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EcoHealth Dec 2023Batrachochytrium dendrobatidis (Bd), the causative agent of the devastating global amphibian disease chytridiomycosis, was not projected to threaten amphibians in hot...
Batrachochytrium dendrobatidis (Bd), the causative agent of the devastating global amphibian disease chytridiomycosis, was not projected to threaten amphibians in hot and arid regions due to its sensitivity to heat and desiccation. However, Bd is being detected more frequently than ever in hot and arid regions of Australia and the USA, challenging our current understanding of the environmental tolerances of the pathogen under natural conditions. We surveyed for Bd in an extremely hot and arid portion of the Sonoran Desert, where the pathogen is not projected to occur, and related presence and prevalence of the pathogen to local environmental conditions. We collected eDNA samples from isolated desert water sites including six tinajas and 13 catchments in June and August of 2020 and swabbed a total of 281 anurans of three species (red-spotted toad Anaxyrus punctatus, Couch's spadefoot Scaphiopus couchii, and the Sonoran Desert toad Incillius alvarius) across five catchments and six tinajas from June to September of 2020. Overall, Bd occurred at 68.4% of sites, despite extreme heat and aridity routinely exceeding tolerances established in laboratory studies. Average summer maximum air and water temperatures were 40.7°C and 30.7°C, respectively, and sites received an average of just 16.9 mm of precipitation throughout the summer monsoon season. Prevalence was low (5.7%) across species and life stage. Our results demonstrate that Bd is capable of persisting and infecting amphibians beyond its projected range, indicating a need to account for higher thermal tolerances when quantifying risk of Bd presence and infection.
Topics: Animals; Batrachochytrium; Chytridiomycota; Amphibians; Bufonidae; Temperature; Water
PubMed: 38243042
DOI: 10.1007/s10393-023-01668-1 -
Molecular Reproduction and Development Oct 2019It is a widely held belief that environmental contaminants contribute to the decline of amphibian populations. By spending most of their early life in water and later... (Review)
Review
It is a widely held belief that environmental contaminants contribute to the decline of amphibian populations. By spending most of their early life in water and later stages on the land, amphibians face a constant risk of exposure to pesticides and other chemical pollutants in both aquatic and terrestrial environments. This review presents an overview of the studies carried out in Italian amphibians to highlight hazardous effects of bioaccumulation of chemical pollutants in juveniles and adults in various contaminated environments. Further, the studies in the laboratory setting assessing the effects of chemical pollutants on reproductive and developmental processes are reported. These studies and their relative references have been summarized in a tabular form. Three prominent contaminant groups were identified: herbicides, insecticides, and fungicides; and only a few works reported the effects of other chemical pollutants. Each pollutant group has been delegated to a section. All through the literature survey, it is seen that interest in this topic in Italy is very recent and sparse, where only a few anuran and caudata species and only some chemical pollutants have been studied.
Topics: Amphibians; Animals; Environmental Pollutants; Italy; Life Cycle Stages; Pesticides; Reproduction
PubMed: 31111596
DOI: 10.1002/mrd.23165 -
Philosophical Transactions of the Royal... Mar 2024Environmental variation in the Anthropocene involves several factors that interfere with endocrine systems of wildlife and humans, presenting a planetary boundary of... (Review)
Review
Environmental variation in the Anthropocene involves several factors that interfere with endocrine systems of wildlife and humans, presenting a planetary boundary of still unknown dimensions. Here, we focus on chemical compounds and other impacts of anthropogenic and natural origins that are adversely affecting reproduction and development. The main sink of these endocrine disruptors (EDs) is surface waters, where they mostly endanger aquatic vertebrates, like teleost fish and amphibians. For regulatory purposes, EDs are categorized into EATS modalities (oestrogenic, androgenic, thyroidal, steroidogenesis), only addressing endocrine systems being assessable by validated tests. However, there is evidence that non-EATS modalities-and even natural sources, such as decomposition products of plants or parasitic infections-can affect vertebrate endocrine systems. Recently, the disturbance of natural circadian light rhythms by artificial light at night (ALAN) has been identified as another ED. Reviewing the knowledge about EDs affecting teleosts and amphibians leads to implications for risk assessment. The generally accepted WHO-definition for EDs, which focuses exclusively on 'exogenous substances' and neglects parasitic infections or ALAN, seems to require some adaptation. Natural EDs have been involved in coevolutionary processes for ages without resulting in a general loss of biodiversity. Therefore, to address the 'One Health'-principle, future research and regulatory efforts should focus on minimizing anthropogenic factors for endocrine disruption. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.
