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International Review of Cell and... 2009The amphibian gastrula can be regarded as a single coherent tissue which folds and distorts itself in a reproducible pattern to establish the embryonic germ layers. It... (Review)
Review
The amphibian gastrula can be regarded as a single coherent tissue which folds and distorts itself in a reproducible pattern to establish the embryonic germ layers. It is held together by cadherins which provide the flexible adhesion required for the massive cell rearrangements that accompany gastrulation. Cadherin expression and adhesiveness increase as one goes from the vegetal cell mass through the anterior mesendoderm to the chordamesoderm, and then decrease again slightly in the ectoderm. Together with a basic random component of cell motility, this flexible, differentially expressed adhesiveness generates surface and interfacial tension effects which, in principle, can exert strong forces. However, conclusive evidence for an in vivo role of differential adhesion-related effects in gastrula morphogenesis is still lacking. The most important morphogenetic process in the amphibian gastrula seems to be intercellular migration, where cells crawl actively across each other's surface. The crucial aspect of this process is that cell motility is globally oriented, leading for example to mediolateral intercalation of bipolar cells during convergent extension of the chordamesoderm or to the directional migration of unipolar cells during translocation of the anterior mesendoderm on the ectodermal blastocoel roof. During these movements, the boundary between ectoderm and mesoderm is maintained by a tissue separation process.
Topics: Amphibians; Animals; Cell Adhesion; Gastrulation
PubMed: 19815180
DOI: 10.1016/S1937-6448(09)78005-0 -
Proceedings. Biological Sciences Feb 2019The exponential increase in species introductions during the Anthropocene has brought about a major loss of biodiversity. Amphibians have suffered large declines, with... (Meta-Analysis)
Meta-Analysis
The exponential increase in species introductions during the Anthropocene has brought about a major loss of biodiversity. Amphibians have suffered large declines, with more than 16% considered to be threatened by invasive species. We conducted a global meta-analysis of the impacts of alien species on native amphibians to determine which aspects of amphibian ecology are most affected by plant, invertebrate, fish, amphibian, reptile, or mammal introductions. Measures of fitness were most strongly affected; amphibian performance was consistently lower in the presence of alien species. While exposure to alien species caused a significant decrease in amphibian behavioural activity when compared with a no species control, this response was stronger towards a control of native impacting species. This indicates a high degree of prey naiveté towards alien species and highlights the importance of using different types of controls in empirical studies. Alien invertebrates had the greatest overall impact on amphibians. This study sets a new agenda for research on biological invasions, highlighting the lack of studies investigating the impacts of alien species on amphibian terrestrial life-history stages. It also emphasizes the strong ecological impacts that alien species have on amphibian fitness and suggests that future introductions or global spread of alien invertebrates could strongly exacerbate current amphibian declines.
Topics: Amphibians; Animal Distribution; Animals; Genetic Fitness; Introduced Species; Invertebrates; Plants; Population Dynamics; Vertebrates
PubMed: 30963838
DOI: 10.1098/rspb.2018.2528 -
PloS One 2017Skin as the first barrier against external invasions plays an essential role for the survival of amphibians on land. Understanding the genetic basis of skin function is... (Comparative Study)
Comparative Study
Skin as the first barrier against external invasions plays an essential role for the survival of amphibians on land. Understanding the genetic basis of skin function is significant in revealing the mechanisms underlying immunity of amphibians. In this study, we de novo sequenced and comparatively analyzed skin transcriptomes from three different amphibian species, Andrias davidianus, Bufo gargarizans, and Rana nigromaculata Hallowell. Functional classification of unigenes in each amphibian showed high accordance, with the most represented GO terms and KEGG pathways related to basic biological processes, such as binding and metabolism and immune system. As for the unigenes, GO and KEGG distributions of conserved orthologs in each species were similar, with the predominantly enriched pathways including RNA polymerase, nucleotide metabolism, and defense. The positively selected orthologs in each amphibian were also similar, which were primarily involved in stimulus response, cell metabolic, membrane, and catalytic activity. Furthermore, a total of 50 antimicrobial peptides from 26 different categories were identified in the three amphibians, and one of these showed high efficiency in inhibiting the growth of different bacteria. Our understanding of innate immune function of amphibian skin has increased basis on the immune-related unigenes, pathways, and antimicrobial peptides in amphibians.
