Relationship between environmental, ecological and genetic drivers of emergence in amphibian chytridiomycosis.
Lead Research Organisation:
Imperial College London
Department Name: School of Public Health
Abstract
Of the animal groups for which comprehensive assessments have been made, amphibians rank as the most threatened major taxon, with nearly three times as many amphibian species threatened with extinction as bird species. Disease has been identified as one of the major contributors to amphibian declines and extinctions, with one pathogen singled out as the most dangerous amphibian disease identified to date. Batrachochytrium dendrobatidis, a chytridiomycete fungus, has been implicated in mass mortality events, population declines and species extinctions around the globe. The Amphibian Conservation Summit recently organized by the IUCN recognized that the current state of knowledge regarding this fungus is manifestly inadequate. In response to this research gap, the Summit produced a Declaration calling for immediate research to determine the distribution of the disease, how this distribution was achieved and the consequences of invasion of the pathogen for local amphibian communities. Funded by NERC, we have completed three years of monitoring B. dendrobatidis and chytridiomycosis across Europe and have shown for the first time that infection is widespread, is present in the wild in the UK, and is unfortunately present in the Mallorcan midwife toad, one of the most critically endangered species of amphibian. We now need to add to our current descriptions of the prevalence of infection and test hypotheses generated by these patterns in order to ascertain the processes by which B. dendrobatidis causes populations to collapse. We will do this by using a combination of field surveys and laboratory experiments in order to understand how the dynamics of infection in natural populations lead to extinction. Firstly, we will intensively survey five focal study sites where the disease is present, but is causing different effects in the amphibian populations. We will sample these communities over three years in order to track how infection moves through the various species, and how infection differentially affects larval (tadpole), metamorph and adult stages within a community of amphibians. Using our newly developed environmental molecular assay, we are now able to test the density of infectious stages in the environment. This gives us the ability to directly measure the exposure-levels of amphibians and to assess whether the fungus can persist in the environment in the absence of its host. The idea that there are multiple reservoirs of infection is very important, as extinction is more likely in susceptible species when pathogen 'spillover' occurs from disease reservoirs. We will therefore test these ideas in laboratory and mesocosm systems where we are able to manipulate the density and type of potential reservoirs of B. dendrobatidis. Results from our first NERC grant have shown that there is strong evidence that the international trade in amphibians (specifically Xenopus and North American bullfrogs) is causing multiple introductions of B. dendrobatidis into the UK and mainland Europe. We need to know whether there is variation between these different strains of the pathogen in their ability to cause disease, and to test this idea we will perform challenge experiments in our model species, the common toad Bufo bufo. Once these comparisons have been completed, we will develop mathematical epidemiological models with the explicit goal of predicting the dynamics of disease emergence across several scales. We have strong evidence that temperature is a key determinant of chytrid-driven mortality, and we will develop statistical models to determine the potential effects of global-warming on the distribution of the disease within Europe. Our aim is that these short and long term research goals will eventually enable us to control fungal spread or manage amphibian populations in order to prevent the population declines that are associated with the emergence of this pathogen.
People |
ORCID iD |
Matthew Fisher (Principal Investigator) |
Publications
Bates KA
(2022)
Microbiome function predicts amphibian chytridiomycosis disease dynamics.
in Microbiome
Bielby J
(2015)
Host species vary in infection probability, sub-lethal effects, and costs of immune response when exposed to an amphibian parasite.
in Scientific reports
Canessa S
(2018)
Decision-making for mitigating wildlife diseases: From theory to practice for an emerging fungal pathogen of amphibians
in Journal of Applied Ecology
Clare FC
(2016)
Climate forcing of an emerging pathogenic fungus across a montane multi-host community.
in Philosophical transactions of the Royal Society of London. Series B, Biological sciences
Doddington BJ
(2013)
Context-dependent amphibian host population response to an invading pathogen.
in Ecology
Doddington BJ
(2013)
Context-dependent amphibian host population response to an invading pathogen.
in Ecology
Farrer RA
(2013)
Chromosomal copy number variation, selection and uneven rates of recombination reveal cryptic genome diversity linked to pathogenicity.
in PLoS genetics
Farrer RA
(2011)
Multiple emergences of genetically diverse amphibian-infecting chytrids include a globalized hypervirulent recombinant lineage.
in Proceedings of the National Academy of Sciences of the United States of America
Fernández-Loras A
(2017)
Early exposure to Batrachochytrium dendrobatidis causes profound immunosuppression in amphibians
in European Journal of Wildlife Research
Fisher M
(2009)
Silent Springs: Why Are All the Frogs "Croaking"?
in PLoS Biology
Fisher MC
(2008)
Molecular toolkit unlocks life cycle of the panzootic amphibian pathogen Batrachochytrium dendrobatidis.
in Proceedings of the National Academy of Sciences of the United States of America
Fisher MC
(2018)
Development and worldwide use of non-lethal, and minimal population-level impact, protocols for the isolation of amphibian chytrid fungi.
in Scientific reports
Fisher MC
(2009)
Proteomic and phenotypic profiling of the amphibian pathogen Batrachochytrium dendrobatidis shows that genotype is linked to virulence.
in Molecular ecology
GARNER T
(2011)
Climate change, chytridiomycosis or condition: an experimental test of amphibian survival
in Global Change Biology
Garner TW
(2009)
Using itraconazole to clear Batrachochytrium dendrobatidis infection, and subsequent depigmentation of Alytes muletensis tadpoles.
in Diseases of aquatic organisms
James TY
(2009)
Rapid global expansion of the fungal disease chytridiomycosis into declining and healthy amphibian populations.
in PLoS pathogens
Jervis P
(2021)
Post-epizootic microbiome associations across communities of neotropical amphibians.
in Molecular ecology
Liew N
(2017)
Chytrid fungus infection in zebrafish demonstrates that the pathogen can parasitize non-amphibian vertebrate hosts.
in Nature communications
Luger M
(2008)
No evidence for precipitous declines of harlequin frogs ( Atelopus ) in the Guyanas
in Studies on Neotropical Fauna and Environment
Martel A
(2011)
Developing a safe antifungal treatment protocol to eliminate Batrachochytrium dendrobatidis from amphibians.
in Medical mycology
Mitchell KM
(2008)
Persistence of the emerging pathogen Batrachochytrium dendrobatidis outside the amphibian host greatly increases the probability of host extinction.
in Proceedings. Biological sciences
O'Hanlon SJ
(2018)
Recent Asian origin of chytrid fungi causing global amphibian declines.
in Science (New York, N.Y.)
Rosenblum EB
(2010)
A molecular perspective: biology of the emerging pathogen Batrachochytrium dendrobatidis.
in Diseases of aquatic organisms