Topics: Animals; Humans; Endocrine System; Amphibians; Vertebrates; Risk Assessment; Parasitic Diseases
PubMed: 38310939
DOI: 10.1098/rstb.2022.0505 -
Sexual Development : Genetics,... 2021The role of environmental factors in sexual differentiation in amphibians is not new. The effect of hormones or hormone-like compounds is widely demonstrated. However,... (Review)
Review
The role of environmental factors in sexual differentiation in amphibians is not new. The effect of hormones or hormone-like compounds is widely demonstrated. However, the effect of temperature has traditionally been regarded as something anecdotal that occurs in extreme situations and not as a factor to be considered. The data currently available reveal a different situation. Sexual differentiation in some amphibian species can be altered even by small changes in temperature. On the other hand, although not proven, it is possible that temperature is related to the appearance of sex-reversed individuals in natural populations under conditions unrelated to environmental contaminants. According to this, temperature, through sex reversal (phenotypic sex opposed to genetic sex), could play an important role in the turnover of sex-determining genes and in the maintenance of homomorphic sex chromosomes in this group. Accordingly, and given the expected increase in global temperatures, growth and sexual differentiation in amphibians could easily be affected, altering the sex ratio in natural populations and posing major conservation challenges for a group in worldwide decline. It is therefore particularly urgent to understand the mechanism by which temperature affects sexual differentiation in amphibians.
Topics: Amphibians; Animals; Humans; Sex Chromosomes; Sex Determination Processes; Sex Differentiation; Temperature
PubMed: 34000727
DOI: 10.1159/000515220 -
Nature Communications Nov 2022Amphibians have undergone important evolutionary transitions in reproductive modes and life-cycles. We compare large-scale macroevolutionary patterns in these...
Amphibians have undergone important evolutionary transitions in reproductive modes and life-cycles. We compare large-scale macroevolutionary patterns in these transitions across the three major amphibian clades: frogs, salamanders, and caecilians. We analyse matching reproductive and phylogenetic data for 4025 species. We find that having aquatic larvae is ancestral for all three groups and is retained by many extant species (33-44%). The most frequent transitions in each group are to relatively uncommon states: live-bearing in caecilians, paedomorphosis in salamanders, and semi-terrestriality in frogs. All three groups show transitions to more terrestrial reproductive modes, but only in caecilians have these evolved sequentially from most-to-least aquatic. Diversification rates are largely independent of reproductive modes. However, in salamanders direct development accelerates diversification whereas paedomorphosis decreases it. Overall, we find a widespread retention of ancestral modes, decoupling of trait transition rates from patterns of species richness, and the general independence of reproductive modes and diversification.
Topics: Animals; Phylogeny; Life Cycle Stages; Reproduction; Anura; Urodela
PubMed: 36396632
DOI: 10.1038/s41467-022-34474-4 -
Scientific Reports May 2024Amphibians are often recognized as bioindicators of healthy ecosystems. The persistence of amphibian populations in heavily contaminated environments provides an...
Amphibians are often recognized as bioindicators of healthy ecosystems. The persistence of amphibian populations in heavily contaminated environments provides an excellent opportunity to investigate rapid vertebrate adaptations to harmful contaminants. Using a combination of culture-based challenge assays and a skin permeability assay, we tested whether the skin-associated microbiota may confer adaptive tolerance to tropical amphibians in regions heavily contaminated with arsenic, thus supporting the adaptive microbiome principle and immune interactions of the amphibian mucus. At lower arsenic concentrations (1 and 5 mM As), we found a significantly higher number of bacterial isolates tolerant to arsenic from amphibians sampled at an arsenic contaminated region (TES) than from amphibians sampled at an arsenic free region (JN). Strikingly, none of the bacterial isolates from our arsenic free region tolerated high concentrations of arsenic. In our skin permeability experiment, where we tested whether a subset of arsenic-tolerant bacterial isolates could reduce skin permeability to arsenic, we found that isolates known to tolerate high concentrations of arsenic significantly reduced amphibian skin permeability to this metalloid. This pattern did not hold true for bacterial isolates with low arsenic tolerance. Our results describe a pattern of environmental selection of arsenic-tolerant skin bacteria capable of protecting amphibians from intoxication, which helps explain the persistence of amphibian populations in water bodies heavily contaminated with arsenic.
Topics: Animals; Arsenic; Microbiota; Skin; Amphibians; Bacteria; Permeability
PubMed: 38702361
DOI: 10.1038/s41598-024-60879-w -
Environmental Toxicology and Chemistry Mar 2022Emerging infectious disease outbreaks are one of multiple stressors responsible for amphibian declines globally. In the northeastern United States, ranaviral diseases...
Emerging infectious disease outbreaks are one of multiple stressors responsible for amphibian declines globally. In the northeastern United States, ranaviral diseases are prevalent in amphibians and other ectothermic species, but there is still uncertainty as to whether their presence is leading to population-level effects. Further, there is also uncertainty surrounding the potential interactions among disease infection prevalence in free-ranging animals and habitat degradation (co-occurrence of chemical stressors). The present study was designed to provide field-based estimates of the relationship between amphibian disease and chemical stressors. We visited 40 wetlands across three protected areas, estimated the prevalence of ranavirus among populations of larval wood frogs and spotted salamanders, and assessed chemical and biological stressors in wetland habitats and larval amphibians using a suite of selected bioassays, screening tools, and chemical analyses. Ranavirus was detected on larval amphibians from each protected area with an estimated occupancy ranging from 0.27 to 0.55. Considerable variation in ranavirus occupancy was also observed within and among each protected area. Of the stressors evaluated, ranavirus prevalence was strongly and positively related to concentrations of metalloestrogens (metals with the potential to bind to estrogen receptors) and total metals in wetland sediments and weakly and negatively related to total pesticide concentrations in larval amphibians. These results can be used by land managers to refine habitat assessments to include such environmental factors with the potential to influence disease susceptibility. Environ Toxicol Chem 2022;41:781-791. © 2022 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.
