodontids complete early stages of lung morphogenesis: Transient embryonic lung primordia form but regress by apoptosis before hatching. Initiation of pulmonary development coincides with expression of the lung-specification gene Wnt2b in adjacent mesoderm, and the lung rudiment expresses pulmonary markers Nkx2.1 and Sox9. Lung developmental-genetic pathways are at least partially conserved despite the absence of functional adult lungs for at least 25 and possibly exceeding 60 million years. Adult lung loss appears associated with altered expression of signaling molecules that mediate later stages of tracheal and pulmonary development.
| S-EPMC9385146 | biostudies-literature