Search

Batrachochytrium dendrobatidis (Bd) is a fungus that causes chytridiomycosis in amphibians. This fungus is an invasive species that has spread all over the world and is causing mass deaths in many areas. Bd has an efficient life cycle which targets suitable hosts and causes disturbances in amphibian osmoregulation and eventually death. It has caused more than 90 presumed extinctions worldwide. However, even though this fungus is commonly found in Sweden, no cases of chytridiomycosis has been found in the wild. This raises the questions i) what factors makes the infection in amphibians more severe and ii) does temperature affect the severity of Bd infection? According to the thermal mismatch hypothesis pathogens should be more efficient at temperatures where the performance gap between the host and pathogen is the widest. We chose the common toad as a study organism since it can be found all over Sweden and is generally considered to be adapted to colder climates. Our aim was to test the thermal mismatch hypothesis and see if the effect of infection differed between different temperatures. Common toad eggs were collected from two ponds in southern Sweden, raised in the laboratory and metamorphosed juvenile toads were reared in three different temperature rooms, either 14℃, 18℃ or 22℃. There they were either infected with Bd or exposed to a sham infection and monitored for 40 days. We show that Bd infection negatively affects growth and survival of common toads in accordance with previous studies. Furthermore, we found that temperature affects the effect of infection and shows patterns of the thermal mismatch hypothesis.

Chytridiomycosis is affecting hundreds of amphibian species worldwide, but while in tropical areas, adult individuals have been the focus of most investigations, the exact role played by infection intensity of breeding adults is not well understood in temperate areas. We conducted mark-recapture-capture surveys during spiny common toad breeding seasons from 2006 to 2018 at the site of the first recorded outbreak of chytridiomycosis in Europe, the Peñalara Massif (Sierra de Guadarrama National Park, central Spain), and collected infection samples and several variables related to the reproductive effort of male individuals. We used general linear mixed models to evaluate the contribution of study variables on the infection loads of adult male toads exhibited at their capturing date. We also analysed the differences on several male characteristics between the pond with the largest breeding population against the rest of the ponds. We found that the duration of time spent in the waterbody and the condition of the host predicted infection loads. Animals of good physical condition, that spent longer in water, have higher infection levels than individuals with the opposite set of traits. The pond supporting the largest breeding population housed smaller male toads and in poorer condition. Our results are consistent with a shift in reproductive strategy in response to infection and potentially a strategy of tolerance, rather than resistance to infection. These findings have applications for disease mitigation and theoretical implications related to the trade-offs made and the evolution of traits in response to the disease.

The level of detail on host communities needed to understand multihost parasite invasions is an unresolved issue in disease ecology. Coarse community metrics that ignore functional differences between hosts, such as 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 modeling, we show that interspecific differences between host species are important for community-wide infection dynamics of the multihost 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 the basic reproduction number, 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 multihost infection dynamics. Host species that exhibit different functional traits, such as susceptibility and infectiousness, may play similar epidemiological roles in the broader community.

[Background] The fungal pathogenBatrachochytrium dendrobatidis (Bd) threatens amphibian biodiversity and ecosystem stability worldwide. Amphibian skin microbial community structure has been linked to the clinical outcome of Bd infections, yet its overall functional importance is poorly understood. [Methods] Microbiome taxonomic and functional profiles were assessed using high-throughput bacterial 16S rRNA and fungal ITS2 gene sequencing, bacterial shotgun metagenomics and skin mucosal metabolomics. We sampled 56 wild midwife toads (Alytes obstetricans) from montane populations exhibiting Bd epizootic or enzootic disease dynamics. In addition, to assess whether disease-specific microbiome profiles were linked to microbe-mediated protection or Bd-induced perturbation, we performed a laboratory Bd challenge experiment whereby 40 young adult A. obstetricans were exposed to Bd or a control sham infection. We measured temporal changes in the microbiome as well as functional profiles of Bd-exposed and control animals at peak infection. [Results] Microbiome community structure and function differed in wild populations based on infection history and in experimental control versus Bd-exposed animals. Bd exposure in the laboratory resulted in dynamic changes in microbiome community structure and functional differences, with infection clearance in all but one infected animal. Sphingobacterium, Stenotrophomonas and an unclassified Commamonadaceae were associated with wild epizootic dynamics and also had reduced abundance in laboratory Bd-exposed animals that cleared infection, indicating a negative association with Bd resistance. This was further supported by microbe-metabolite integration which identified functionally relevant taxa driving disease outcome, of which Sphingobacterium and Bd were most influential in wild epizootic dynamics. The strong correlation between microbial taxonomic community composition and skin metabolome in the laboratory and field is inconsistent with

Chytridiomycosis is an emerging infectious disease that is significantly reducing global amphibian populations. The disease is caused by Batrachochytrium dendrobatidis (Bd), a fungus that lethally modifies amphibian skin. Recent research has suggested that the cutaneous microbiome of individual amphibians may play a role in susceptibility to the pathogen. In this study, twelve cave salamanders (Eurycea lucifuga) were collected. Cutaneous bacteria from each salamander were isolated and identified using Sanger Sequencing. Additionally, a Bd-challenge assay was performed to determine each isolate’s antifungal activity. Results indicated many microbial isolates possessed inhibitory capabilities against Bd, which may contribute to the cave salamander’s lack of population decline due to chytridiomycosis. This research may contribute to an increased understanding of potential defenses against Bd and ultimately to the development of a treatment to mitigate the chytridiomycosis epidemic.

Chytridiomycosis is a life-threatening disease which infects amphibian species worldwide. Chytrid fungi Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans have been found to be the primary causes of chytridiomycosis. In past research, it has been found that the skin microbiome of certain amphibian species could have fungal inhibition properties, reducing the effects of the chytrid fungi. In this study, 15 eastern red-spotted newts (Notophthalmus viridescens) were collected, to determine if cutaneous bacteria of the newts secrete antifungal compounds. Pure cultures of each bacterium morphotype were produced from mass culture plates, with 188 morphotypes being isolated. The antifungal properties of the skin microbiome were obtained through a Bd assay, which was completed to find comparisons of which bacteria inhibited Bd.

Chytridiomycosis is a life-threatening disease which infects amphibian species worldwide. Chytrid fungi Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans have been found to be the primary causes of chytridiomycosis. In past research, it has been found that the skin microbiome of certain amphibian species could have fungal inhibition properties, reducing the effects of the chytrid fungi. In this study, 15 eastern red-spotted newts (Notophthalmus viridescens) were collected, to determine if cutaneous bacteria of the newts secrete antifungal compounds. Pure cultures of each bacterium morphotype were produced from mass culture plates, with 188 morphotypes being isolated. The antifungal properties of the skin microbiome were obtained through a Bd assay, which was completed to find comparisons of which bacteria inhibited Bd.

