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opencc-zeroMar 2022View details →

Amphibian resistance to chytridiomycosis increases following low virulence chytrid fungal infection or drug-mediated clearance

Amphibian biodiversity is experiencing ongoing declines due in part to the infectious disease, chytridiomycosis. Efforts to mitigate the effects of the causal agent of chytridiomycosis, Batrachochytrium dendrobatidis (Bd), in the wild have not been wholly effective. Translocations are an important management tool for amphibians, and immunizations represent a possible strategy for preparing amphibians for release across a landscape where Bd exists. We evaluated the utility of using an isolate of Bd that was shown to be hypovirulent to the relict leopard frog (Rana onca) as a transmissible inoculum for promoting chytridiomycosis-resistance. We conducted a cohousing experiment to determine if the isolate we used could be passed between R. onca without increasing in virulence. We then followed with an experiment where frogs that were exposed to the hypovirulent isolate were then challenged with a virulent Bd isolate. In other experiments, we evaluated whether Bd infections followed by clearance with itraconazole (an antifungal) could increase resistance to chytridiomycosis in R. onca and Rana pipiens (northern leopard frog). We found that our hypovirulent Bd inoculation was transmissible between hosts, did not cause chytridiomycosis, and was effective at increasing chytridiomycosis-resistance. Rana onca inoculated with the hypovirulent Bd isolate had lower pathogen burdens and were 55 times more likely to survive infections by a virulent Bd isolate than non-inoculated frogs. For both species, prior exposure to Bd followed by infection clearance with itraconazole resulted in significantly increased survivorship and lower pathogen burdens as compared to controls that had no prior Bd exposure. Rana onca that were previously exposed to Bd were more than 15 times more likely to survive infections. Previously exposed R. pipiens survived in higher proportions than controls, but with weaker statistical support.

opencc-zeroApr 2022View details →

Area of habitat maps for amphibians and reptiles of Italy

Area of Habitat (AOH) maps reveal the distribution of the habitat available to the species within their geographic range. Information on the distribution of species' habitats can help identify sites where viable populations of a species are found. We produced high resolution (100 m), freely accessible global area of habitat maps for 60 species of reptiles and amphibians distributed in Italy, which represent 60% of all Italian amphibian and reptile species. AOH maps can be used as a reference for conservation planning and can help monitoring habitat loss, which is known to be a major threat to many reptile and amphibian species in Europe.

Figure 7 in Cranial skeletogenesis of one of the largest amphibians, Andrias japonicus, provides insight into ontogenetic adaptations for feeding in salamanders

Figure 7. Evolutionary allometry of cranial shape based on multivariate regression of shape on log10-transformed centroid size. Each point represents a specimen of Andrias japonicus (pink), Hynobius nebulosus (blue), Pleurodeles waltl (green) or Ambystomamexicanum (orange).Correlation coefficient, r = 0.874; P <0.05. The regression slopes are as follows: An. japonicus = 0.076, H. nebulosus = 0.088, P. waltl = 0.090 and Am. mexicanum = 0.035.

Figure 4 in Cranial skeletogenesis of one of the largest amphibians, Andrias japonicus, provides insight into ontogenetic adaptations for feeding in salamanders

Figure 4. Select phases of cranial skeletogenesis (ventral view) in Andrias japonicus, Hynobius nebulosus, Pleurodeles waltl and Ambystoma mexicanum. Pink elements are bone. Blue elements are cartilage. Scale bars are 1 mm, except for the 10 mm scale bar for phase XIII An. japonicus. Abbreviations: cl, columella; exo, exoccipital; fr, frontal; ma, maxilla; na, nasal; oc, otic capsule; opi, opisthotic, osph, orbitosphenoid; pa, parietal; pfr, prefrontal; pma, premaxilla; po, prootic; psph, parasphenoid; pt, pterygoid; q, quadrate; seth, sphenothmoid; sq, squamosal; vo, vomer.

Figure 2 in Cranial skeletogenesis of one of the largest amphibians, Andrias japonicus, provides insight into ontogenetic adaptations for feeding in salamanders

Figure 2. Cranial skeletogenesis in the Japanese giant salamander, Andrias japonicus. Cranial bones and cartilages are shown for eight of 12 developmental phases. Scale bars: 1 mm. Abbreviations: cl, columella; exo, exoccipital; fr, frontal; ma, maxilla; na, nasal; oc, otic capsule; osph, orbitosphenoid; pa, parietal; pfr, prefrontal; pma, premaxilla; psph, parasphenoid; pt, pterygoid; q, quadrate; seth, sphenothmoid; sq, squamosal; vo, vomer.

