Batrachochytrium Research Articles

Chytridiomycosis in Sri Lanka: Predicting the future of a global amphibian hotspot

Abstract Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), constitutes a major threat to many amphibian species worldwide. Predicting the species and regions of highest geographical risk is critical for the early detection and mitigation of chytrid emergence. In this study, using a niche modelling approach, the most conducive habitat for Bd within Sri Lanka (a high‐risk zone) was modelled. The distribution of 69 amphibian species was then modelled and their overlap with the high‐risk zone (areaBd) was calculated. Using areaBd and a biotic index (BI), created using ecological traits of each species, a risk index (RI) was calculated. Using this RI, a high‐risk species index (HRSI) was developed to identify the species most at risk. The results indicate that the high elevations of Sri Lanka (>600 m a.s.l.) are highly conducive for Bd. The HRSI includes 35 species, with Minervarya greenii being the species most at risk. All species in the HRSI are globally Critically Endangered (n = 14) or Endangered (n = 21). We propose active conservation measures such as the routine monitoring of HRSI species and other proactive measures to identify and prevent the spread of Bd. We believe our findings would promote the establishment of pre‐emptive mitigation measures both within Sri Lanka and elsewhere, to counter the threat of chytridiomycosis and to conserve amphibian species.

Optimal management decisions are robust to unknown dynamics in an amphibian metapopulation plagued by disease

AbstractIdentifying conservation actions to recover threatened species can be challenging due to many ecological uncertainties. For example, major threats to a species' conservation are commonly known or suspected, but the specific impacts on population or metapopulation dynamics can be uncertain. This is frequently the case with emerging infectious diseases, including chytridiomycosis, a global driver of amphibian population declines caused by the fungal pathogens Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans. While these diseases are known to cause amphibian declines and extirpations, the mechanisms of their landscape‐scale spread are still largely unknown. Such uncertainty can lead to inaction which may jeopardize timely recovery of a species. Decision analysis is a pragmatic approach to making transparent and defensible decisions while dealing with uncertainties. We investigated whether optimal actions aimed at recovering boreal toad (Anaxyrus boreas boreas) metapopulations in the southern Rocky Mountains are robust to the unknown dynamics of Bd spread using value of information and regret analyses. Value of information is a decision‐analytic tool for calculating the value of new information in terms of performance on management objectives, while regret measures the cost of acting under incorrect information. We further conducted a stochastic sensitivity analysis to identify the relative effects of metapopulation parameters on system dynamics. We found optimal actions were robust to the unknown dynamics of Bd spread. While boreal toad breeding occurrence is highly sensitive to Bd distribution, the optimal decision is not. Resolving the unknown dynamics of Bd spread would lead to a minimal gain of less than one breeding toad subpopulation at the end of 50 years, given the currently available management actions. Applying a decision‐analytic framework coupled with value of information and regret analyses can help frame how uncertainties affect decisions in a way that empowers decision makers.

A Universal and Efficient Detection of Chytridiomycosis Infections in Amphibians Using Novel Quantitative PCR Markers

Chytridiomycosis is an infectious disease in amphibians caused by two chytrid fungi, Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal), and is the worst infectious disease known in wildlife so far. Worldwide spread of the disease has caused unprecedented loss of global amphibian diversity. Although some lineages of Bd are enzootic and are not as deadly as the pandemic lineage, nearly 40% of amphibian species are still declining globally due to chytridiomycosis. Efficient surveillance and monitoring of chytridiomycosis are the immediate safeguard against rapid declines or extinctions of amphibian populations. Previous studies showed that existing diagnostic assays were not sensitive to certain Bd haplotypes like those from Korea, China, India, Japan, and Brazil and thereby, there is a need for a universal, sensitive, specific, reproducible, and affordable diagnostic assay. We designed a one-step SYBR green-based quantitative polymerase chain reaction (nSYBR qPCR) for robust detection of Bd. It amplifies an 82 base-pair segment between the 5.8S rRNA and ITS2 of the Bd genome. The primer pair was tested in-silico on 40 isolates from four known Bd lineages. Using skin swab samples of wild amphibians and cultured zoospores from Australia and Panama, we compared the clinical specificity and sensitivity of the newly described primers to the existing TaqMan-based qPCR assay. From India, we used samples which had been previously tested with Nested PCR to validate the new primer pairs. The newly described primer pair was then tested on swab samples from Anura, Caudata and Gymnophiona from India. We report widespread chytridiomycosis with varying infection loads on them. The new assay showed comparable efficiency to the TaqMan-based qPCR assay. This diagnostic assay can facilitate widespread surveillance of chytridiomycosis where it has been previously absent, which may reveal several reservoirs of the pathogen and can improve our understanding of this important wildlife disease.

