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Current Biology : CB Nov 2018Since the dawn of history, amphibians have been a part of human culture. Western Europeans built fires for cooking and warmth, adding large logs as needed. What...
Since the dawn of history, amphibians have been a part of human culture. Western Europeans built fires for cooking and warmth, adding large logs as needed. What occasionally emerged was astounding: large black animals (which had found shelter in the logs) with four legs and a tail, jet black with striking bright yellow spots. These fire salamanders were variously thought to be the product of the fire itself, or, as Aristotle reported, capable of extinguishing fire. Pliny the Elder is said to have tested this idea by throwing a salamander into flames - the salamander died! - nevertheless the association with fire persisted. Pliny perpetuated other fantastical claims, which spread; even Leonardo da Vinci contributed to the legend, and myths from different regions merged - at one point, asbestos was claimed to be salamander wool. Salamanders were attributed great powers; a single salamander upstream was thought to be sufficient to kill an army. King Francis I. of France chose a salamander as his emblem - a powerful symbol, born of fire, filled with poison, immune from burning, and even able to douse flames. Before the emergence of great cities and conurbations, people grew up surrounded by nature. Salamanders and newts, toads and frogs were all part of normal human experience. Myths such as those surrounding the fire salamanders were commonplace. Shakespeare's witches brewed with an eye of newt and tail of frog. As a child, we raised tadpoles and were taught to shudder at the appearance of a tiger salamander in a root cellar. In general, amphibians are seen as benign and harmless, even helpful as creatures that devour harmful insects and serve as an alternative food source. Thus, it came as a shock to most biologists and to the public at large in the 1980s that amphibians around the world were in decline and that they were at greater risk of extinction as a taxon than any other vertebrate group. A study of every amphibian species known in 2004 showed that on the order of 40% were at high risk of extinction, and by 2008, the decline of amphibians was seen as evidence of an impending sixth mass extinction.
Topics: Amphibians; Animal Distribution; Animals; Biodiversity; Chytridiomycota; Conservation of Natural Resources; Life History Traits; Mycoses
PubMed: 30399342
DOI: 10.1016/j.cub.2018.09.028 -
Current Biology : CB Jan 2023Vanessa Smilansky and Thomas A. Richards introduce Perkinsea - a lineage of freshwater parasitic protists that infect certain amphibians and cause of severe Perkinsea...
Vanessa Smilansky and Thomas A. Richards introduce Perkinsea - a lineage of freshwater parasitic protists that infect certain amphibians and cause of severe Perkinsea infection.
Topics: Animals; Alveolata; Amphibians; Fresh Water
PubMed: 36626865
DOI: 10.1016/j.cub.2022.11.032 -
Sexual Development : Genetics,... 2016Amphibians have been widely used to study developmental biology due to the fact that embryo development takes place independently of the maternal organism and that... (Review)
Review
Amphibians have been widely used to study developmental biology due to the fact that embryo development takes place independently of the maternal organism and that observations and experimental approaches are easy. Some amphibians like Xenopus became model organisms in this field. In the first part of this article, the differentiation of the gonads in amphibians and the mechanisms governing this process are reviewed. In the second part, the state of the art about sex reversal, which can be induced by steroid hormones in general and by temperature in some species, is presented. Also information about pollutants found in the environment that could interfere with the development of the amphibian reproductive apparatus or with their reproductive physiology is given. Such compounds could play a part in the amphibian decline, since in the wild, many amphibians are endangered species.
Topics: Amphibians; Animals; Disorders of Sex Development; Gonads; Reproduction; Sex Differentiation
PubMed: 27648840
DOI: 10.1159/000448797 -
Parasites & Vectors Jun 2021Parasites, including viruses, bacteria, fungi, protists, helminths, and arthropods, are ubiquitous in the animal kingdom. Consequently, hosts are frequently infected... (Review)
Review
Parasites, including viruses, bacteria, fungi, protists, helminths, and arthropods, are ubiquitous in the animal kingdom. Consequently, hosts are frequently infected with more than one parasite species simultaneously. The assessment of such co-infections is of fundamental importance for disease ecology, but relevant studies involving non-domesticated animals have remained scarce. Many amphibians are in decline, and they generally have a highly diverse parasitic fauna. Here we review the literature reporting on field surveys, veterinary case studies, and laboratory experiments on co-infections in amphibians, and we summarize what is known about within-host interactions among parasites, which environmental and intrinsic factors influence the outcomes of these interactions, and what effects co-infections have on hosts. The available literature is piecemeal, and patterns are highly diverse, so that identifying general trends that would fit most host-multiparasite systems in amphibians is difficult. Several examples of additive, antagonistic, neutral, and synergistic effects among different parasites are known, but whether members of some higher taxa usually outcompete and override the effects of others remains unclear. The arrival order of different parasites and the time lag between exposures appear in many cases to fundamentally shape competition and disease progression. The first parasite to arrive can gain a marked reproductive advantage or induce cross-reaction immunity, but by disrupting the skin and associated defences (i.e., skin secretions, skin microbiome) and by immunosuppression, it can also pave the way for subsequent infections. Although there are exceptions, detrimental effects to the host are generally aggravated with increasing numbers of co-infecting parasite species. Finally, because amphibians are ectothermic animals, temperature appears to be the most critical environmental factor that affects co-infections, partly via its influence on amphibian immune function, partly due to its direct effect on the survival and growth of parasites. Besides their importance for our understanding of ecological patterns and processes, detailed knowledge about co-infections is also crucial for the design and implementation of effective wildlife disease management, so that studies concentrating on the identified gaps in our understanding represent rewarding research avenues.