The intensity of a pathogen infection plays a key role in determining how the host responds to infection. Hosts with high infections are more likely to transmit infection to others, and are may be more likely to experience progression from infection to disease symptoms, to being physiologically compromised by disease. Understanding how and why hosts exhibit variation in infection intensity therefore plays a major part in developing and implementing measures aimed at controlling infection spread, its effects, and its chance of persisting and circulating within a population of hosts. To track the relative importance of a number of variables in determining the level of infection intensity, we ran field-surveys at two breeding sites over a 12 month period using marked larvae of the common midwife toad (Alyes obstetricans) and their levels of infection with the amphibian pathogen Batrachochytrium dendrobatidis (Bd). At each sampling occasion we measured the density of larvae, the temperature of the water in the 48 h prior to sampling, the period of time the sampled individual had been in the water body, the developmental (Gosner) stage and the intensity of Bd infection of the individual. Overall our data suggest that the temperature and the duration of time spent in the water play a major role in determining the intensity of Bd infection within an individual host. However, although the duration of time spent in the water was clearly associated with infection intensity, the relationship was negative: larvae that had spent less than 3–6 months in the water had significantly higher infection intensities than those that had spent over 12 months, although this infection intensity peaked between 9 and 12 months. This could be due to animals with heavier infections developing more quickly, suffering increased mortality or, more likely, losing their mouthparts (the only part of anuran larvae that can be infected with Bd). Overall, our results identify drivers of infection intens

Amphibians are threatened globally and emerging diseases are some of the most important drivers of their catastrophic situation. There is increasing evidence that the international trade in live amphibians is one of the most important mechanisms driving pathogen pollution. Here, we report the presence of Batrachochytrium dendrobatidis (Bd) and Ranavirus in 11% of tested individuals in legal amphibian trade fairs in Spain. Although none of the Bd infected animals in trade fairs presented disease symptoms, symptoms of ranavirosis were observed in some specimens, which were nonetheless still offered for sale. None of the traders who were selling infected animals showed interest in engaging in collaboration to control infections when offered for free. In addition, a large private urodele collection confiscated by the police in Barcelona comprised a number of illegally wild-caught species. Many confiscated individuals presented signs of poor welfare and several were positive for Bd. Our results indicate the urgent need for implementation of real sanitary regulations or effective legislation governing the practice of trade in living amphibians to prevent pathogen spread in Europe.

We report the first cases of mortality in anurans associated with the presence of the fungus Batrachochytrium dendrobatidis at four different localities from Catalonia (NE Iberian Peninsula, Spain). All cases were confirmed by both molecular techniques and histology. The infected individuals were two Mediterranean painted frogs (Discoglossus pictus) from Girona province found in 2018 and 2020, one Iberian waterfrog (Pelophylax perezi) from Tarragona province found in 2018, and one European common frog (Rana temporaria) from Barcelona province found in 2019. This is the first time that mortality associated with this pathogen has been confirmed in D. pictus and P. perezi. The role of the fungus as an agent possibly leading to death, in association with other external environmental factors, is discussed. These findings could suggest a recent increase of the incidence of this disease in the region. Some of these cases are particularly worrying because of their occurrence close to sites where some endemic amphibian species with extremely reduced distributions inhabit.

[Resumen] Las enfermedades emergentes, como la quitridiomicosis y la ranavirosis, están mermando a las poblaciones de anfibios en España y en otras regiones del mundo. En la península ibérica, Alytes obstetricans ha sido una de las especies más perjudicadas por las epizootias. La quitridiomicosis es una enfermedad infecciosa provocada por algunos hongo quítridos como Batrachochytrium dendrobatidis. Este hongo ataca a la piel de los anfibios adultos, provocando la muerte en el peor de los casos. La persistencia de Bd en al ambiente es alta y la susceptabilidad de sus huéspedes depende en cierta medida de factores tanto bióticos como abióticos. Para frenar el progeso de estas enfermedades y el declive de los anfibios, algunos gobiernos y organizaciones internacionales han comenzado a tomar ciertas medidas. Sin embargo, todavía se necesita seguir legislando e investigando., [Resumo] As enfermidades emerxentes, como a quitridiomicose ou a ranavirose, están a esgotar as poboacións de anfibios en España e noutras rexións do mundo. Na península ibérica, Alytes obstetricans foi unha das especies máis afectadas polas epizootias. A quitridiomicose é unha enfermidade infecciosa causada por algúns fungos quítridos como o Batrachochytrium dendrobatidis. Este fungo ataca á pel dos anfibios adultos, causando a morte no peor dos casos. A persistencia de Bd no ambiente é elevada e a susceptibilidade dos seus hóspedes depende en certa medida de factores bióticos e abióticos. Para frear a propagación destas enfermidades e o declive dos anfibios, algúns gobernos e organizacións internacionais comezaron a tomar certas medidas. Non obstante, aínda é necesario seguir lexislando e investigando., [Abstract] Emerging diseases, such as chytridiomycosis and ranavirus, are depleting amphibian populations in Spain and other regions of the world. In the iberian peninsula, Alytes obstetricans has been one of the most affected species by epizootics. Chytridiomycosis is an infectious disease caused by some chytrid fungi such as Batrachochytrium dendrobatidis. This fungus attacks the skin of adult amphibians, causing death in the worst cases. The persistence of Bd in the environment is high and the susceptibility of its hosts depends to some extent on both biotic and abiotic factors. To brake the spread of these diseases and the decline of amphibians, some governments and international organizations have begun to take certain measures. However, further legislation and research is still needed.

Amphibians are globally among the most endangered taxonomic groups of vertebrates. This is partly due to the chytrid fungus Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis, that have led to eradication of more than 90 species of amphibians worldwide. The spadefoot toad (Pelobates fuscus) is one of the Swedish red listed species (VU) that are at risk of being affected by Bd. The species is currently in the National Action Program for Endangered Species which is a step along the way to achieving the Environmental Quality Objectives. However, even though a lot of effort has been put into improving the circumstances for the spadefoot toad by the Swedish County Administrative Boards, the population has undergone a downward trend. Therefore, the purpose of this field study was to investigate possible reasons which was accomplished by performing an inventory of spadefoot toads as well as examining environmental factors in terms of pH and conductivity in Frihult, Scania County. It turned out to be a significant decline of spadefoot toad from 2010 to 2020 while other anurans in the area have been increasing. Meanwhile, there was no change in either pH or conductivity. After taking multiple aspects into consideration, including previously performed eDNA analyses, is it consequently reasonable to assume that chytridiomycosis has had an impact regarding the decline., Chytridiomykos - groddjurens pandemi COVID-19 tog världen med storm. För groddjuren har detta länge varit vardag. Risken att plötsligt drabbas av hudavfall, kramper, och till slut bli förlamad och invänta döden är att räkna med för de som smittats av sjukdomen. Detta är chytridiomykos. Chytridiomykos orsakas av en vattenburen parasitisk svamp som ofarlig för människor, men har utrotat grodor på ett sätt som aldrig tidigare skådats i någon djurgrupp i mänsklighetens historia. Sedan 70-talet har den spridit sig från östra Asien över hela världen och utplånat minst 90 arter och åsamkat ytterligare massdöd och populationsminskningar hos över 700 arter. I Sverige upptäcktes närvaron av sjukdomen 2010. Även om det hittills inte har dokumenterats några dödsfall ledde rädslan för dess möjliga ödesdigra konsekvenser till att detta behövde studeras närmare. Lökgrodan är en av våra redan utrotnings- hotade svenska grodor som riskerar att råka illa ut av chytridiomykos. Arten är exklusiv för Skåne och befinner sig enbart på ett fåtal områden. Ett av dessa områden är Frihult, “Skånes eldorado för grodor”, där Länsstyrelsen gjort många insatser för att optimera omständigheterna för just lökgrodan. Trots detta har beståndet haft en nedåtgående utvecklingsriktning de senaste åren. För att få en bättre överblick av situationen genomfördes en inventering av grodor i Frihult där årets resultat jämfördes med tiden innan sjukdomen fanns i området. Även vattnets kemi undersöktes för att avgöra om det skulle kunna vara anledningen till en potentiell förändring. Det visade sig att lökgrodan har minskat signifikant, både i antal individer och i antal vattenområden. Samtidigt har vattenkemin inte förändrats, och det gick därmed att utesluta att vattenkemin haft något med lökgrodans negativa utveckling att göra. De andra grodarterna har dock ökat drastiskt, vilket tyder på att dessa antingen inte är lika påverkade av orsaken till nedgången alternativt är orsaken till nedgången. Eftersom dessa

