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opencc-zeroApr 2022View details →

Supplementary data from 'Predicting the distribution of Australian frogs and their overlap with Batrachochytrium dendrobatidis under climate change'

Aim: Amphibians, with over 40% of assessed species listed as threatened, are disproportionately at risk in the global extinction crisis. Among the many factors implicated in the current and ongoing loss of amphibian biodiversity are climate change and the disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd). These two threats are of particular concern in Australia, where Bd has been implicated in the declines of at least 43 frog species, and climate change is emerging as an additional threat. Here, we explore how climate change is likely to affect the distributions of Australian frog species and Bd to the year 2100, as well as how the spatial and climatic niche overlap between <a>chytridiomycosis-declined </a>frogs and Bd could shift. Location: Australia Methods: We used species distribution modelling to infer the current and future distribution of 141 Australian frog species and Bd, under two emissions scenarios. We used metrics of niche similarity, including Schoener's D and the Niche Margin Index, to quantify predicted alterations to spatial interactions between Bd and frog species. Results: Climate change is likely to have a variable impact on frog distributions in Australia, with some 23 and 47 species, primarily in southern Australia, predicted to lose at least 30% of their current distributions under low and high emissions scenarios, respectively. In contrast, 69 and 68 species, respectively, have potential to increase their distributions, primarily in northern Australia. While the distribution of Bd is predicted to decrease, the proportional spatial and niche overlap between Bd and susceptible frog species is predicted to remain little changed, and in some cases, to increase. Main conclusions: Although effects will be variable across the continent, climate change is likely to be a threatening factor to a number of Australian frog species. Additionally, chytridiomycosis is likely to remain a significant threat to many frog species, as any reductions to the pathogen's distribution largely coincide with geographic range contractions of chytridiomycosis-susceptible species.

opencc-zeroAug 2022View details →

Recovered frog populations coexist with endemic Batrachochytrium dendrobatidis despite load-dependent mortality

Novel infectious diseases, particularly those caused by fungal pathogens, pose considerable risks to global biodiversity. The amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) has demonstrated the scale of the threat, having caused the greatest recorded loss of vertebrate biodiversity attributable to a pathogen. Despite catastrophic declines on several continents, many affected species have experienced population recoveries after epidemics. However, the potential ongoing threat of endemic Bd in these recovered or recovering populations is still poorly understood. We investigated the threat of endemic Bd to frog populations that recovered after initial precipitous declines, focusing on the endangered rainforest frog Mixophyes fleayi. We conducted extensive field surveys over four years at three independent sites in eastern Australia. First, we compared Bd infection prevalence and infection intensities within frog communities to reveal species-specific infection patterns. Then, we analyzed capture-recapture data of M. fleayi to estimate the impact of Bd infection intensity on apparent mortality rates and Bd infection dynamics. We found that M. fleayi had lower infection intensities than sympatric frogs across the three sites, and cleared infections at higher rates than they gained infections throughout the study period. By incorporating time-varying individual infection intensities, we show that healthy M. fleayi populations persist despite increased apparent mortality associated with infrequent high Bd loads. Infection dynamics were influenced by environmental conditions, with Bd prevalence, infection intensity, and rates of gaining infection associated with lower temperatures and increased rainfall. However, mortality remained constant year-round despite these fluctuations in Bd infections, suggesting major mortality events did not occur over the study period. Together, our results demonstrate that while Bd is still a potential threat to recovered populations of M. fleayi, high rates of clearing infections and generally low average infection loads likely minimize mortality caused by Bd. Our results are consistent with pathogen resistance contributing to the coexistence of M. fleayi with endemic Bd. We emphasize the importance of incorporating infection intensity into disease models rather than infection status alone. Similar population and infection dynamics likely exist within other recovered amphibian-Bd systems around the globe, promising longer-term persistence in the face of endemic chytridiomycosis.

Fig. 2. Photographs. A in Chiggers (Acariformes: Trombiculoidea) do not increase rates of infection by Batrachochytrium dendrobatidis fungus in the endemic Dwarf Mexican Treefrog Tlalocohyla smithii (Anura: Hylidae)

Fig. 2. Photographs. A: restrained T. smithii specimen; B: anatomical areas of host (T.smithii) parasitized by Trombiculoidea chiggers; C: another specimen of T smithii in its natural habitat.