Topics: Amphibians; Animals; Skin; Transcriptome
PubMed: 29267366
DOI: 10.1371/journal.pone.0190023 -
Developmental Biology (New York, N.Y. :... 1986
Review
Topics: Amphibians; Animals; Cell Differentiation; Gastrula; Morphogenesis
PubMed: 3078116
DOI: 10.1007/978-1-4613-2141-5_7 -
Annual Review of Microbiology Oct 2021Ancient enzootic associations between wildlife and their infections allow evolution to innovate mechanisms of pathogenicity that are counterbalanced by host responses.... (Review)
Review
Ancient enzootic associations between wildlife and their infections allow evolution to innovate mechanisms of pathogenicity that are counterbalanced by host responses. However, erosion of barriers to pathogen dispersal by globalization leads to the infection of hosts that have not evolved effective resistance and the emergence of highly virulent infections. Global amphibian declines driven by the rise of chytrid fungi and chytridiomycosis are emblematic of emerging infections. Here, we review how modern biological methods have been used to understand the adaptations and counteradaptations that these fungi and their amphibian hosts have evolved. We explore the interplay of biotic and abiotic factors that modify the virulence of these infections and dissect the complexity of this disease system. We highlight progress that has led to insights into how we might in the future lessen the impact of these emerging infections.
Topics: Amphibians; Animals; Chytridiomycota; Mycoses; Virulence
PubMed: 34351790
DOI: 10.1146/annurev-micro-052621-124212 -
Genesis (New York, N.Y. : 2000) Mar 2012Amphibians including the South African clawed frog Xenopus laevis, its close relative Xenopus tropicalis, and the Mexican axolotl (Ambystoma mexicanum) are important... (Review)
Review
Amphibians including the South African clawed frog Xenopus laevis, its close relative Xenopus tropicalis, and the Mexican axolotl (Ambystoma mexicanum) are important vertebrate models for cell biology, development, and regeneration. For the analysis of embryos and larva with altered gene expression in gain-of-function or loss-of-function studies histology is increasingly important. Here, we discuss plastic or resin embedding of embryos as valuable alternatives to conventional paraffin embedding. For example, microwave-assisted tissue processing, combined with embedding in the glycol methacrylate Technovit 7100, is a fast, simple, and reliable method to obtain state-of-the-art histology with high resolution of cellular details in less than a day. Microwave-processed samples embedded in Epon 812 are also useful for transmission electron microscopy. Finally, Technovit-embedded samples are well suited for serial section analysis of embryos labeled either by whole-mount immunofluorescence, or with tracers such as GFP or fluorescent dextrans. Therefore, plastic embedding offers a versatile alternative to paraffin embedding for routine histology and immunocytochemistry of amphibian embryos.
Topics: Amphibians; Animals; Embryo, Nonmammalian; Histological Techniques; Larva; Paraffin Embedding; Plastic Embedding
PubMed: 22083609
DOI: 10.1002/dvg.20821 -
The Veterinary Clinics of North... Jan 2021Amphibians represent a diverse group of animals with highly varied behaviors depending on their anatomy, physiology, and ecological niche. Behavioral and welfare issues... (Review)
Review
Amphibians represent a diverse group of animals with highly varied behaviors depending on their anatomy, physiology, and ecological niche. Behavioral and welfare issues in amphibians are frequent in captive settings and warrant evaluation. Welfare criteria and clinical diagnostic assays when combined with a comprehension of the natural history of a species are useful tools to improve both the well-being of the individual animal and the population. Correction of environmental factors that affect behavior and, secondarily, survival and reproduction is important in captivity and for the conservation of wild populations.
