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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 -
Journal of Experimental Zoology. Part... Jan 2021Research on the thermal ecology and physiology of free-living organisms is accelerating as scientists and managers recognize the urgency of the global biodiversity... (Review)
Review
Research on the thermal ecology and physiology of free-living organisms is accelerating as scientists and managers recognize the urgency of the global biodiversity crisis brought on by climate change. As ectotherms, temperature fundamentally affects most aspects of the lives of amphibians and reptiles, making them excellent models for studying how animals are impacted by changing temperatures. As research on this group of organisms accelerates, it is essential to maintain consistent and optimal methodology so that results can be compared across groups and over time. This review addresses the utility of reptiles and amphibians as model organisms for thermal studies by reviewing the best practices for research on their thermal ecology and physiology, and by highlighting key studies that have advanced the field with new and improved methods. We end by presenting several areas where reptiles and amphibians show great promise for further advancing our understanding of how temperature relations between organisms and their environments are impacted by global climate change.
Topics: Amphibians; Animals; Body Temperature; Ecosystem; Embryo, Nonmammalian; Monitoring, Physiologic; Reptiles
PubMed: 32638552
DOI: 10.1002/jez.2396 -
Journal of Experimental Zoology. Part... Apr 2024This review article includes a literature review of synteny analysis of the amphibian gonadotropin-releasing hormone (GnRH) genes, the distribution of GnRH 1 and GnRH2... (Review)
Review
This review article includes a literature review of synteny analysis of the amphibian gonadotropin-releasing hormone (GnRH) genes, the distribution of GnRH 1 and GnRH2 neurons in the central nervous system of amphibians, the function and regulation of hypophysiotropic GnRH1, and the function of GnRH1 in amphibian reproductive behaviors. It is generally accepted that GnRH is the key regulator of the hypothalamic-pituitary-gonadal axis. Three independent GnRH genes, GnRH1, GnRH2, and GnRH3, have been identified in vertebrates. Previous genome synteny analyses suggest that there are likely just two genes, gnrh1 and gnrh2, in amphibians. In three groups of amphibians: Anura, Urodela, and Gymnophiona, the distributions of GnRH1 and GnRH2 neurons in the central nervous system have also been previously reported. Moreover, these neuronal networks were determined to be structurally independent in all species examined. The somata of GnRH1 neurons are located in the terminal nerve, medial septum (MS), and preoptic area (POA), and some GnRH1 neurons in the MS and POA project into the median eminence. In contrast, the somata of GnRH2 neurons are located in the midbrain tegmentum. In amphibians, GnRH1 neurons originate from the embryonic olfactory placode, while GnRH2 neurons originate from the midbrain. The characterization and feedback regulation mechanisms of hypophysiotropic GnRH1 neurons in amphibians, the involvement of GnRH1 in amphibian reproductive behavior, and its possible mechanism of action should be elucidated in future.
Topics: Animals; Gonadotropin-Releasing Hormone; Reproduction; Vertebrates; Amphibians
PubMed: 38084833
DOI: 10.1002/jez.2769 -
Nature Reviews. Microbiology Jun 2020Discovering that chytrid fungi cause chytridiomycosis in amphibians represented a paradigm shift in our understanding of how emerging infectious diseases contribute to... (Review)
Review
Discovering that chytrid fungi cause chytridiomycosis in amphibians represented a paradigm shift in our understanding of how emerging infectious diseases contribute to global patterns of biodiversity loss. In this Review we describe how the use of multidisciplinary biological approaches has been essential to pinpointing the origins of amphibian-parasitizing chytrid fungi, including Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans, as well as to timing their emergence, tracking their cycles of expansion and identifying the core mechanisms that underpin their pathogenicity. We discuss the development of the experimental methods and bioinformatics toolkits that have provided a fuller understanding of batrachochytrid biology and informed policy and control measures.
Topics: Amphibians; Animals; Biodiversity; Chytridiomycota; Genotype; Population Dynamics; Recombination, Genetic; Time Factors; Virulence
PubMed: 32099078
DOI: 10.1038/s41579-020-0335-x -
Development, Growth & Differentiation Dec 2022
Topics: Animals; Amphibians
PubMed: 36579413
DOI: 10.1111/dgd.12829 -
Development, Growth & Differentiation Aug 2022
Topics: Amphibians; Animals
PubMed: 36088539
DOI: 10.1111/dgd.12805 -
Development, Growth & Differentiation Oct 2023
Topics: Animals; Amphibians
PubMed: 37881023
DOI: 10.1111/dgd.12889