The recent introduction of the chytrid fungus Batrachochytrium salamandrivorans into north-eastern Spain threatens salamander diversity on the Iberian Peninsula. We assessed the current epidemiological situation with extensive field sampling of urodele populations. We then sought to delineate priority regions and identify conservation units for the Iberian Peninsula by estimating the susceptibility of Iberian urodeles using laboratory experiments, evidence from mortality events in nature and captivity and inference from phylogeny. None of the 1395 field samples, collected between 2015 and 2021 were positive for Bsal and no Bsal-associated mortality events were recorded, in contrast to the confirmed occurrence of Bsal outbreak previously described in 2018. We classified five of eleven Iberian urodele species as highly susceptible, predicting elevated mortality and population declines following potential Bsal emergence in the wild, five species as intermediately susceptible with variable disease outcomes and one species as resistant to disease and mortality. We identified the six conservation units (i.e., species or lineages within species) at highest risk and propose priority areas for active disease surveillance and field biosecurity measures. The magnitude of the disease threat identified here emphasizes the need for region-tailored disease abatement plans that couple active disease surveillance to rapid and drastic actions.

Considering that emerging infectious diseases are one of the major drivers of global amphibian decline, controlling the spread of infections are evenmore challenging. Amphibian skin disease chytridiomycosis, which is caused by two species of fungi belonging to the Batrachochytrium genus, has been detected in at least 700 amphibian species causingmass mortalities in all continents where amphibian soccur. Most Alytes species, including the Beticmid wife toad (A. dickhilleni), are highly susceptible to B. dendrobatidis(Bd) with lethal consequences. The presence of Bd infection in A. dickhilleni was confirmed ten years ago in just three localities across the entire distribution range of this threatened species. Here we report the extraordinary Bd expansion through the entire distribution range of A. dickhilleniand analyse if former infected populations acted as the source of transmission events to current infected populations. Currently,Bd infection is broadly distributed across the entire distribution range of the species and the increase of infection prevalence reached 30–50% during a decade. The populations where the infection was detected a decade ago could be identified as likely sources of infection for somelocations where the pathogen is now present. The introduction of infected amphibian hosts into previously naïve A. dickhilleni breeding sites, and otheranthropogenic processes, are seeming to be the most plausible way of Bd range expansion, motivating mass mortalities, population declines and extirpation events of this threatened amphibian species.

As a result of anthropogenic activities, changes to the chemistry of Earth's atmosphere pose a threat to ecosystemhealth and biodiversity. One such change is the increase in tropospheric ozone (O3), which is particularly severeinthe Mediterranean basin area, where the levelsof this pollutant are chronically high during spring and summertime. Within this region, Mediterranean mountain ecosystems are hot spots for biodiversity which may be espe-cially vulnerable to changes in O3levels. Declines in montane amphibian populations have been recorded world-wide, including the Mediterranean basin. A significant driver of these declines is the emerging infection disease,chytridiomycosis, caused by the aquatic fungusBatrachochytrium dendrobatidis(Bd). Chytridiomycosis has neg-atively affected populations of several amphibian species in the Spanish Central Range, including in the SierraGuadarrama, and interactions with other biotic and abiotic factors are an important part of these declines. How-ever, there is little evidence or knowledge of whether tropospheric O3levels may be another factor in the out-breaks of this disease. To test the hypothesis that O3levels are another interactive driver ofBdinfectiondynamics, two different approaches were followed: 1) an experimental study in open top chambers was usedto quantify the aspects of howBdinfection progressed throughout the metamorphic process under four differentO3levels; and 2) afield epidemiological study was used to analyse the relationship between theBdinfection loadin the Sierra de Guadarrama and tropospheric O3levels during a 9 year period. Our results suggest that high O3levels significantly delayed the rate of development of tadpoles and increasedBdinfection, providing empiricalevidence of two new separate ways that may explain population declines of montane amphibians

Chytridiomycosis is a potentially deadly skin disease found in amphibian populations worldwide. The disease is caused by the fungus Batrachochytrium dendrobatidis (Bd) which grows on the skin of amphibians. The fungus can disrupt the homeostatic functions of amphibian skin and can lead to death. An amphibian’s antimicrobial skin secretions, cutaneous microbial communities and the environmental water quality have the potential to influence resistance to Bd infection. However, few studies have examined how these factors interact to impart resistance. Columbia spotted frogs (Lithobates luteiventris) are native to western Montana and can be affected by chytridiomycosis. Three lakes known to be positive for Bd were used as collection sites over the course of the summer of 2018. Each frog was swabbed for bacterial and fungal DNA and the frogs were placed in a solution to collect antimicrobial peptides (AMPs) secreted from the skin. Water samples were collected at each site and analyses were performed to assess various environmental parameters. Early results suggest that AMPs may affect the relative abundance of an important anti-fungal bacteria (Rhizobacter) which influences Bd status. The goal of the ongoing research is to better understand how interactions between skin secretions, cutaneous microbial communities and environmental parameters allow Columbia spotted frogs to resistant chytridiomycosis, and to use this information to better predict and treat future outbreaks.

While epizootics increasingly affect wildlife, it remains poorly understood how the environment shapes most host–pathogen systems. Here, we employ a three‐step framework to study microclimate influence on ectotherm host thermal behaviour, focusing on amphibian chytridiomycosis in fire salamanders (Salamandra salamandra) infected with the fungal pathogen Batrachochytrium salamandrivorans (Bsal). Laboratory trials reveal that innate variation in thermal preference, rather than behavioural fever, can inhibit infection and facilitate salamander recovery under humidity‐saturated conditions. Yet, a 3‐year field study and a mesocosm experiment close to the invasive Bsal range show that microclimate constraints suppress host thermal behaviour favourable to disease control. A final mechanistic model, that estimates range‐wide, year‐round host body temperature relative to microclimate, suggests that these constraints are rule rather than exception. Our results demonstrate how innate host defences against epizootics may remain constrained in the wild, which predisposes to range‐wide disease outbreaks and population declines.