Topics: Amphibians; Animals; Communicable Diseases, Emerging; Larva; Prevalence; Ranavirus; Ranidae; Wetlands
PubMed: 35040181
DOI: 10.1002/etc.5291 -
Environmental Microbiology Dec 2022Seasonal variation has been shown to influence symbiotic bacterial community composition and structure in amphibians. It is still unknown how the symbiotic bacterial...
Seasonal variation has been shown to influence symbiotic bacterial community composition and structure in amphibians. It is still unknown how the symbiotic bacterial community assembly changes during different seasons, especially for amphibians who are particularly sensitive to environmental change. We found significant differences in the composition and diversity (alpha and beta diversity) of amphibian skin and gut bacteria. Co-occurrences network analysis showed that seasonal variation reduced the microbial network complexity of amphibians from summer to autumn. The normalized stochastic ratio (NST) and phylogenetic bin-based null model analysis (iCAMP) models showed that the same result that stochastic processes was the major factor regulating the symbiotic bacterial community assembly mechanisms of amphibians. From summer to autumn, the symbiotic bacterial community assembly mechanisms declined in the contribution of stochastic processes, while increasing in the contribution of deterministic processes. Dispersal limitation was the dominant microbial assembly mechanism, followed by homogeneous selection, and then heterogeneous selection in the symbiotic bacterial community communities of amphibians between summer and autumn. Furthermore, higher niche width of the symbiotic bacterial community of amphibians was found in summer than autumn. Overall, these results demonstrated that seasonal variation influenced amphibian symbiotic bacterial community between summer and autumn.
Topics: Animals; Seasons; Phylogeny; Bacteria; Amphibians; Stochastic Processes
PubMed: 36156840
DOI: 10.1111/1462-2920.16224 -
Comparative Biochemistry and... 2021The interpretation of thermal-gradient data depends on the behavioral drives reported or assumed, and on the underlying behavioral models explaining how such drives... (Review)
Review
The interpretation of thermal-gradient data depends on the behavioral drives reported or assumed, and on the underlying behavioral models explaining how such drives operate. The best-known example is positive thermotaxis, a thermoregulatory behavioral drive frequently linked to a dual set-point model of thermoregulation around a target range. This behavioral drive is often assumed as dominant among 'ectotherms', including amphibians. However, we argue that, because amphibians are extremely diverse, they may exhibit alternative behavioral drives in thermal gradients, and tackle this idea from two perspectives. First, we provide a historical review of original definitions and proposed limits for inference. Second, although caveats apply, we propose that a cross-study analysis of data of temperature settings of gradients and the temperatures selected by amphibians would corroborate alternative behavioral drives, including negative thermotaxis. Therefore, we analyzed published data focusing on such relationships and show that gradient temperature settings influence the temperatures selected by amphibians, with further effects of phylogeny and ontogeny. We conclude that thermal gradient experiments are outstanding tools to investigate behavioral drives, but no given drive can be assumed a priori unless additional information about thermoregulation is available. Based on the historical debate, we propose using selected temperatures and preferred temperatures as different concepts, the former merely operational and the second explicitly linked to positive thermotaxis (and thus compatible with dual set-point thermoregulation). Under this view, thermal preferences would stand for a hypothesis of a behavioral drive (positive thermotaxis) requiring formal testing. These considerations impact the scope for inference based on thermal gradient experiments, particularly ecological modeling and emerging disease.
Topics: Amphibians; Animals; Body Temperature Regulation; Temperature
PubMed: 33609807
DOI: 10.1016/j.cbpb.2021.110576 -
Journal of Genetics Dec 2019Amphibians show a very high level of diversity and endemism and are facing global declines from the past few decades. Studies have shown that the molecular tools can be... (Review)
Review
Amphibians show a very high level of diversity and endemism and are facing global declines from the past few decades. Studies have shown that the molecular tools can be helpful in their conservation efforts. In India, more than 80% of amphibians are endemic and most show a narrow range of distribution. Most of the Indian amphibians lack information on their genetic diversity. In this study, were view the overall trend on amphibian studies in India with the specific focus on conservation genetics. Overall, of the 173 studies, only 14 dealt with the conservation of amphibians through genetic tools and five studies estimated the genetic diversity or gene structure. Here, we discuss the gaps and provide future directions on how genetic studies can be helpful in Indian amphibian conservation.
Topics: Amphibians; Animals; Biodiversity; Conservation of Natural Resources; Databases, Factual; Genetic Markers; Genetic Variation; India; Phylogeography; Population Density
PubMed: 31819027
DOI: No ID Found