Figure 5 in Cranial skeletogenesis of one of the largest amphibians, Andrias japonicus, provides insight into ontogenetic adaptations for feeding in salamanders

Figure 5. Osteogenesis of the lower jaw and hyobranchial skeletons (ventral view) at larval (phases I or II) and postmetamorphosis (phases XII or XIII) stages of Andrias japonicus, Hynobius nebulosus, Pleurodeles waltl and Ambystoma mexicanum. Pink elements are bone. Blue elements are cartilage. Scale bars: 1 mm. Abbreviations: ang, angular; ar, anterior radial; art, articular; bb, basibranchial; cb, ceratobranchial; ce, ceratohyal; den, dentary; hb, hypobranchial; hc, hypohyal; pr, posterior radial.

Figure 1 in Cranial skeletogenesis of one of the largest amphibians, Andrias japonicus, provides insight into ontogenetic adaptations for feeding in salamanders

Figure 1. The skull of an adult Japanese giant salamander, Andrias japonicus. Left, dorsal view of the skull, with cartilages stained with Alcian Blue and bones with Alizarin Red. Scale bar: 10 mm. Right, landmarks on the skull. Abbreviations: exo, exoccipital; fr, frontal; ma, maxilla; na, nasal; osph, orbitosphenoid; pa, parietal; pfr, prefrontal; pma, premaxilla; pt, pterygoid; q, quadrate; sq, squamosal.

Figure 3 in Cranial skeletogenesis of one of the largest amphibians, Andrias japonicus, provides insight into ontogenetic adaptations for feeding in salamanders

Figure 3. Cranial skeletogenesis (dorsal view) in Andrias japonicus, Hynobius nebulosus, Pleurodeles waltl and Ambystoma mexicanum. Pink elements are bone. Blue elements are cartilage. Scale bars are 1 mm, except those for phase XIII An. japonicus and Am. mexicanum, which are 10 mm. Abbreviations: cl, columella; exo, exoccipital; fr, frontal; ma, maxilla; na, nasal; oc, otic capsule; opi, opisthotic, osph, orbitosphenoid; pa, parietal; pfr, prefrontal; pma, premaxilla; po, prootic; psph, parasphenoid; pt, pterygoid; q, quadrate; seth, sphenothmoid; sq, squamosal; vo, vomer.

opencc-zeroMay 2022View details →

Localized carry-over effects of pond drying on survival, growth, and pathogen defenses in amphibians

Climate change is increasing variability in precipitation patterns in many parts of the globe. Unpredictable changes in water availability can be particularly challenging for organisms that rely on precipitation-fed water sources for completing their life cycle, such as many amphibian species. Although developmental plasticity can mitigate the impacts of changing environments for some species, this strategy can come at a cost to other fitness-linked traits, such as immune function. We investigated localized variation in the capacity to respond to pond drying and evaluated whether developmental responses induced carry-over effects in disease susceptibility in three leopard frog species (Rana [Lithobates] pipiens and R. sphenocephala; two populations each, and one population of R. chiricahuensis). Using mesocosms located near the site of collection (<15 km away) in five regions spanning a latitudinal gradient, we raised tadpoles under simulated fast-drying, slow-drying, or constant water levels. After metamorphosis, we characterized several aspects of the skin microbiome, immune function, and response to exposure to the fungal pathogen Batrachochytrium dendrobatidis (Bd). Note that for R. chiricahuensis, the only carry-over effect measured was response to Bd exposure, for which we observed no effects of pond drying. We found that developmental plasticity in response to drying was rare, except in the southernmost population of R. sphenocephala. In this location, tadpoles responded by accelerating development, and frogs with shorter larval periods developed more severe infections following Bd exposure post-metamorphosis, suggesting a trade-off between surviving pond drying and pathogen defense investment. In the three other locations, a lack of accelerated metamorphosis in drying treatments was accompanied by increased mortality, decreased anti-Bd function of the microbiome, and/or greater Bd infection after exposure. Overall, results suggest that faster drying conditions will likely have negative impacts on amphibians with long larval periods, both directly and indirectly via carry-over effects. Because effects of drying exposure were not uniform within a species, our findings suggest local responses may not be generalizable to other regions of the range. These multifaceted effects of climate change on pathogen defenses are increasingly relevant as emerging infectious diseases threaten global biodiversity.

opencc-zeroMay 2019View details →

Data from: Latitudinal divergence in a wide-spread amphibian: contrasting patterns of neutral and adaptive genomic variation