Chytridiomycosis is a potentially deadly skin disease found in amphibian populations worldwide. The disease is caused by the fungus Batrachochytrium dendrobatidis (Bd) which grows on the skin of amphibians. The fungus can disrupt the homeostatic functions of amphibian skin and can lead to death. An amphibian’s antimicrobial skin secretions, cutaneous microbial communities and the environmental water quality have the potential to influence resistance to Bd infection. However, few studies have examined how these factors interact to impart resistance. Columbia spotted frogs (Lithobates luteiventris) are native to western Montana and can be affected by chytridiomycosis. Three lakes known to be positive for Bd were used as collection sites over the course of the summer of 2018. Each frog was swabbed for bacterial and fungal DNA and the frogs were placed in a solution to collect antimicrobial peptides (AMPs) secreted from the skin. Water samples were collected at each site and analyses were performed to assess various environmental parameters. Early results suggest that AMPs may affect the relative abundance of an important anti-fungal bacteria (Rhizobacter) which influences Bd status. The goal of the ongoing research is to better understand how interactions between skin secretions, cutaneous microbial communities and environmental parameters allow Columbia spotted frogs to resistant chytridiomycosis, and to use this information to better predict and treat future outbreaks.

Chytridiomycosis is a potentially deadly skin disease found in amphibian populations worldwide. The disease is caused by the fungus Batrachochytrium dendrobatidis (Bd) which grows on the skin of amphibians. The fungus can disrupt the homeostatic functions of amphibian skin and can lead to death. An amphibian’s antimicrobial skin secretions, cutaneous microbial communities and the environmental water quality have the potential to influence resistance to Bd infection. However, few studies have examined how these factors interact to impart resistance. Columbia spotted frogs (Lithobates luteiventris) are native to western Montana and can be affected by chytridiomycosis. Three lakes known to be positive for Bd were used as collection sites over the course of the summer of 2018. Each frog was swabbed for bacterial and fungal DNA and the frogs were placed in a solution to collect antimicrobial peptides (AMPs) secreted from the skin. Water samples were collected at each site and analyses were performed to assess various environmental parameters. Early results suggest that AMPs may affect the relative abundance of an important anti-fungal bacteria (Rhizobacter) which influences Bd status. The goal of the ongoing research is to better understand how interactions between skin secretions, cutaneous microbial communities and environmental parameters allow Columbia spotted frogs to resistant chytridiomycosis, and to use this information to better predict and treat future outbreaks.

Chytridiomycosis is a potentially deadly skin disease found in amphibian populations worldwide. The disease is caused by the fungus Batrachochytrium dendrobatidis (Bd) which grows on the skin of amphibians. The fungus can disrupt the homeostatic functions of amphibian skin and can lead to death. An amphibian’s antimicrobial skin secretions, cutaneous microbial communities and the environmental water quality have the potential to influence resistance to Bd infection. However, few studies have examined how these factors interact to impart resistance. Columbia spotted frogs (Lithobates luteiventris) are native to western Montana and can be affected by chytridiomycosis. Three lakes known to be positive for Bd were used as collection sites over the course of the summer of 2018. Each frog was swabbed for bacterial and fungal DNA and the frogs were placed in a solution to collect antimicrobial peptides (AMPs) secreted from the skin. Water samples were collected at each site and analyses were performed to assess various environmental parameters. Early results suggest that AMPs may affect the relative abundance of an important anti-fungal bacteria (Rhizobacter) which influences Bd status. The goal of the ongoing research is to better understand how interactions between skin secretions, cutaneous microbial communities and environmental parameters allow Columbia spotted frogs to resistant chytridiomycosis, and to use this information to better predict and treat future outbreaks.

The chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused worldwide declines in amphibian populations. While Bd is widespread in southern and central Europe, its occurrence and distribution in northernmost Europe is mostly unknown. We surveyed for Bd in breeding anurans in Sweden by sampling 1917 amphibians from 101 localities and 3 regions in Sweden (southern, northern and central). We found that Bd was widespread in southern and central Sweden, occurring in all 9 investigated species and in 45.5% of the 101 localities with an overall prevalence of 13.8%. No infected individuals were found in the 4 northern sites sampled. The records from central Sweden represent the northernmost records of Bd in Europe. While the proportion of sites positive for Bd was similar between the southern and central regions, prevalence was much higher in the southern region. This was because southern species with a distribution mainly restricted to southernmost Sweden had a higher prevalence than widespread generalist species. The nationally red-listed green toad Bufotes variabilis and the fire-bellied toad Bombina bombina had the highest prevalence (61.4 and 48.9%, respectively). Across species, Bd prevalence was strongly positively, correlated with water temperature at the start of egg laying. However, no individuals showing visual signs of chytridiomycosis were found in the field. These results indicate that Bd is widespread and common in southern and central Sweden with southern species, breeding in higher temperatures and with longer breeding periods, having higher prevalence. However, the impact of Bd on amphibian populations in northernmost Europe remains unknown.

The fungal pathogen Batrachochytrium dendrobatidis (Bd) is implicated in global declines of amphibian populations and has been documented in African specimens originally collected as far back as the 1930s. Numerous recent surveys focusing on regional pathogen prevalence have greatly increased the number of known occurrences of Bd in African species, but few studies have focused on continental distribution patterns. We analyzed all known positive occurrences of Bd in African amphibians to date, including newly reported data from Cameroon, the Democratic Republic of the Congo, Gabon, Namibia, and the Republic of the Congo. Records from both Namibia and the Republic of the Congo reported herein represent first positive occurrences for these countries. With this most comprehensive sampling of the African continent to date we identified patterns of Bd-positive occurrences associated with (1) location (i.e., biogeographic region, country), (2) taxonomy, (3) life history, and (4) threat of extinction. We used fine-grained (30 arc seconds) environmental niche models (ENMs) to predict the continental distribution of Bd and identify hotspots for the pathogen, including areas not previously modeled to have high suitability for the fungus, and areas of high amphibian biodiversity from which Bd has not yet been documented. Our ENMs predicted that the environmentally suitable range of Bd encompasses vast areas of high amphibian biodiversity, including the Congo Basin and the Albertine Rift. Although our ENMs indicated that West Africa is environmentally suitable for Bd, the fungus has not been reported west of the Dahomey Gap. Likewise, the ENMs also identified regions across the Congo Basin and coastal Angola that are environmentally suitable for the pathogen but from which Bd has not yet been reported, underscoring a need for Bd surveys in these regions. Although amphibian declines in Africa have not been directly attributed to chytridiomycosis, Bd has been detected in over one

The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), responsible for numerous amphibian declines and extinctions, was previously thought to originate from the African continent. This was based on infected museum specimens from early 20th century South Africa, Cameroon and Uganda. Further research on archived specimens from other continents eventually revealed early 20th century records also in Brazil and Japan. Recent robust analysis of genomic diversity and phylogeny of Bd has shown origin from Asia to be more plausible. This raises the issue that the threat of Bd for African amphibians as a novel pathogen has been underestimated. There are now cases where dramatic amphibian declines in disparate mountains on the continent could be attributed to Bd, and this necessitates an urgent realigning of hypotheses and the research agenda for amphibian conservation on the continent. Notably, hotspots of amphibian host naivety include West Africa where this pathogen has so far not been detected. We discuss research gaps that amphibian conservationists might focus on, notably more genomic sequencing of the BdCAPE (the less virulent) lineage to determine its date of emergence, and assessing the susceptibility of different amphibian species to infection, disease and decline to better prioritize conservation actions