Topics: Amphibians; Animal Husbandry; Animal Welfare; Animals; Behavior, Animal; Pets
PubMed: 33189251
DOI: 10.1016/j.cvex.2020.09.009 -
The Science of the Total Environment Apr 2013The input of agrochemicals has contributed to alteration of community composition in managed and associated natural systems, including amphibian biodiversity. Pesticides... (Meta-Analysis)
Meta-Analysis
The input of agrochemicals has contributed to alteration of community composition in managed and associated natural systems, including amphibian biodiversity. Pesticides and fertilizers negatively affect many amphibian species and can cause mortality and sublethal effects, such as reduced growth and increased susceptibility to disease. However, the effect of pesticides and fertilizers varies among amphibian species. We used meta-analytic techniques to quantify the lethal and sublethal effects of pesticides and fertilizers on amphibians in an effort to review the published work to date and produce generalized conclusions. We found that pesticides and fertilizers had a negative effect on survival of -0.9027 and growth of -0.0737 across all reported amphibian species. We also observed differences between chemical classes in their impact on amphibians: inorganic fertilizers, organophosphates, chloropyridinyl, phosphonoglycines, carbamates, and triazines negatively affected amphibian survival, while organophosphates and phosphonoglycines negatively affected amphibian growth. Our results suggest that pesticides and fertilizers are an important stressor for amphibians in agriculturally dominated systems. Furthermore, certain chemical classes are more likely to harm amphibians. Best management practices in agroecosystems should incorporate amphibian species-specific response to agrochemicals as well as life stage dependent susceptibility to best conserve amphibian biodiversity in these landscapes.
Topics: Amphibians; Animals; Fertilizers; Models, Theoretical; Pesticides; Survival Analysis
PubMed: 23422494
DOI: 10.1016/j.scitotenv.2013.01.056 -
Proceedings of the National Academy of... Apr 1971Amphibian haploid genome sizes vary from 9 x 10(8) to 8 x 10(10) nucleotide pairs. The rate of reassociation of DNA from amphibians of different genome sizes has been...
Amphibian haploid genome sizes vary from 9 x 10(8) to 8 x 10(10) nucleotide pairs. The rate of reassociation of DNA from amphibians of different genome sizes has been employed to eliminate one of the theoretical models of chromosome structure. Scaphiopus couchi, Bufo marinus, and Rana clamitans, whose haploid genome sizes are in the ratio 2:7:10, all contain sequences of DNA represented once in the haploid genome. This indicates that their chromosomes are not composed of identical lateral strands (polynemy). The relative frequencies of repetition of DNA sequences are different for the various species of amphibians. The observed frequencies of repetitive DNA sequences in amphibians do not show the relationships expected if amphibians form a polyneme series.
Topics: Amphibians; Animals; Anura; Chemical Phenomena; Chemistry; Chromosomes; Cytogenetics; DNA; Genetic Code; In Vitro Techniques; Kinetics; Models, Structural; Nucleotides; Species Specificity; Urodela
PubMed: 5279521
DOI: 10.1073/pnas.68.4.799 -
Diseases of Aquatic Organisms Jul 2018The ability to isolate and purify pathogens is important for the study of infectious disease. A protocol for isolating Batrachochytrium dendrobatidis (Bd), a lethal...
The ability to isolate and purify pathogens is important for the study of infectious disease. A protocol for isolating Batrachochytrium dendrobatidis (Bd), a lethal pathogen of amphibians, has been available for over a decade, but the method relies on sacrificing infected animals. We validated a non-lethal protocol for Bd isolation that uses biopsy punches from toe webbing to collect skin samples from live amphibians in remote field locations. We successfully isolated Bd from the Cascades frog Rana cascadae and found a positive association between Bd infection and probability of Bd growth in culture. Recapture rates of sampled animals suggest that our isolation protocol did not affect frog survival. The ability to collect isolates from live animals will facilitate investigations of the biology of Bd and enhance amphibian conservation efforts.
Topics: Amphibians; Animals; Chytridiomycota; Mycoses
PubMed: 29972376
DOI: 10.3354/dao03238