Stochastic effects from demographic processes and selection are expected to shape the distribution of genetic variation in spatially heterogeneous environments. As the amount of genetic variation is central for long-term persistence of populations, understanding how these processes affect variation over large-scale geographic gradients is pivotal. We investigated the distribution of neutral and putatively adaptive genetic variation, and reconstructed demographic history in the moor frog (Rana arvalis) using 136 individuals from 15 populations along a 1700 km latitudinal gradient from northern Germany to northern Sweden. Using ddRAD-seq we obtained 27590 SNPs, and identified differentiation outliers and SNPs associated with growing season length. Populations grouped into a southern and a northern cluster, representing two phylogeographical lineages from different post-glacial colonization routes. Hybrid index estimation and demographic model selection showed strong support for a southern and northern lineage and evidence of gene flow between regions located on each side of a contact zone. However, patterns of past gene flow over the contact zone differed between neutral and putatively adaptive SNPs. While neutral nucleotide diversity was higher along the southern than the northern part of the gradient, nucleotide diversity in differentiation outliers showed the opposite pattern suggesting differences in the relative strength of selection and drift along the gradient. Variation associated with growing season length decreased with latitude along the southern part of the gradient, but not along the northern part where variation was lower, suggesting stronger climate-mediated selection in the north. Outlier SNPs included loci involved in immunity and developmental processes.

opencc-zeroDec 2012View details →

Data from: Forests as promoters of terrestrial life history strategies in East African amphibians

Many amphibian lineages show terrestrialization of their reproductive strategy and breeding is partially or completely independent of water. A number of causal factors have been proposed for the evolution of terrestrialized breeding. While predation has received repeated attention as a potential factor, the influence of others such as habitat has never been tested using appropriate data or methods. Using a dataset that comprises 180 amphibian species from various East African habitats, we tested whether species occurring in different habitats show different patterns of terrestrialization in their breeding strategy. We recovered a significant association between terrestrialized breeding strategies and forest habitats. In general, forest seems to act as a facilitator, providing a permissive environment for the evolution of terrestrialized breeding strategies. However, while terrestrial oviposition is strongly correlated with lowland and montane forest habitat, complete terrestrial development is significantly correlated with montane forest only, indicating different selective pressures acting at different steps towards complete terrestrial development.

opencc-zeroJul 2022View details →

Supplementary material 1 from: Krzikowski M, Nguyen TQ, Pham CT, Rödder D, Rauhaus A, Le MD, Ziegler T (2022) Assessment of the threat status of the amphibians in Vietnam - Implementation of the One Plan Approach. Nature Conservation 49: 77-116. https://doi.org/10.3897/natureconservation.49.82145

Assessment of the threat status of the amphibians in Vietnam - Implementation of the One Plan Approach

opencc-zeroJul 2022View details →

Natural history predicts patterns of thermal vulnerability in amphibians from the Atlantic rainforest of Brazil_supporting information

In the Brazilian Atlantic Rainforest (AF), amphibians (625 species) face habitat degradation leading to stressful thermal conditions that constrain animal activity (e.g. foraging, reproduction). Data on thermal ecology for these species is still scarce. We tested the hypothesis that environmental occupation affects the thermal tolerance of amphibian species more than their phylogenetic relationships. We evaluated patterns of thermal tolerance of 47 amphibian species by assessing critical thermal maxima and warming tolerances, relating these variables with ecological covariates (e.g. adult macro- and microhabitat and site of larval development). We used mean and maximum environmental temperature, ecological covariates, and morphological measurements in the phylogenetic generalized least squares models selection to evaluate which traits better predict thermal tolerance. We did not recover phylogenetic signal under a Brownian model; our results point to a strong association between critical thermal maxima and habitat and development site. Forest species were less tolerant to warm temperatures than open area or generalist species. Species with larvae that develop in lentic environment were more tolerant than those from lotic ones. Thus, species inhabiting forest microclimates are more vulnerable to the synergistic effect of habitat loss and climatic change. We use radar charts as a quick evaluation tool for thermal risk diagnoses using aspects of natural history as axes.

opencc-zeroSep 2022View details →

Ranavirus infection-induced avoidance behavior in wood frog juveniles: Do amphibians socially distance?

Hosts may limit exposure to pathogens through changes in behavior, such as avoiding infected individuals or contaminated areas. Here, we tested for a behavioral response to ranavirus infection in juvenile wood frogs (Rana sylvatica) because the majority of dispersal between populations occurs during this life stage. We hypothesized that if infections are transmissible and detectable at this life stage, then susceptibles would display avoidance behaviors when introduced to an infected conspecific. Despite no apparent signs of infection, we observed a greater distance between susceptible-infected pairs, compared to pairs of either two infected or two susceptible animals. Further, distances between susceptible-infected pairs were positively related to the infection intensity of the focal exposed frog, suggesting the cue to avoid infected conspecifics may become more detectable with more intense infections. Although we did not quantify whether transmission was affected by their distancing, our findings suggest that juvenile frogs have the potential to reduce terrestrial transmission of ranaviruses through avoidance behaviors.

opencc-zeroSep 2022View details →

Dispersal without drivers: Intrinsic and extrinsic variables have no impact on movement distances in a terrestrial amphibian