Introduced Mediterranean painted frogs (Discoglossus pictus) are possible supershedders of the fungus Batrachochytrium dendrobatidis in Catalonia (NE Spain)

Abstract In 2020 and 2021 we detected in Catalonia (NE Spain) six new episodes of mortality or presence of dying specimens in introduced Mediterranean painted frogs (Discoglossus pictus). All affected individuals were positive to the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). Histological examinations showed intense involvement of the superficial layers of the epidermis and qPCR analyses yielded infection loads greater than 100 000 genomic equivalents of zoospores. These results suggest that this introduced species could behave as a Bd ‘supershedder’, and recommend to control its expansion due to its important role in the dynamic of chytridiomycosis.

First report of chytridiomycosis in the Southern Yungas Andean forest: a threat to the endangered La Banderita marsupial frog Gastrotheca gracilis

This work reports the first record of Batrachochytrium dendrobatidis (Bd) infection in the endangered La Banderita marsupial frog Gastrotheca gracilis from the Southern Yungas Andean forest. We analysed swab samples from the oral discs of 20 tadpoles and histological sections from two post-metamorphic individuals. We found 60 % of the tadpoles to be infected, and the histological sections revealed the presence of zoosporangia of Bd in different maturation stages. The signs of infection confirm the presence of Bd, which may pose a threat to the endangered La Banderita marsupial frog populations. Keywords: conservation, Batrachochytrium dendrobatidis, chytridfungus infection, Hemiphractidae, tadpoles

Smaller size of harlequin toads from populations long exposed to the fungal disease chytridiomycosis

AbstractPathogens can exert great selective pressures on the life history traits of their hosts. Species experiencing high mortality throughout their adulthood can benefit from breeding earlier. Chytridiomycosis, a fungal disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), has been a major driver of extinction for harlequin toads (Atelopus) and continues to be frequent cause of adult mortality for species persisting with endemic infections. We compared the body size of Atelopus cruciger between a remnant population long exposed to Bd (post‐epidemic) and populations sampled before the presumed Bd outbreak in the late 80s (pre‐epidemic). Reproductive female and male toads from pre‐epidemic populations were significantly bigger than those from post‐epidemic populations at similar altitudes, suggesting that toads from post‐epidemic populations are breeding earlier. A significant positive relationship between body size and the number of eggs in oviducts suggests a trade‐off between the benefit of breeding earlier and the cost of smaller clutch sizes. This cost–benefit relationship is likely to change along elevation gradients because the number of eggs relative to body size tends to be lower at higher elevations. By breeding earlier harlequin toad populations long exposed to Bd can increase their demographic competence, particularly in lowland habitats, where the cost–benefit relationship of breeding earlier tends to be more favorable.Abstract in Spanish is available with online material.

Safe harbor: translocating California red‐legged frogs to a climate refuge in Yosemite National Park

Safe harbor: translocating California red‐legged frogs to a climate refuge in Yosemite National Park

Uncovering the hidden biodiversity of streams at the upper distribution limit of fish