Chytridiomycosis is a potentially deadly skin disease found in amphibian populations worldwide. The disease is caused by the fungus Batrachochytrium dendrobatidis (Bd) which grows on the skin of amphibians. The fungus can disrupt the homeostatic functions of amphibian skin and can lead to death. An amphibian’s antimicrobial skin secretions, cutaneous microbial communities and the environmental water quality have the potential to influence resistance to Bd infection. However, few studies have examined how these factors interact to impart resistance. Columbia spotted frogs (Lithobates luteiventris) are native to western Montana and can be affected by chytridiomycosis. Three lakes known to be positive for Bd were used as collection sites over the course of the summer of 2018. Each frog was swabbed for bacterial and fungal DNA and the frogs were placed in a solution to collect antimicrobial peptides (AMPs) secreted from the skin. Water samples were collected at each site and analyses were performed to assess various environmental parameters. Early results suggest that AMPs may affect the relative abundance of an important anti-fungal bacteria (Rhizobacter) which influences Bd status. The goal of the ongoing research is to better understand how interactions between skin secretions, cutaneous microbial communities and environmental parameters allow Columbia spotted frogs to resistant chytridiomycosis, and to use this information to better predict and treat future outbreaks.

The fungal pathogen Batrachochytrium dendrobatidis (Bd) is implicated in global declines of amphibian populations and has been documented in African specimens originally collected as far back as the 1930s. Numerous recent surveys focusing on regional pathogen prevalence have greatly increased the number of known occurrences of Bd in African species, but few studies have focused on continental distribution patterns. We analyzed all known positive occurrences of Bd in African amphibians to date, including newly reported data from Cameroon, the Democratic Republic of the Congo, Gabon, Namibia, and the Republic of the Congo. Records from both Namibia and the Republic of the Congo reported herein represent first positive occurrences for these countries. With this most comprehensive sampling of the African continent to date we identified patterns of Bd-positive occurrences associated with (1) location (i.e., biogeographic region, country), (2) taxonomy, (3) life history, and (4) threat of extinction. We used fine-grained (30 arc seconds) environmental niche models (ENMs) to predict the continental distribution of Bd and identify hotspots for the pathogen, including areas not previously modeled to have high suitability for the fungus, and areas of high amphibian biodiversity from which Bd has not yet been documented. Our ENMs predicted that the environmentally suitable range of Bd encompasses vast areas of high amphibian biodiversity, including the Congo Basin and the Albertine Rift. Although our ENMs indicated that West Africa is environmentally suitable for Bd, the fungus has not been reported west of the Dahomey Gap. Likewise, the ENMs also identified regions across the Congo Basin and coastal Angola that are environmentally suitable for the pathogen but from which Bd has not yet been reported, underscoring a need for Bd surveys in these regions. Although amphibian declines in Africa have not been directly attributed to chytridiomycosis, Bd has been detected in over one

The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), responsible for numerous amphibian declines and extinctions, was previously thought to originate from the African continent. This was based on infected museum specimens from early 20th century South Africa, Cameroon and Uganda. Further research on archived specimens from other continents eventually revealed early 20th century records also in Brazil and Japan. Recent robust analysis of genomic diversity and phylogeny of Bd has shown origin from Asia to be more plausible. This raises the issue that the threat of Bd for African amphibians as a novel pathogen has been underestimated. There are now cases where dramatic amphibian declines in disparate mountains on the continent could be attributed to Bd, and this necessitates an urgent realigning of hypotheses and the research agenda for amphibian conservation on the continent. Notably, hotspots of amphibian host naivety include West Africa where this pathogen has so far not been detected. We discuss research gaps that amphibian conservationists might focus on, notably more genomic sequencing of the BdCAPE (the less virulent) lineage to determine its date of emergence, and assessing the susceptibility of different amphibian species to infection, disease and decline to better prioritize conservation actions

Amphibians in rural landscapes often utilize various types of artificial constructions originally designed for irrigation, livestock supply, or other purposes (e.g., water tanks or cattle troughs) as breeding sites. These sites potentially function as local refugia; however, their importance for amphibian communities has yet to be widely assessed. Here we evaluate the role of artificial constructions in the persistence of amphibian populations in rural areas of central Spain, focusing on two species of conservation concern: the Common Midwife Toad, Alytes obstetricans (Laurenti 1768), and the Parsley Frog, Pelodytes punctatus (Daudin 1802). We surveyed 130 water bodies at 113 localities in an area of 1,450 km during the breeding season of 2018 and documented the type of breeding site, species abundance, amphibian community structure, and any detectable threats. We found non-random patterns of breeding site selection and amphibian species co-occurrence in which A. obstetricans tended to inhabit artificial water tanks with simpler amphibian communities, whereas P. punctatus tended to co-occur in naturalized ponds in abandoned quarries with complex amphibian community structures. We discuss the relevance of artificial breeding sites for the resilience of amphibian populations and propose conservation measures to improve their efficiency in the face of detected threats, including trap effects, alien species, and chytridiomycosis.

The evolutionary history and dispersal pattern of Batrachochytrium dendrobatidis (Bd), an emergent fungal pathogen responsible for the decline and extinctions of many species of amphibians worldwide, is still not well understood. In South America, the tropical Andes are known as an important site for amphibian diversification, but also for being a place where hosts are at greater risk of chytridiomycosis. In an attempt to understand the history and the geographic pattern of Bd-associated amphibian declines in Bolivia, we isolated Bd from hosts at two locations that differ in their chronology of Bd prevalence and host survival outcome, the cloud forests of the Amazonian slopes of the Andes and Lake Titicaca in the altiplano. We genotyped Bd from both locations and sequenced the genome from the cloud forest isolate and then compared them to reference sequences of other Bd strains across the world. We found that the Bolivian chytrid isolates were nearly genotypically identical and that they belong to the global panzootic lineage (Bd-GPL). The Bolivian Bd strain grouped with other tropical New World strains but was closest to those from the Brazilian Atlantic Forest. Our results extend the presence of Bd-GPL to the central Andes in South America and report this hypervirulent strain at Lago Titicaca, where Bd has been detected since 1863, without evidence of amphibian declines. These findings suggest a more complex evolutionary history for this pathogen in Bolivia and may point to the existence of an old lineage of Bd that has since been extirpated following the arrival of the panzootic Bd-GPL or that the timing of Bd-GPL emergence is earlier than generally acknowledged.

Chytridiomycosis, an emerging infectious disease caused by the fungus Batrachochytrium dendrobatidis (Bd), is causing sharp declines in amphibian populations around the globe. A substantial research effort has been made to study the disease, including treatments against Bd, but most treatments have been applied to captive amphibians only. We report a study aimed at clearing wild populations of the Common Midwife toad Alytes obstetricans. We removed all larvae from natural breeding sites (cattle troughs) and conducted two types of severe breeding habitat manipulation (complete drying and fencing for the whole breeding season). While larval removal followed by drying was a successful method of Bd elimination, the effect was only temporary. Since terrestrial habits of adult A. obstetricans prevent them from infection, our findings suggest that, even in simple breeding habitats where all aquatic amphibian stages can be handled and extreme habitat intervention is possible, Bd cannot be eliminated without controlling other potential Bd reservoirs in the surroundings of breeding sites.

