The endangered Fleay's Barred Frog (Mixophyes fleayi), a species which has been affected by chytrid fungi. Photo by Laura Grogan.
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Amphibian chytrid fungus: impacts on Australian frogs and ongoing conservation challenges

Friday, 1 November 2019  | 

Since the mid-20th century, the fungal skin disease, chytridiomycosis (caused by Batrachochytrium dendrobatidis</em>; chytrid fungus) has been spread inadvertently by people, from SE Asia around the world. The disease has contributed to the decline of 501 amphibian species, including 90 presumed extinctions. In Australia, chytridiomycosis has contributed to the decline of 43 frog species, including seven presumed extinctions. The earliest detection of chytrid fungus in Australia is from 1978 near Brisbane. Chytrid fungus spread north and south, causing frog declines along the eastern ranges and in Tasmania; it is not associated with declines in Western Australia or the arid /semi-arid zones, and dies if exposed to temperatures >28oC or it dries out.

Outbreaks of chytridiomycosis can cause rapid population declines, however, chytrid fungus also persists in frog communities and can have long-term impacts. Frog communities can include tolerant hosts when adults or tadpoles harbor the fungus without suffering disease. These hosts can occur with more susceptible species and thereby maintain high infection rates in more susceptible individuals. This process is leading to decline to near extinction of at least six species in Australia, decades after initial outbreaks.

Chytrid fungus remains a threat for Australian frogs, with eradication unlikely, and elevated rates of death in impacted populations. There is limited evidence for protective immune responses or the evolution of resistance or tolerance to infection in susceptible species. Preventing further extinctions requires improved biosecurity and the development of effective mitigation. Potential strategies include increasing an individual’s capacity to withstand infection (e.g. probiotics), reducing environmental suitability for chytrid fungus (e.g. altering water salinity), or reducing other threats (e.g. increase breeding and survival to outweigh deaths caused by the disease). Investment is needed to develop and implement these strategies.