AbstractAimBiodiversity changes can occur gradually or as distinct jumps as species distributions end and others begin. However, comprehensive assessments of freshwater biodiversity and how assemblages change along a continuum have been hindered by the connectivity and networked nature of streams and their large numbers of rare and cryptic species found there. We hypothesize that the boundary where fish distributions end marks an ecological shift in freshwater assemblages and could unify stream concepts.LocationTrask River watershed, Oregon, USA, temperate North America.TaxonFishes, amphibians, crayfishes, bivalves, mammals, pathogens.MethodsWe targeted freshwater species across taxa using multigene eDNA metabarcoding of 48 different DNA barcodes to identify assemblages to understand species patterns distributed along a longitudinal gradient in watersheds around the upper fish distribution boundary. Detections from multiple genetic sources improve the detection probability for rare species.ResultsWe detected a shift in the assemblage from lower reaches towards headwaters where fish distributions end, leading to fewer species across taxa at reduced eDNA signal. We uncovered a hidden biodiversity in watersheds by detecting a sparsely distributed amphibian pathogen Batrachochytrium dendrobatidis, the elusive mammal Mountain Beaver, fish species that went undetected using traditional approaches, and newly discovered cryptic lineages of sculpins. Salmonids were detected further upstream with eDNA than expected.Main conclusionsOur findings unify stream concepts owing to the marked species shift at the upper extent of fish elevating the importance of this boundary. The detection of salmonids further upstream suggests a distribution extension. The sculpin detections reveal a cryptic species complex with ramifications for fish conservation, potential pockets of endemism and possible identification of new species. We show extensive diversity in watersheds, some of which was previously hidden, transforming our understanding of species presence and distributions affecting our ability to track, protect and manage them across watersheds.

Exposure to Amphibian Chytrid Fungus Alters Terrestrial Growth and Feeding Rate in Metamorphic Anurans

Population declines and extinctions associated with infectious diseases of wildlife are increasing in both frequency and severity. Response to infectious disease varies among species and individuals, with some appearing asymptomatic and others experiencing rapid mortality. The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), has been associated with widespread population declines and species extinctions, yet in some geographic regions it elicits a range of sublethal responses that may influence population dynamics in ways that are currently not understood. Our central objective was to evaluate growth and feeding behavior of terrestrial juvenile American Toads (Anaxyrus americanus) and Northern Leopard Frogs (Lithobates pipiens) following exposure to Bd. We manipulated foraging effort through the presence or absence of refugia for prey. We found that both amphibian species grew less when exposed to the pathogen, though the mechanisms contributing to this effect appear not to be the same. American Toads ate equal to or more in feeding trials when exposed to Bd than when unexposed, yet those exposed to Bd still experienced growth limitations. Conversely, Northern Leopard Frogs consumed the same quantity of food no matter their exposure status, but refugia presence had an effect on feeding. These results suggest that sublethal effects of disease can have ecologically relevant impacts in amphibians that can result in reduced size, likely because of high metabolic costs of disease response. Size is both a predictor of time to reproduction and fecundity, and reductions in individual growth may have important consequences for populations.

Encouraging news for in situ conservation: Translocation of salamander larvae has limited impacts on their skin microbiota.

The key role of symbiotic skin bacteria communities in amphibian resistance to emerging pathogens is well recognized, but factors leading to their dysbiosis are not fully understood. In particular, the potential effects of population translocations on the composition and diversity of hosts' skin microbiota have received little attention, although such transfers are widely carried out as a strategy for amphibian conservation. To characterize the potential reorganization of the microbiota over such a sudden environmental change, we conducted a common-garden experiment simulating reciprocal translocations of yellow-spotted salamander larvae across three lakes. We sequenced skin microbiota samples collected before and 15 days after the transfer. Using a database of antifungal isolates, we identified symbionts with known function against the pathogen Batrachochytrium dendrobatidis, a major driver of amphibian declines. Our results indicate an important reorganization of bacterial assemblages throughout ontogeny, with strong changes in composition, diversity and structure of the skin microbiota in both control and translocated individuals over the 15 days of monitoring. Unexpectedly, the diversity and community structure of the microbiota were not significantly affected by the translocation event, thus suggesting a strong resilience of skin bacterial communities to environmental change-at least across the time-window studied here. A few phylotypes were more abundant in the microbiota of translocated larvae, but no differences were found among pathogen-inhibiting symbionts. Taken together, our results support amphibian translocations as a promising strategy for this endangered animal class, with limited impact on their skin microbiota.