Emerging infectious diseases are increasingly recognized as a severe threat to wildlife. Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), is considered one of the most important causes for the decline of amphibian populations worldwide. Identifying potential biological reservoirs and characterizing the role they can play in pathogen maintenance is not only important from a scientific point of view, but also relevant from an applied perspective (e.g. disease control strategies), especially when worldwide distributed invasive species are involved. We aimed (1) to analyse the prevalence and infection intensity of Bd in the invasive red swamp crayfish (Procambarus clarkii) across the western Andalusian region in Spain; and (2) to assess whether the presence of crayfish affects the prevalence and infection intensity of Bd in amphibians of Doñana Natural Space (DNS), a localized highly protected area within the Andalusian region. First, we found that infection prevalence in crayfish guts was 1.5% regionally (four out of 267 crayfish were qPCR positive to Bd, all of them belonging to the same Andalusian population); qPCR positives were histologically confirmed by finding zoosporangia of Bd in gastrointestinal walls of the red swamp crayfish. Second, we found a higher prevalence of Bd infection in DNS (19% for crayfish and 28% for amphibians on average), a place with great diversity and abundance of amphibians. Our analyses showed that prevalence of Bd in amphibians was related to the presence of the red swamp crayfish, indicating that this crayfish could be a suitable predictor of Bd infection in co-occurring amphibians. These results suggest that the red swamp crayfish might be a possible reservoir for Bd, representing an additional indirect impact on amphibians, a role that had not been previously recognised in its invasive range.

[EN] The infectious chytrid fungus Batrachochytrium salamandrivorans (Bsal) has been responsible for severe population declines of salamander populations in Europe. Serious population declines and loss of urodelan diversity may occur if appropriate action is not taken to mitigate against the further spread and impact of Bsal. We provide an overview of several potential mitigation methods, and describe their possible advantages and limitations. We conclude that long-term, context-dependent, multi-faceted approaches are needed to successfully mitigate adverse effects of Bsal, and that these approaches should be initiated pre-arrival of the pathogen. The establishment of ex situ assurance colonies, or management units, for species threatened with extinction, should be considered as soon as possible. While ex situ conservation and preventive measures aimed at improving biosecurity by limiting amphibian trade may be implemented quickly, major challenges that lie ahead are in designing in situ disease containment and mitigation post-arrival and in increasing public awareness.

Emergent infectious diseases are a major driver of the accelerated rates of biodiversity loss that are being documented around the world. Global losses of amphibians provide evidence of this, especially those associated with chytridiomycosis, a lethal skin disease caused by the fungus Batrachochytrium dendrobatidis (Bd). Amphibian skin can harbor diverse bacterial communities that, in some cases, can inhibit the growth of Bd. Thus, there is interest in using skin bacteria as probiotics to mitigate Bd infections in amphibians. However, experiments testing this conservation approach have yielded mixed results, suggesting a lack of understanding about the ecology of these microbial communities. My dissertation research aimed to assess basic ecological questions in microbial ecology and to contribute to the development of probiotics using amphibian skin bacteria. First, to assess whether environmental conditions influence the function of amphibian skin bacterial communities, I conducted a field survey across low and high elevation populations of an amphibian host to assess their skin bacterial communities and metabolite profiles. I found that similar bacterial communities produced different metabolites at different locations, implying a potential functional plasticity. Second, since culturing is critical for characterizing bacteria, I aimed to identify the culture media (low vs high nutrient concentration) that recovers the most representative fraction of the amphibian skin bacterial community. I found that media with low nutrient concentrations cultured a higher diversity and recovered a more representative fraction of the diversity occurring on amphibian skin. I also determined that sampling more individuals is critical to maximize culture collections. Third, I assessed the diversity of the amphibian skin fungal community in relation to Bd infection across eight amphibian species. I determined that amphibian species was the most important predictor of fungal diversity

Chytridiomycosis, the disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has devastated global amphibian biodiversity. Nevertheless, some hosts avoid disease after Bd exposure even as others experience near-complete extirpation. It remains unclear whether the amphibian adaptive immune system plays a role in Bd defence. Here, we describe gene expression in two host species-one susceptible to chytridiomycosis and one resistant-following exposure to two Bd isolates that differ in virulence. Susceptible wood frogs (Rana sylvatica) had high infection loads and mortality when exposed to the more virulent Bd isolate but lower infection loads and no fatal disease when exposed to the less virulent isolate. Resistant American bullfrogs (R. catesbeiana) had high survival across treatments and rapidly cleared Bd infection or avoided infection entirely. We found widespread upregulation of adaptive immune genes and downregulation of important metabolic and cellular maintenance components in wood frogs after Bd exposure, whereas American bullfrogs showed little gene expression change and no evidence of an adaptive immune response. Wood frog responses suggest that adaptive immune defences may be ineffective against virulent Bd isolates that can cause rapid physiological dysfunction. By contrast, American bullfrogs exhibited robust resistance to Bd that is likely attributable, at least in part, to their continued upkeep of metabolic and skin integrity pathways as well as greater antimicrobial peptide expression compared to wood frogs, regardless of exposure. Greater understanding of these defences will ultimately help conservationists manage chytridiomycosis.

Amphibian chytridiomycosis, caused by infection with Batrachochytrium dendrobatidis (Bd), is the most devastating vertebrate disease on record. Reservoir hosts are likely to be important in the Bd‐amphibian system because many amphibian species can carry infections without experiencing mortality. However, while a variety of reservoirs have been proposed, few have been empirically demonstrated to act as competent reservoir hosts. In this study, we investigate whether the common eastern froglet, Crinia signifera, a non‐declining species that is widespread in eastern Australia, is a reservoir host for Bd infection. We conducted a long‐term, large‐scale field survey to investigate disease dynamics in C. signifera at sites where four sympatric, threatened anuran species have severely declined. We also monitored Bd‐infected C. signifera in the laboratory to determine susceptibility and survivorship. Finally, we assessed population age structure to investigate disease impact in the wild. We found that C. signifera is a competent reservoir host, maintaining high prevalence and infection intensities in the wild and in the laboratory, with no signs of sub‐lethal effects or clinical disease. In the wild, the modal age is 4 years with individuals living up to 6 years, indicating that adults can survive across multiple years despite high infection prevalence and intensity. The occurrence of C. signifera at sites with remnant populations of threatened species likely contributes to ongoing disease impact in declining species decades after the arrival of Bd. The presence of C. signifera at sites where threatened species have become extinct inhibits effective reintroductions, and we recommend avoiding sites with high reservoir host abundance when planning reintroductions.