Topics: Amphibians; Animals; Animals, Wild; Coinfection; Host-Parasite Interactions; Parasites; Parasitic Diseases, Animal
PubMed: 34082796
DOI: 10.1186/s13071-021-04796-1 -
Genes Apr 2021Sex is determined genetically in amphibians; however, little is known about the sex chromosomes, testis-determining genes, and the genes involved in testis... (Review)
Review
Sex is determined genetically in amphibians; however, little is known about the sex chromosomes, testis-determining genes, and the genes involved in testis differentiation in this class. Certain inherent characteristics of the species of this group, like the homomorphic sex chromosomes, the high diversity of the sex-determining mechanisms, or the existence of polyploids, may hinder the design of experiments when studying how the gonads can differentiate. Even so, other features, like their external development or the possibility of inducing sex reversal by external treatments, can be helpful. This review summarizes the current knowledge on amphibian sex determination, gonadal development, and testis differentiation. The analysis of this information, compared with the information available for other vertebrate groups, allows us to identify the evolutionarily conserved and divergent pathways involved in testis differentiation. Overall, the data confirm the previous observations in other vertebrates-the morphology of the adult testis is similar across different groups; however, the male-determining signal and the genetic networks involved in testis differentiation are not evolutionarily conserved.
Topics: Amphibians; Animals; Cell Differentiation; Male; Polyploidy; Sex Determination Processes; Testis
PubMed: 33923451
DOI: 10.3390/genes12040578 -
Genes Aug 2019In this contribution, the aspects of reptile and amphibian speciation that emerged from research performed over the past decade are reviewed. First, this study assesses... (Review)
Review
In this contribution, the aspects of reptile and amphibian speciation that emerged from research performed over the past decade are reviewed. First, this study assesses how patterns and processes of speciation depend on knowing the taxonomy of the group in question, and discuss how integrative taxonomy has contributed to speciation research in these groups. This study then reviews the research on different aspects of speciation in reptiles and amphibians, including biogeography and climatic niches, ecological speciation, the relationship between speciation rates and phenotypic traits, and genetics and genomics. Further, several case studies of speciation in reptiles and amphibians that exemplify many of these themes are discussed. These include studies of integrative taxonomy and biogeography in South American lizards, ecological speciation in European salamanders, speciation and phenotypic evolution in frogs and lizards. The final case study combines genomics and biogeography in tortoises. The field of amphibian and reptile speciation research has steadily moved forward from the assessment of geographic and ecological aspects, to incorporating other dimensions of speciation, such as genetic mechanisms and evolutionary forces. A higher degree of integration among all these dimensions emerges as a goal for future research.
Topics: Amphibians; Animals; Ecosystem; Evolution, Molecular; Genetic Speciation; Reptiles; Selection, Genetic
PubMed: 31455040
DOI: 10.3390/genes10090646 -
Philosophical Transactions of the Royal... Jul 2023Animal defences against infection involve two distinct but complementary mechanisms: tolerance and resistance. Tolerance measures the animal's ability to limit... (Review)
Review
Animal defences against infection involve two distinct but complementary mechanisms: tolerance and resistance. Tolerance measures the animal's ability to limit detrimental effects from a given infection, whereas resistance is the ability to limit the intensity of that infection. Tolerance is a valuable defence for highly prevalent, persistent or endemic infections where mitigation strategies based on traditional resistance mechanisms are less effective or evolutionarily stable. Selective breeding of amphibians for enhanced tolerance to spp has been suggested as a strategy for mitigating the impacts of the fungal disease, chytridiomycosis. Here, we define infection tolerance and resistance in the context of chytridiomycosis, present evidence for variation in tolerance to chytridiomycosis, and explore epidemiological, ecological and evolutionary implications of tolerance to chytridiomycosis. We found that exposure risk and environmental moderation of infection burdens are major confounders of resistance and tolerance, chytridiomycosis is primarily characterized by variation in constitutive rather than adaptive resistance, tolerance is epidemiologically important in driving pathogen spread and maintenance, heterogeneity of tolerance leads to ecological trade-offs, and natural selection for resistance and tolerance is likely to be dilute. Improving our understanding of infection tolerance broadens our capacity for mitigating the ongoing impacts of emerging infectious diseases such as chytridiomycosis. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'.