Continent-wide recent emergence of a global pathogen in African amphibians

IntroductionEmerging infectious diseases are increasingly recognized as a global threat to wildlife. Pandemics in amphibians, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), have resulted in biodiversity loss at a global scale. Genomic data suggest a complex evolutionary history of Bd lineages that vary in pathogenicity. Africa harbors a significant proportion of global amphibian biodiversity, and multiple Bd lineages are known to occur there; yet, despite the decline of many host species, there are currently no described Bd-epizootics. Here, we describe the historical and recent biogeographical spread of Bd and assess its risk to amphibians across the continent of Africa.MethodsWe provide a 165-year view of host-pathogen interactions by (i) employing a Bd assay to test 4,623 specimens (collected 1908–2013); (ii) compiling 12,297 published Bd records (collected 1852–2017); (iii) comparing the frequency of Bd-infected amphibians through time by both country and region; (iv) genotyping Bd lineages; (v) histologically identifying evidence of chytridiomycosis, and (vi) using a habitat suitability model to assess future Bd risk.ResultsWe found a pattern of Bd emergence beginning largely at the turn of the century. From 1852–1999, we found low Bd prevalence (3.2% overall) and limited geographic spread, but after 2000 we documented a sharp increase in prevalence (18.7% overall), wider geographic spread, and multiple Bd lineages that may be responsible for emergence in different regions. We found that Bd risk to amphibians was highest in much of eastern, central, and western Africa.DiscussionOur study documents a largely overlooked yet significant increase in a fungal pathogen that could pose a threat to amphibians across an entire continent. We emphasize the need to bridge historical and contemporary datasets to better describe and predict host-pathogen dynamics over larger temporal scales.

Host immune responses to enzootic and invasive pathogen lineages vary in magnitude, timing, and efficacy.

Infectious diseases of wildlife continue to pose a threat to biodiversity worldwide, yet pathogens are far from uniform in virulence or host disease outcome. Within the same pathogen species, virulence can vary considerably depending on strain or lineage, in turn eliciting variable host responses. One pathogen that has caused extensive biodiversity loss is the amphibian-killing fungus, Batrachochytrium dendrobatidis (Bd), which is comprised of a globally widespread hypervirulent lineage (Bd-GPL), and multiple geographically restricted, enzootic lineages. Whereas host immunogenomic responses to Bd-GPL have been characterized in a number of amphibian species, immunogenomic responses to geographically restricted, enzootic Bd lineages are less clear. To examine lineage-specific host immune responses to Bd, we exposed a species of pumpkin toadlet, Brachycephalus pitanga, which is endemic to Brazil's Southern Atlantic Forest, to either the Bd-GPL or the enzootic Bd-Asia-2/Brazil (hereafter Bd-Brazil) lineage. Using temporal samples from early, mid, and late infection stages, we quantified functional immunogenomic responses over the course of infection using differential gene expression tests and coexpression network analyses. Host immune responses varied significantly with Bd lineage. Relative to controls, toadlet responses to Bd-Brazil were weak at early infection (25 genes significantly differentially expressed), peaked by mid-stage infection (414 genes), and were nearly fully resolved by late-stage infection (nine genes). In contrast, responses to Bd-GPL were magnified and delayed; toadlets significantly differentially expressed 111 genes early, 87 genes at mid-stage infection, and 726 genes by late-stage infection relative to controls. Given that infection intensity did not vary between mid- and late-stage disease in either Bd-Brazil or Bd-GPL treatments, this suggests that pumpkin toadlets may be at least partially tolerant to the enzootic Bd-Brazil lineage. In contrast, late-stage immune activation against Bd-GPL was consistent with immune dysregulation previously observed in other species. Our results demonstrate that both the timing of immune response and the particular immune pathways activated are specific to Bd lineage. Within regions where multiple Bd lineages co-occur, and given continued global Bd movement, these differential host responses may influence not only individual disease outcome, but transmission dynamics at the population and community levels.