Batrachochytrium dendrobatidis (Bd) is a fungal pathogen which causes the emerging infectious disease chytridiomycosis. Bd presents low host specificity and threatens amphibians worldwide, thus systematic inventory is the key in order to detect and mitigate the effects of the disease. Extensive data collection was conducted in Hungary in 2009-2015 from fourteen different areas. Combined data – recent field sampling on sixteen taxa and the examination of archived Bombina spp. specimens – from 1360 individuals were analysed with qPCR. Two sentinel taxa, Bombina variegata and the members of the Pelophylax esculentus complex were marked to monitor the occurrence of Bd in two core areas (Bakony Mts and Hortobágy National Park, respectively) of sampling. Climatic variables were also examined in core areas to test their effect on prevalence and infection intensity. Among the sixteen sampled amphibian taxa seven tested positive for Bd and the overall prevalence in Hungary was 7.46%. Among the ethanol-fixed Bombina spp. individuals Bd was not detected. In the first core area (Bakony Mts) the overall prevalence in B. variegata was 10.32% and juvenile individuals showed significantly higher prevalence than adults. On the other hand there was a significant negative relationship between infection prevalence and monthly mean air temperature. Finally, in the other core area (Hortobágy National Park) the overall prevalence in P. esculentus complex was 13.00%, and no differences were found in prevalence or infection intensity between sexes, sampling years or age classes.

The emerging infectious disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis, is a major driver pushing many amphibian species to the brink of extinction. Substantial efforts to develop effective protocols that use antifungal drugs have had notable success. Here, we used the antifungal agents itraconazole and thiophanate-methyl, singly and in combination, in an attempt to treat common midwife toad Alytes obstetricans larvae naturally infected with the globalized hypervirulent lineage of B. dendrobatidis. Despite the successful use of itraconazole in a closely related species (A. muletensis), our results show that these antifungal treatments are not always effective and that full clearance of animals cannot be assumed following treatment.

Infectious disease and climate change are considered major threats to biodiversity and act as drivers behind the global amphibian decline. This is, to a large extent, based on short-term studies that are designed to detect the immediate and strongest biodiversity responses to a threatening process. What few long-term studies are available, although typically focused on single species, report outcomes that often diverge significantly from the short-term species responses. Here, we report the results of an 18-year survey of an amphibian community exposed to both climate warming and the emergence of lethal chytridiomycosis. Our study shows that the impacts of infectious disease are ongoing but restricted to two out of nine species that form the community, despite the fact all species can become infected with the fungus. Climate warming appears to be affecting four out of the nine species, but the response of three of these is an increase in abundance. Our study supports a decreasing role of infectious disease on the community, and an increasing and currently positive effect of climate warming. We caution that if the warming trends continue, the net positive effect will turn negative as amphibian breeding habitat becomes unavailable as water bodies dry, a pattern that already may be underway.

Recent outbreaks of chytridiomycosis, the disease of amphibians caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), have contributed to population declines of numerous amphibian species worldwide. The devastating impacts of this disease have led researchers to attempt drastic conservation measures to prevent further extinctions and loss of biodiversity. The conservation measures can be labour-intensive or expensive, and in many cases have been unsuccessful. We developed a mathematical model of Bd outbreaks that includes the effects of demographic stochasticity and within-host fungal load dynamics. We investigated the impacts of one-time treatment conservation strategies during the disease outbreak that occurs following the initial arrival of Bd into a previously uninfected frog population. We found that for all versions of the model, for a large fraction of parameter space, none of the one-time treatment strategies are effective at preventing disease-induced extinction of the amphibian population. Of the strategies considered, treating frogs with antifungal agents to reduce their fungal load had the greatest likelihood of a beneficial outcome and the lowest risk of decreasing the persistence of the frog population, suggesting that this disease mitigation strategy should be prioritized over disinfecting the environment or reducing host density.

The ribosomal gene complex is a multi-copy region that is widely used for phylogenetic analyses of organisms from all 3 domains of life. In fungi, the copy number of the internal transcribed spacer (ITS) is used to detect abundance of pathogens causing diseases such as chytridiomycosis in amphibians and white nose syndrome in bats. Chytridiomycosis is caused by the fungi Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), and is responsible for declines and extinctions of amphibians worldwide. Over a decade ago, a qPCR assay was developed to determine Bd prevalence and pathogen load. Here, we demonstrate the effect that ITS copy number variation in Bd strains can have on the estimation of prevalence and pathogen load. We used data sets from different amphibian species to simulate how ITS copy number affects prevalence and pathogen load. In addition, we tested 2 methods (gBlocks® synthetic standards and digital PCR) to determine ITS copy number in Bd strains. Our results show that assumptions about the ITS copy number can lead to under-or overestimation of Bd prevalence and pathogen load. The use of synthetic standards replicated previously published estimates of ITS copy number, whereas dPCR resulted in estimates that were consistently lower than previously published estimates. Standardizing methods will assist with comparison across studies and produce reliable estimates of prevalence and pathogen load in the wild, while using the same Bd strain for exposure experiments and zoospore standards in qPCR remains the best method for estimating parameters used in epidemiological studies.

Batrachochytrium dendrobatidis (Bd) causes the disease chytridiomycosis associated with amphibian declines. Response and costs of infection varies greatly between species. Bd can induce a stress response in amphibians resulting in elevated corticosterone (CORT). We exposed Bombina variegata and Hyla arborea tadpoles to Bd+ or Bd-Salamandra salamandra larvae and measured CORT release rates, Bd infection loads, and survival through metamorphosis. Tadpoles of both species exposed to Bd+ larvae had elevated CORT release rates compared to tadpoles exposed to Bd-larvae. Bombina variegata appear less resistant to infection than H. arborea, showing higher Bd loads and more infected individuals. Within species, we did not find differences in cost of infection on survival, however more B. variegata tadpoles reached metamorphosis than H. arborea. The differences in resistance may be species specific, owing to higher immunity defenses with H. arborea having higher overall CORT release rates, and differences in antimicrobial peptides, or to differences in Bd strain or other unexplored mechanisms.

Changes in the timings of seasonality as a result of anthropogenic climate change are predicted to occur over the coming decades. While this is expected to have widespread impacts on the dynamics of infectious disease through environmental forcing, empirical data are lacking. Here, we investigated whether seasonality, specifically the timing of spring ice-thaw, affected susceptibility to infection by the emerging pathogenic fungus Batrachochytrium dendrobatidis (Bd) across a montane community of amphibians that are suffering declines and extirpations as a consequence of this infection. We found a robust temporal association between the timing of the spring thaw and Bd infection in two host species, where we show that an early onset of spring forced high prevalences of infection. A third highly susceptible species (the midwife toad, Alytes obstetricans) maintained a high prevalence of infection independent of time of spring thaw. Our data show that perennially overwintering midwife toad larvae may act as a year-round reservoir of infection with variation in time of spring thaw determining the extent to which infection spills over into sympatric species. We used future temperature projections based on global climate models to demonstrate that the timing of spring thaw in this region will advance markedly by the 2050s, indicating that climate change will further force the severity of infection. Our findings on the effect of annual variability on multi-host infection dynamics show that the community-level impact of fungal infectious disease on biodiversity will need to be re-evaluated in the face of climate change.This article is part of the themed issue ‘Tackling emerging fungal threats to animal health, food security and ecosystem resilience’.