Topics: Animals; Mycoses; Amphibians; Biological Evolution; Communicable Diseases, Emerging; Immune Tolerance
PubMed: 37305912
DOI: 10.1098/rstb.2022.0133 -
Cells May 2022In multicellular organisms, development is based in part on the integration of communication systems. Two neuroendocrine axes, the hypothalamic-pituitary-thyroid and the... (Review)
Review
In multicellular organisms, development is based in part on the integration of communication systems. Two neuroendocrine axes, the hypothalamic-pituitary-thyroid and the hypothalamic-pituitary-adrenal/interrenal axes, are central players in orchestrating body morphogenesis. In all vertebrates, the hypothalamic-pituitary-thyroid axis controls thyroid hormone production and release, whereas the hypothalamic-pituitary-adrenal/interrenal axis regulates the production and release of corticosteroids. One of the most salient effects of thyroid hormones and corticosteroids in post-embryonic developmental processes is their critical role in metamorphosis in anuran amphibians. Metamorphosis involves modifications to the morphological and biochemical characteristics of all larval tissues to enable the transition from one life stage to the next life stage that coincides with an ecological niche switch. This transition in amphibians is an example of a widespread phenomenon among vertebrates, where thyroid hormones and corticosteroids coordinate a post-embryonic developmental transition. The review addresses the functions and interactions of thyroid hormone and corticosteroid signaling in amphibian development (metamorphosis) as well as the developmental roles of these two pathways in vertebrate evolution.
Topics: Adrenal Cortex Hormones; Amphibians; Animals; Metamorphosis, Biological; Thyroid Gland; Thyroid Hormones; Vertebrates
PubMed: 35626631
DOI: 10.3390/cells11101595 -
Biomolecules Nov 2014Although lymphocyte-like cells secreting somatically-recombining receptors have been identified in the jawless fishes (hagfish and lamprey), the cartilaginous fishes... (Review)
Review
Although lymphocyte-like cells secreting somatically-recombining receptors have been identified in the jawless fishes (hagfish and lamprey), the cartilaginous fishes (sharks, skates, rays and chimaera) are the most phylogenetically distant group relative to mammals in which bona fide immunoglobulins (Igs) have been found. Studies of the antibodies and humoral immune responses of cartilaginous fishes and other cold-blooded vertebrates (bony fishes, amphibians and reptiles) are not only revealing information about the emergence and roles of the different Ig heavy and light chain isotypes, but also the evolution of specialised adaptive features such as isotype switching, somatic hypermutation and affinity maturation. It is becoming increasingly apparent that while the adaptive immune response in these vertebrate lineages arose a long time ago, it is most definitely not primitive and has evolved to become complex and sophisticated. This review will summarise what is currently known about the immunoglobulins of cold-blooded vertebrates and highlight the differences, and commonalities, between these and more "conventional" mammalian species.
Topics: Adaptive Immunity; Amphibian Proteins; Amphibians; Animals; Evolution, Molecular; Fishes; Immunoglobulin Isotypes; Immunoglobulins; Phylogeny; Reptiles; Vertebrates
PubMed: 25427250
DOI: 10.3390/biom4041045 -
Journal of Experimental Zoology. Part... Dec 2020Understanding host immune function and ecoimmunology is increasingly important at a time when emerging infectious diseases (EIDs) threaten wildlife. One EID that has... (Review)
Review
Understanding host immune function and ecoimmunology is increasingly important at a time when emerging infectious diseases (EIDs) threaten wildlife. One EID that has emerged and spread widely in recent years is chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), which is implicated unprecedented amphibian declines around the world. The impacts of Bd have been severe for many amphibian species, but some populations have exhibited signs of persistence, and even recovery, in some regions. Many mechanisms may underpin this pattern and amphibian immune responses are likely one key component. Although we have made great strides in understanding amphibian immunity, the complement system remains poorly understood. The complement system is a nonspecific, innate immune defense that is known to enhance other immune responses. Complement activation can occur by three different biochemical pathways and result in protective mechanisms, such as inflammation, opsonization, and pathogen lysis, thereby providing protection to the host. We currently lack an understanding of complement pathway activation for chytridiomycosis, but several studies have suggested that it may be a key part of an early and robust immune response that confers host resistance. Here, we review the available research on the complement system in general as well as amphibian complement responses to Bd infection. Additionally, we propose future research directions that will increase our understanding of the amphibian complement system and other immune responses to Bd. Finally, we suggest how a deeper understanding of amphibian immunity could enhance the conservation and management of amphibian species that are threatened by chytridiomycosis.
Topics: Amphibians; Animals; Batrachochytrium; Complement System Proteins; Mycoses
PubMed: 33052039
DOI: 10.1002/jez.2419