Water Pollution Increases the Risk of Chytridiomycosis in Mexican Amphibians

Chytridiomycosis is affecting amphibians worldwide, causing the decline and extinction of several amphibian populations. The disease is caused by the fungus Batrachochytrium dendrobatidis (Bd), a multihost pathogen living in freshwater habitats. While several environmental factors have been associated with the prevalence of Bd and its virulence, the effects of water quality on the pathogen are not clear yet. Some evidence suggests that water pollution may reduce amphibians' immune response and increase prevalence of Bd. To explore this hypothesis, we analyzed the relationship between water quality and the presence of Bd by using spatial data mining of 150 geolocations of Bd in amphibians from 9 families where Bd positive specimens have been previously reported, and water quality in 4,202 lentic and lotic water bodies in Mexico from 2010 to 2021. Our model showed that in the 3 main families where Bd was recorded, its presence is high in locations with low water quality, i.e., water polluted likely contaminated with urban and industrial waste. Using this model, we inferred areas suitable for Bd in Mexico; mainly in poorly studied areas along the gulf and on the pacific slope. We further argue that actions to reduce water pollution should become an integral part of public policies to prevent the spread of Bd and protect amphibians from this deadly pathogen.

The effect of salt dosing for chytrid mitigation on tadpoles of a threatened frog, Litoria aurea

The novel fungal pathogen Batrachochytrium dendrobatidis (chytrid) is one of the greatest threats to amphibians worldwide. Small increases in water salinity (up to ca. 4 ppt) have been shown to limit chytrid transmission between frogs, potentially providing a way to create environmental refugia to reduce its impact at a landscape scale. However, the effect of increasing water salinity on tadpoles, a life stage confined to water, is highly variable. Increased water salinity can lead to reduced size and altered growth patterns in some species, with flow-on effects to vital rates such as survival and reproduction. It is thus important to assess potential trade-offs caused by increasing salinity as a tool to mitigate chytrid in susceptible frogs. We conducted laboratory experiments to examine the effects of salinity on the survival and development of tadpoles of a threatened frog (Litoria aurea), previously demonstrated as a suitable candidate for trialling landscape manipulations to mitigate chytrid. We exposed tadpoles to salinity ranging from 1 to 6 ppt and measured survival, time to metamorphosis, body mass and locomotor performance of post-metamorphic frogs as a measure of fitness. Survival and time to metamorphosis did not differ between salinity treatments or controls reared in rainwater. Body mass was positively associated with increasing salinity in the first 14 days. Juvenile frogs from three salinity treatments also showed the same or better locomotor performance compared to rainwater controls, confirming that environmental salinity may influence life history traits in the larval stage, potentially as a hormetic response. Our research suggests that salt concentrations in the range previously shown to improve survival of frogs in the presence of chytrid are unlikely to impact larval development of our candidate threatened species. Our study lends support to the idea of manipulating salinity to create environmental refugia from chytrid for at least some salt-tolerant species.

Strong restructuration of skin microbiota during captivity challenges ex-situ conservation of amphibians.

In response to the current worldwide amphibian extinction crisis, conservation instances have encouraged the establishment of ex-situ collections for endangered species. The resulting assurance populations are managed under strict biosecure protocols, often involving artificial cycles of temperature and humidity to induce active and overwintering phases, which likely affect the bacterial symbionts living on the amphibian skin. However, the skin microbiota is an important first line of defense against pathogens that can cause amphibian declines, such as the chytrid Batrachochytrium dendrobatidis (Bd). Determining whether current husbandry practices for assurance populations might deplete amphibians from their symbionts is therefore essential to conservation success. Here, we characterize the effect of the transitions from the wild to captivity, and between aquatic and overwintering phases, on the skin microbiota of two newt species. While our results confirm differential selectivity of skin microbiota between species, they underscore that captivity and phase-shifts similarly affect their community structure. More specifically, the translocation ex-situ is associated with rapid impoverishment, decrease in alpha diversity and strong species turnover of bacterial communities. Shifts between active and overwintering phases also cause changes in the diversity and composition of the microbiota, and on the prevalence of Bd-inhibitory phylotypes. Altogether, our results suggest that current husbandry practices strongly restructure the amphibian skin microbiota. Although it remains to be determined whether these changes are reversible or have deleterious effects on their hosts, we discuss methods to limit microbial diversity loss ex-situ and emphasize the importance of integrating bacterial communities to applied amphibian conservation.