Fig. 1. Study area, showing November 2014 and 2016 in Chiggers (Acariformes: Trombiculoidea) do not increase rates of infection by Batrachochytrium dendrobatidis fungus in the endemic Dwarf Mexican Treefrog Tlalocohyla smithii (Anura: Hylidae)

Fig. 1. Study area, showing November 2014 and 2016 sampling sites. Gray and white circles show presence or absence of Batrachochytrium dendrobatidis. Sampling sites in 2010 and 2011 show fungus presence, reported by Cortes in 2014.

Fig. S2. E in Comparison of in vitro methods to inhibit growth of a virulent strain of Batrachochytrium dendrobatidis (Longcore, Pessier, and Nichols 1999)

Fig. S2. E. coli-violacein transformations. Violacein gene transformations of E. coli. (A) Example of NEB5-alpha-pJP1000 colony growth after 24 h post heat shock transformation. Each week, transformants were passed by re-streaking onto fresh agar and incubated at 37 °C for 24 h. (B) NEB5-alpha-pPSXvio+, (C) NEB5-alpha-pPSXvio++.

Fig. 3 in Comparison of in vitro methods to inhibit growth of a virulent strain of Batrachochytrium dendrobatidis (Longcore, Pessier, and Nichols 1999)

Fig. 3. Microscopic images (40x) of Bd challenge assays. (A) Microbacterium, (B) Micrococcaceae, and (C) recombinant E. coli- vio+. Vertical arrows point to the Bd lawn and horizontal arrows point to the left side of the bacterial streak. Absence of Bd lawn within field of view indicates the inhibitory effect from the bacterial streak. Approximate diameter of field of view ~0.5 mm.

Fig. S1. Toad skin swab cultures. Culture plates from A in Comparison of in vitro methods to inhibit growth of a virulent strain of Batrachochytrium dendrobatidis (Longcore, Pessier, and Nichols 1999)

Fig. S1. Toad skin swab cultures. Culture plates from A. boreas skin swabs after three days incubation at 25 °C.

Fig. 1. The Kruskal-Wallis rank sum test for the boxplot returned a in Comparison of in vitro methods to inhibit growth of a virulent strain of Batrachochytrium dendrobatidis (Longcore, Pessier, and Nichols 1999)

Fig. 1. The Kruskal-Wallis rank sum test for the boxplot returned a chi-squared value = 2, degrees of freedom (df) = 2, and P = 0.3679. The Wilcoxon rank sum test for the positive control and the highest concentration of amphotericin B returned W = 9, P = 0.1. These analyses show that the alternative hypothesis is true and assumes that there is information in the magnitudes and signs of the differences between paired observations, because the mean (location shift) is not equal to 0. Observed differences in mean cell count between the three groups (0.0, 1.6, and 3.2 µg/mL) are not statistically significant (P> 0.05).

Fig. 2 in Comparison of in vitro methods to inhibit growth of a virulent strain of Batrachochytrium dendrobatidis (Longcore, Pessier, and Nichols 1999)

Fig. 2. (A) and (B) Duplicate Bd negative controls, (C) E. coli-JP1000 (left bacterial streak) and Bacillus sp. (right bacterial streak), (D) E. coli-JP1000 displaying a clear ZOI surrounding the bacterial streak, (E) E. coli control.

opencc-by-4.0Aug 2014View details →

Fig. 2 in High prevalence of Batrachochytrium dendrobatidis in an Andean frog community (Reserva Las Gralarias, Ecuador)

Fig. 2. Significant Bd infection differences in amphibians according to reproductive modes, habitat use, and taxonomy. P values are reported for 2012 and 2013; significance is noted by ** (p <0.01) and *** (p <0.001).

opencc-by-4.0Nov 2014View details →

Figure 1. A in Field surveys in Western Panama indicate populations of Atelopus varius frogs are persisting in regions where Batrachochytrium dendrobatidis is now enzootic

Figure 1. A female Harlequin frog, Atelopus varius. This species, classified as Critically Endangered by IUCN, has been found in small numbers in the mountains of Western Panama.

publicAug 2022View details →

Recovered frog populations coexist with endemic Batrachochytrium dendrobatidis despite load-dependent mortality

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publicApr 2022View details →

Supplementary data from 'Predicting the distribution of Australian frogs and their overlap with Batrachochytrium dendrobatidis under climate change'

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opencc-zeroJan 2021View details →

Prevalence of Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans in thre Hoang Lien Range, northwest Vietnam

This study aims to investigate the presence of the amphibian chytrid fungi Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) in the <a name="_Hlk45376654">Hoang Lien Range, northwest Vietnam </a>as well as any patterns in Bd infection in space, time and host species over a five-year sampling period. This study also aims to investigate the presence of Bsal in the Hoang Lien Range.