Dispersive movements are often thought to be multicausal and driven by individual body size, sex, conspecific density, environmental variation, personality and/or other variables. Yet such variables often do not account for most of the variation among dispersive movements in nature, leaving open the possibility that dispersion may be indeterministic. We assessed the amount of variation in 24 h movement distances that could be accounted for by potential drivers of displacement with a large empirical dataset of movement distances performed by Fowler's Toads (Anaxyrus fowleri) on the northern shore of Lake Erie at Long Point, Ontario (2002–2021, incl.). These toads are easy to sample repeatedly, can be identified individually and move parallel to the shoreline as they forage at night, potentially dispersing to new refuge sites. Using a linear mixed-effect model that incorporated random effect terms to account for sampling variance and inter-annual variation, we found that all potential intrinsic and extrinsic drivers of movement accounted for virtually none of the variation observed among 24 h distances moved by these animals, whether over short or large spatial scales. We examined the idea of movement personality by testing variance per individual toad and found no evidence of individuality in movement distances. We conclude that deterministic variables, whether intrinsic or extrinsic, neither can be shown to nor are necessary to drive movements in this population over all spatial scales. Stochastic, short-timescale movements, such as daily foraging movements, can instead accumulate over time to produce large spatial-scale movements that are dispersive in nature.

opencc-zeroSep 2022View details →

Experimental evidence that host species composition alters host-pathogen dynamics in a ranavirus-amphibian assemblage

Losses in biodiversity can alter disease risk through changes in host species composition. Host species vary in pathogen susceptibility and competence. Yet how changes in diversity alter host-pathogen dynamics remains unclear in many systems, particularly with respect to generalist pathogens. Amphibians are experiencing worldwide population declines linked to generalist pathogens, such as ranavirus, and thus represent an ideal group to investigate how host species composition affects disease risk. We conducted experiments where individuals in the laboratory and assemblages of three amphibian species (Pacific tree frogs, Pseudacris regilla; Cascades frogs, Rana cascadae; and Western toads, Anaxyrus boreas) or just A. boreas alone in outdoor mesocosms were exposed to ranavirus as larvae. In laboratory experiment, we observed low survival and high viral loads in P. regilla compared to the other species suggesting that this species was highly susceptible to the pathogen. In the mesocosm experiment, we observed 41% A. boreas mortality when alone and 98% mortality when maintained with P. regilla and R. cascadae. Our results suggest that the presence of highly susceptible species can alter disease dynamics across multiple species, potentially increasing infection risk and mortality in co-occurring species.

Fig. 3 in Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity

Fig. 3. Timing of chytridiomycosis-associated amphibian declines. (A) Declines by year. Bars indicate the number of declines in a given year, stacked by decline severity. For species for which the exact year of decline is uncertain, the figure shows the middle year of the interval of uncertainty, as stated by experts or inferred from available data. (B) Cumulative declines. Curves indicate the cumulative number of declines in each decline-severity category over time. In (A) and (B), the arrows mark the discovery of chytridiomycosis in 1998.

Fig. 2 in Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity

Fig. 2. Taxonomic distribution of chytridiomycosis-associated amphibian declines. Each bar represents one species, and color denotes the severity of its decline. Concentric circles indicate, from inner to outer, order (Caudata or Anura), family, and genus. Full names are given only for families and genera that include>5 and>2 species, respectively; details for all taxa are in table S4. Within each taxonomic level, sublevels are ordered alphabetically. Protruding bars indicate species for which there is evidence of recovery. [Photo credits (left to right): Telmatobius bolivianus, I.D.l.R.; Atelopus zeteki, B.G.; and Craugastor crassidigitus, B.G.]

Fig. 4 in Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity

Fig. 4. Severity of chytridiomycosis-associated amphibian declines in relation to the geographic and elevational ranges of species. (A) Declines in relation to geographic range. Each dot indicates a species, located randomly along the perimeter of a circle with radius equal to the log10 of the species's geographic range in kilometers squared. (B) Declines in relation to elevational range. Horizontal bars, boxes, and vertical bars indicate, respectively, mean, first and second quartiles, and 95% quantiles of elevation ranges within each category of decline severity.

Fig. 1 in Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity

Fig. 1. Global distribution of chytridiomycosis-associated amphibian species declines. Bar plots indicate the number (N) of declined species, grouped by continental area and classified by decline severity. Brazilian species are plotted separately from all other South American species (South America W); Mesoamerica includes Central America, Mexico, and the Caribbean Islands; and Oceania includes Australia and New Zealand. No declines have been reported in Asia. n, total number of declines by region. [Photo credits (clockwise from top left): Anaxyrus boreas, C. Brown, U.S. Geological Survey; Atelopus varius, B.G.; Salamandra salamandra, D. Descouens, Wikimedia Commons; Telmatobius sanborni, I.D.l.R; Cycloramphus boraceiensis, L.F.T.; Cardioglossa melanogaster, M.H.; and Pseudophryne corroboree, C. Doughty]