Cryptic but direct costs of an epidemic caused by Batrachochytrium dendrobatidis in the endangered Sardinian newt Euproctus platycephalus (Amphibia, Caudata)

Abstract Parasites can directly affect host survival by causing cryptic costs that may occur in species when mortality does not take place or is less evident. Costs can be present in differently life history stages or age cohorts or cause age-dependent effects. Here we investigate the effects of chytridiomycete fungus Batrachochytrium dendrobatidis, (Bd), that causes one of the main infectious diseases implicated in numerous mass mortalities and population declines in the class of Amphibia, including in one of the rarest and most threatened salamander in Europe, the endemic Sardinian brook newt Euproctus platycephalus. This species is known to be infected by Bd since 2006, without evident direct cost or mass mortality events being observed. During 5 years of sampling (2007-2011), we captured 273 newts in the main infected area of the Limbara Mountain in the North of Sardinia, and, through epidemiological and age analyzes, we assess that Bd directly affected juvenile recruitment, and it is related to difficulties in the development of the species, with an impact on the females growth.

Disease state associated with chronic toe lesions in hellbenders may alter anti-chytrid skin defenses

Hellbenders (Cryptobranchus alleganiensis) are large, aquatic salamanders from the eastern United States. Both subspecies, eastern and Ozark hellbenders, have experienced declines resulting in federal listing of Ozark hellbenders. The globally distributed chytrid fungus, Batrachochytrium dendrobatidis (Bd) has been detected in both subspecies, and Batrachochytrium salamandrivorans (Bsal) poses a new threat if introduced into North America. Ozark hellbenders also suffer a high prevalence of toe lesions of unknown etiology, with changes in host immunocompetence hypothesized to contribute. Antimicrobial peptides (AMPs) secreted from dermal granular glands may play a role in hellbender health. We collected skin secretions from free-ranging hellbenders and enriched them for small cationic peptides used for growth inhibition assays against Bd and Bsal. Generalized linear mixed models revealed the presence of active toe lesions as the strongest and only significant predictor of decreased Bd inhibition by skin peptides. We also found skin secretions were more inhibitory of Bsal than Bd. MALDI-TOF mass spectrometry revealed candidate peptides responsible for anti-chytrid activity. Results support the hypothesis that hellbender skin secretions are important for innate immunity against chytrid pathogens, and decreased production or release of skin peptides may be linked to other sub-lethal effects of disease associated with toe lesions.

Together or Alone: Evaluating the Pathogen Inhibition Potential of Bacterial Cocktails against an Amphibian Pathogen.

The amphibian fungal skin disease Batrachochytrium dendrobatidis (Bd) has caused major biodiversity losses globally. Several experimental trials have tested the use of Janthinobacterium lividum to reduce mortality due to Bd infections, usually in single-strain amendments. It is well-characterized in terms of its anti-Bd activity mechanisms. However, there are many other microbes that inhibit Bd in vitro, and not all experiments have demonstrated consistent results with J. lividum. We used a series of in vitro assays involving bacterial coculture with Bd lawns, bacterial growth tests in liquid broth, and Bd grown in bacterial cell-free supernatant (CFS) to determine: (i) which skin bacteria isolated from a locally endangered amphibian, namely, the Colorado boreal toad (Anaxyrus boreas boreas), are able to inhibit Bd growth; (ii) whether multistrain combinations are more effective than single-strains; and (iii) the mechanism behind microbe-microbe interactions. Our results indicate that there are some single strain and multistrain probiotics (especially including strains from Pseudomonas, Chryseobacterium, and Microbacterium) that are potentially more Bd-inhibitive than is J. lividum alone and that some combinations may lead to a loss of inhibition, potentially through antagonistic metabolite effects. Additionally, if J. lividum continues being developed as a wild boreal toad probiotic, we should investigate it in combination with Curvibacter CW54D, as they inhibited Bd additively and grew at a higher rate when combined than did either alone. This highlights the fact that combinations of probiotics function in variable and unpredictable ways as well as the importance of considering the potential for interactions among naturally resident host microbiota and probiotic additions. IMPORTANCE Batrachochytrium dendrobatidis (Bd) is a pathogen that infects amphibians globally and is causing a biodiversity crisis. Our research group studies one of the species affected by Bd, namely, the Colorado boreal toad (Anaxyrus boreas boreas). Many researchers focus their studies on one probiotic bacterial isolate called Janthinobacterium lividum, which slows Bd growth in lab cultures and is currently being field tested in Colorado boreal toads. Although promising, J. lividum is not consistently effective across all amphibian individuals or species. For Colorado boreal toads, we addressed whether there are other bacterial strains that also inhibit Bd (potentially better than does J. lividum) and whether we can create two-strain probiotics that function better than do single-strain probiotics. In addition, we evaluate which types of interactions occur between two-strain combinations and what these results mean in the context of adding a probiotic to an existing amphibian skin microbiome.