opencc-zeroApr 2022View details →

Synthesis of batrachochytrium dendrobatidis infection in South America: amphibian species under risk and areas to focus research and disease mitigation

Amphibian chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), has been recognized as the infectious disease causing the most catastrophic loss of biodiversity known to science, with South America being the most impacted region. We tested whether Bd prevalence is distributed among host taxonomy, ecoregion, conservation status and habitat preference in South America. Here we provide a synthesis on the extent of Bd infection across South America based on 21,648 molecular diagnostic assays, roles of certain species in the epidemiology of Bd and explore its association with the reported amphibian catastrophic declines in the region. We show that Bd is widespread, with a continental prevalence of 23.2%. Its occurrence in the region shows a phylogenetic signal and the probability of infection is determined by ecoregion, preferred habitat, and extinction risk hosts' traits. The taxa exhibiting highest Bd occurrence, were mostly aquatic amphibians, including Ranidae, Telmatobiidae, Hylodidae, Calyptocephalellidae and Pipidae. Surprisingly, families exhibiting unusually low Bd prevalence included species in which lethal chytridiomycosis and population declines have been described (genus Atelopus, Rhinoderma and Eleutherodactylus). Higher than expected prevalence of Bd occurred mainly in amphibians living associated with mountain environments in the Andes and Atlantic forests, reflecting highly favourable Bd habitats in these areas. Invasive amphibian species (e.g. Lithobates catesbeianus and Xenopus laevis) exhibited high Bd prevalence, as thus we suggest using these as sentinels to understand their potential role as reservoirs, vectors or spreaders of Bd that can be subjected to management. Our results guide on the prioritization of conservation actions to prevent further biodiversity loss due to chytridiomycosis in the world's most amphibian diverse region.

opencc-zeroApr 2022View details →

Host identity matters – up to a point: the community context of Batrachochytrium dendrobatidis transmission

The level of detail on host communities needed to understand multi-host parasite invasions is an unresolved issue in disease ecology. Coarse community metrics that ignore functional differences between hosts, like host species richness, can be good predictors of invasion outcomes. Yet, if host species vary in the extent to which they maintain and transmit infections, then explicitly accounting for those differences may be important. Through controlled mesocosm experiments and modelling, we show that interspecific differences between host species are important for community-wide infection dynamics of the multi-host fungal parasite of amphibians, Batrachochytrium dendrobatidis (Bd), but only up to a point. The most abundant host species in our system, fire salamander larvae (Salamandra salamandra), did not maintain or transmit infections. Rather, two less abundant 'auxiliary' host species, Iberian tree frog (Hyla molleri) and spiny toad (Bufo spinosus) larvae, maintained and transmitted Bd. Frogs had the highest mean rates of Bd shedding, giving them the highest contributions to R0. Toad contributions to R0 were substantial however, and when examining community-level patterns of infection and transmission, the effects of frogs and toads were similar. Specifying more than just host species richness to distinguish salamanders from auxiliary host species was critical for predicting community-level Bd prevalence and transmission. Distinguishing frogs from toads, however, did not improve predictions. These findings demonstrate limitations to the importance of host species identities in multi-host infection dynamics. Host species that exhibit different functional traits, like susceptibility and infectiousness, may play similar epidemiological roles in the broader community.

opencc-zeroJun 2022View details →

Data from: Metabolites from the fungal pathogen Batrachochytrium dendrobatidis (Bd) reduce Bd load in Cuban treefrog tadpoles

Batrachochytrium dendrobatidis (Bd) has been associated with massive amphibian population declines worldwide. Wildlife vaccination campaigns have proven effective for mitigating damage from other pathogens, and there is evidence that adult frogs can acquire resistance to Bd when exposed to killed Bd zoospores and the metabolites they produced. Here, we investigated whether Cuban treefrogs tadpoles (Osteopilus septentrionalis) can gain protection from Bd through exposure to a prophylaxis treatment composed of killed zoospores or soluble Bd metabolites. We used a 2x2 factorial design, crossing the presence or absence of killed zoospores with the presence or absence of Bd metabolites. All hosts were subsequently exposed to live Bd to evaluate susceptibility. Exposure to killed zoospores did not induce a protective response. However, tadpoles exposed to Bd metabolites had significantly lower Bd intensity and prevalence than tadpoles that were not exposed to metabolites. The metabolites Bd produce pose no risk of Bd infection and therefore make an epidemiologically safe prophylaxis treatment, protecting tadpoles against Bd. This work provides a promising potential for protecting amphibians in the wild as a disease management strategy for controlling Bd associated declines.