Batrachochytrium dendrobatidis (Bd), a fungal pathogen that causes chytridiomycosis in amphibians, has infected >500 species and caused declines and extinctions in >200 species. Recently, a second deadly fungal pathogen that also causes chytridiomycosis, Batrachochytrium salamandrivorans (Bsal) was discovered. The presence of these lethal pathogens in international trade threatens amphibian diversity. In this dissertation, I use a novel modeling approach to predict disease risk from Bd and/or Bsal to amphibian populations in North America and Asia by incorporating pathogen habitat suitability, host availability, the potential presence of an invasive carrier species, and pathogen invasion history. First I identify Bsal threat to North American salamanders to be greatest in the Southeast US, the West Coast, and highlands of Mexico. I then investigate the compounded risk of Bd and Bsal in North America and find highest relative risk in those same areas and in the Sierra Nevada Mountains and the northern Rocky Mountains. However, when I incorporate the historical context of Bd into the model by treating the eastern US as the native range of Bd, I find invasive Bd risk to be highest in the mountain ranges of the western US and Mexico, which could influence how amphibians in these areas respond to Bsal. I also uncover a pattern that suggests the translocation of the American bullfrog (Rana catesbeiana) to western North America may have facilitated Bd spread. Last, I investigate the threat of Bd in Asia and find that mountain forests in China, Southeast Asia, and the Pacific Islands have the highest relative Bd risk, and the potential presence of R. catesbeiana and amphibian richness may have a strong influence on Bd risk. I also predict that climate change may lead to a 3-23% decrease in total area of Bd risk in Asia by 2070. These findings provide helpful guidance for conservation planning and management by further highlighting the role of R. catesbeiana in Bd spre

Since amphibian declines were first proposed as a global phenomenon over a quarter century ago, the conservation community has made little progress in halting or reversing these trends. The early search for a "smoking gun" was replaced with the expectation that declines are caused by multiple drivers. While field observations and experiments have identified factors leading to increased local extinction risk, evidence for effects of these drivers is lacking at large spatial scales. Here, we use observations of 389 time-series of 83 species and complexes from 61 study areas across North America to test the effects of 4 of the major hypothesized drivers of declines. While we find that local amphibian populations are being lost from metapopulations at an average rate of 3.79% per year, these declines are not related to any particular threat at the continental scale; likewise the effect of each stressor is variable at regional scales. This result - that exposure to threats varies spatially, and populations vary in their response - provides little generality in the development of conservation strategies. Greater emphasis on local solutions to this globally shared phenomenon is needed.

Changes in the timings of seasonality as a result of anthropogenic climate change are predicted to occur over the coming decades. While this is expected to have widespread impacts on the dynamics of infectious disease through environmental forcing, empirical data are lacking. Here, we investigated whether seasonality, specifically the timing of spring ice-thaw, affected susceptibility to infection by the emerging pathogenic fungus Batrachochytrium dendrobatidis (Bd) across a montane community of amphibians that are suffering declines and extirpations as a consequence of this infection. We found a robust temporal association between the timing of the spring thaw and Bd infection in two host species, where we show that an early onset of spring forced high prevalences of infection. A third highly susceptible species (the midwife toad, Alytes obstetricans) maintained a high prevalence of infection independent of time of spring thaw. Our data show that perennially overwintering midwife toad larvae may act as a year-round reservoir of infection with variation in time of spring thaw determining the extent to which infection spills over into sympatric species. We used future temperature projections based on global climate models to demonstrate that the timing of spring thaw in this region will advance markedly by the 2050s, indicating that climate change will further force the severity of infection. Our findings on the effect of annual variability on multi-host infection dynamics show that the community-level impact of fungal infectious disease on biodiversity will need to be re-evaluated in the face of climate change.

Amphibians across the planet face the threat of population decline and extirpation caused by the disease chytridiomycosis. Despite consensus that the fungal pathogens responsible for the disease are conservation issues, strategies to mitigate their impacts in the natural world are, at best, nascent. Reducing risk associated with the movement of amphibians, non-amphibian vectors and other sources of infection remains the first line of defence and a primary objective when mitigating the threat of disease in wildlife. Amphibian-associated chytridiomycete fungi and chytridiomycosis are already widespread, though, and we therefore focus on discussing options for mitigating the threats once disease emergence has occurred in wild amphibian populations. All strategies have shortcomings that need to be overcome before implementation, including stronger efforts towards understanding and addressing ethical and legal considerations. Even if these issues can be dealt with, all currently available approaches, or those under discussion, are unlikely to yield the desired conservation outcome of disease mitigation. The decision process for establishing mitigation strategies requires integrated thinking that assesses disease mitigation options critically and embeds them within more comprehensive strategies for the conservation of amphibian populations, communities and ecosystems.

Recently emerged diseases in natural populations present novel problems for biodiversity conservation. Integrated approaches are needed to better understand disease-related threats, to mitigate these threats, and to assist population recovery. My dissertation research confronts the global amphibian biodiversity crisis. The recently emerged infectious disease chytridiomycosis, caused by the chytrid fungal pathogen Batrachochytrium dendrobatidis (Bd), infects hundreds of species around the world and is a major contributor to amphibian population declines. I use a multi-faceted approach to address critical issues of disease-caused amphibian declines. In this dissertation, I implement a novel methodology to gain insights on variability of host response to Bd (Chapter 2). Next, I analyze the spatial genetic structure of post-decline populations to aid conservation (Chapter 3). Finally, I examine the genetic underpinnings of pathogen attenuation – loss of virulence – using genomic sequencing (Chapter 4).First, I examine differential disease progression and host response in two related species (Chapter 2). Determining how different hosts respond to infection by a widespread pathogen is essential for understanding - and ultimately limiting - the devastating effects of emerging infectious diseases. Previous work demonstrated that susceptibility to chytridiomycosis is variable among species, but the mechanism(s) that underlie the difference between winners and losers remains a mystery. I used an integrative approach to analyze host response to infection in two related toad species that are thought to differ in susceptibility: the invasive Cane Toad (Bufo marinus) and the threatened Boreal Toad (Bufo boreas). With my results, I characterize the nature of differential susceptibility and compare host response using genome-wide gene expression analysis. The susceptible B. boreas exhibited high pathogen loads, loss in body weight, severe changes in the epidermis, and dramatic tran

Emerging infectious diseasespose a significant threat to global health, but predicting disease outcomes for particular species can be complicated when pathogen virulence varies across space, time, or hosts. The pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused worldwide declines in frog populations. Not only do Bd isolates from wild populations vary in virulence, but virulence shifts can occur over short timescales when Bd is maintained in the laboratory. We leveraged changes in Bd virulence over multiple generations of passage to better understand mechanisms of pathogen virulence. We conducted whole-genome resequencing of two samples of the same Bd isolate, differing only in passage history, to identify genomic processes associated with virulence attenuation. The isolate with shorter passage history (and greater virulence) had greater chromosome copy numbers than the isolate maintained in culture for longer, suggesting that virulence attenuation may be associated with loss of chromosome copies. Our results suggest that genomic processes proposed as mechanisms for rapid evolution in Bd are correlated with virulence attenuation in laboratory culture within a single lineage of Bd. Moreover, these genomic processes can occur over extremely short timescales. On a practical level, our results underscore the importance of immediately cryo-archiving new Bd isolates and using fresh isolates, rather than samples cultured in the laboratory for long periods, for laboratory infection experiments. Finally, when attempting to predict disease outcomes for this ecologically important pathogen, it is critical to consider existing variation in virulence among isolates and the potential for shifts in virulence over short timescales.