Chytridiomycosis and climate change: exposure to Batrachochytrium dendrobatidis and mild winter conditions do not increase mortality in juvenile agile frogs during hibernation

AbstractHibernation is often associated with high mortality, especially during early life stages, and losses can be exacerbated by unusual winter conditions or if animals enter hibernation carrying a disease. Here, we examined how overwintering amphibians may be affected by the combined effects of mild winters, which are projected to increase in frequency due to climate change, and of chytridiomycosis, a disease that has contributed to the decline of hundreds of species worldwide. We exposed juvenile agile frogs Rana dalmatina to Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, and subsequently subjected them to either a long, cold winter (1.5°C for 91 days) or a short, mild winter (4.5°C for 61 days) under laboratory conditions. Agile frogs proved to be highly resistant to Bd as only 37% of Bd‐exposed individuals became infected as determined before hibernation, and prevalence further decreased to 8% by the end of hibernation, with individuals showing very low infection intensity values. We observed lack of mortality in control and Bd‐exposed groups also, in both types of winter. The two types of winter we simulated did not result in differing body mass loss either alone or in combination with experimental infection. In the Bd‐exposed group, the two types of winter also did not cause differences in prevalence and infection intensity. However, among Bd‐exposed frogs, individuals that were Bd negative when entering hibernation lost more body mass than their conspecifics that carried the fungus at the onset of overwintering. Based on our results, warming winter climate conditions, with or without Bd infection, do not decrease body mass and survival rate of hibernating agile frogs, and do not increase susceptibility of individuals to chytridiomycosis. It remains to be seen to what extent the relatively weak effects of milder winters can be generalized to other amphibians of the temperate climate zone.

Pathogen load predicts host functional disruption: A meta‐analysis of an amphibian fungal panzootic

Abstract The progression of infectious disease depends on the intensity of and sensitivity to pathogen infection. Understanding commonalities in trait sensitivity to pathogen infection across studies through meta‐analytic approaches could provide insight to the pathogenesis of infectious diseases. The globally devastating amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), offers a good case system due to the widely available dataset on disruption to functional traits across species. Here, I systematically conducted a phylogenetically controlled meta‐analysis to test how infection intensity affects different functional traits (e.g. behaviour, physiology, morphology, reproduction) and the survival in amphibians infected with Bd. There was a consistent effect of Bd infection on energy metabolism, while traits related to body condition, osmoregulation, and behaviour generally decreased with Bd infection. Skin integrity, hormone levels, and osmoregulation were most sensitive to Bd infection (minimum Bd load ln 2.5 zoospore equivalent), while higher minimum Bd loads were required to influence reproduction (ln 10.6 zoospore equivalent). Mortality differed between life stages, where juvenile mortality was dependent on infection intensity and exposure duration, while adult mortality was dependent on infection intensity only. Importantly, there were strong biases for studies on immune response, body condition and survival, while locomotor capacity, energy metabolism and cardiovascular traits were lacking. The influence of pathogen load on functional disruption can help inform pathogen thresholds before the onset of irreversible damage and mortality. Meta‐analytic approaches can provide quantitative assessment across studies to reveal commonalities, differences and biases of panzootic diseases, especially for understanding the ecological relevance of disease impact. Read the free Plain Language Summary for this article on the Journal blog.