Supporting Research

Title
Aims
de Castro F. & Bolker B. (2005) Mechanisms of disease-induced extinction. Ecol. Lett. 8, 117-26.
To review and compare the importance of key theoretical and empirically demonstrated mechanisms promoting disease-associated declines and extinction of natural populations.
Grogan L. F., Robert J., Berger L., Skerratt L. F., Scheele B. C., Castley J. G., Newell D. A. & McCallum H. I. (2018) Review of the amphibian immune response to chytridiomycosis, and future directions. Front. Immunol. 9, 2536.
To overview expected immunological responses to fungal infection in amphibians, and provide a synthesis of current knowledge of host responses in the amphibian-chytridiomycosis system.
Blaustein A., Urbina J., Snyder P., Reynolds E., Dang T., Hoverman J., Han B., Olson D., Searle C. & Hambalek N. (2018) Effects of Emerging Infectious Diseases on Amphibians: A Review of Experimental Studies. Diversity 10, 81.
To review the effects of Batrachochytrium dendrobatidis, Batrachochytrium salamandrivorans and ranaviruses on amphibian hosts as demonstrated through experimental studies.
Murray K. A., Retallick R. W. R., Puschendorf R., Skerratt L. F., Rosauer D., McCallum H. I., Berger L., Speare R. & VanDerWal J. (2011) Assessing spatial patterns of disease risk to biodiversity: Implications for the management of the amphibian pathogen, Batrachochytrium dendrobatidis. J. Appl. Ecol. 48, 163-73.
To predict the potential geographic distribution of Batrachochytrium dendrobatidis infection using environmental suitability modelling, based on > 10,000 observations, Australia-wide.
Rachowicz L. J. & Vredenburg V. T. (2004) Transmission of Batrachochytrium dendrobatidis within and between amphibian life stages. Dis. Aquatic Org. 61, 75-83.
Laboratory chytrid fungus exposure experiments and associated field-survey study on Rana muscosa to investigate (1) conspecific transmission between tadpoles and from tadpoles to metamorphs, (2) effects of infection on both stages, and (3) document mouthpart pigment loss caused by chytrid fungus in tadpoles.
Raberg L., Graham A. L. & Read A. F. (2009) Decomposing health: tolerance and resistance to parasites in animals. Philos. Trans. R. Soc. B-Biol. Sci. 364, 37-49.
To (1) define a framework for analysis of tolerance in animals, (2) review evidence for variation of tolerance in animals and underlying mechanisms, and (3) highlight future avenues for research.
Savage A. E. & Zamudio K. R. (2016) Adaptive tolerance to a pathogenic fungus drives major histocompatibility complex evolution in natural amphibian populations. Proc. R. Soc. B Biol. Sci. 283.
To examine whether major histocompatibility complex (MHC) class II alleles and supertypes that are associated with chytridiomycosis susceptibility in controlled laboratory experiments similarly associate with chytrid fungus survival in natural field populations and demonstrate a signal of positive selection (Lithobates yavapaiensis).
Wilber M. Q., Knapp R. A., Toothman M. & Briggs C. J. (2017) Resistance, tolerance and environmental transmission dynamics determine host extinction risk in a load-dependent amphibian disease. Ecol. Lett. 20, 1169-81.
To test the hypothesis that with load-dependent wildlife diseases, resistant or tolerant hosts will experience reduced extinction risk, despite high transmission rates.
Berger L., Speare R., Daszak P., Green D. E., Cunningham A. A., Goggin C. L., Slocombe R., Ragan M. A., Hyatt A. D., McDonald K. R., Hines H. B., Lips K. R., Marantelli G. & Parkes H. (1998) Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America. Proc. Natl. Acad. Sci. USA 95, 9031-6.
Determine the cause of mortality in dying rainforest frogs
Richards S. J., McDonald K. R. & Alford R. A. (1993) Declines in populations of Australia's endemic tropical rainforest frogs. Pac. Conserv. Biol. 1, 66-77.
Quantify declines in frog species endemic to the Wet Tropics of Australia
Hoskin C. J., Hines H. B., Webb R. J., Skerratt L. F. & Berger L. (2019) Naïve rainforest frogs on Cape York, Australia, are at risk of the introduction of amphibian chytridiomycosis disease. Aust. J. Zool. 66, 174-8.
Determine whether chytrid fungus is present in the Cape Melville region of Queensland, Australia.
Scheele B. C., Hunter D. A., Grogan L., Berger L., Kolby J., McFadden M., Marantelli G., Skerratt L. F. & Driscoll D. A. (2014) Interventions for reducing extinction risk in chytridiomycosis-threatened amphibians. Conserv. Biol. 28, 1195–205.
To provide a conceptual underpinning for developing and trialing mitigation actions for amphibian species threatened by chytrid fungus
Scheele B. C., Skerratt L. F., Grogan L. F., Hunter D. A., Clemann N., McFadden M., Newell D., Hoskin C. J., Gillespie G. R. & Heard G. W. (2017) After the epidemic: Ongoing declines, stabilizations and recoveries in amphibians afflicted by chytridiomycosis. Biol. Conserv. 206, 37-46.
Assess long-term impacts of chytrid fungus in Australian frogs and review mechanisms underpinning ongoing species declines, stabilizations and recoveries
Skerratt L., Berger L., Clemann N., Hunter D., Marantelli G., Newell D., Philips A., McFadden M., Hines H., Scheele B., Brannelly L., Speare R., Versteegen S., Cashins S. & West M. (2016) Priorities for management of chytridiomycosis in Australia: saving frogs from extinction. Wildl. Res. 43, 105-20.
To guide the development of a coordinated national approach to inform the conservation of Australian frog species threatened by chytrid fungus
Scheele B. C., et al. (2019) Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity. Science 363, 1459-63.
Quantify the global-scale impact of chytrid fungus on amphibians
Becker, G. & Zamudio,K. R. (2011) Tropical amphibian populations experience higher disease risk in natural habitats. Proceedings of the National Academy of Sciences,108.
To examine the effect of habitat loss on chytrid fungus infection in tropical amphibian populations at both large and small spatial scales.
Heard G.W., Scroggie M.P., Clemann N., Ramsey D.S.L. (2014) Wetland characteristics influence disease risk for a threatened amphibian. Ecological Applications,24.
To identify intrinsic and extrinsic determinants of the probability and intensity of chytrid fungus infections in Litoria raniformis.
Kriger, K. M., Pereoglou, F., Hero, J. M. (2007) Latitudinal variation in the prevalence and intensity of chytrid (Batrachochytrium dendrobatidis) infection in eastern Australia Conservation Biology,21.
To describe chytrid fungus prevalence and intensity affecting some species along a latitudinal gradient, and identify factors that might be responsible for the variation in infection levels in Litoria lesueuri.
Pauza M.D., Driessen M.M., Skerratt L.F. (2010) Distribution and risk factors for spread of amphibian chytrid fungus Batrachochytrium dendrobatidis in the Tasmanian wilderness world heritage area, Australia. Diseases of Aquatic Organisms,92.
To determine the presence and distribution of chytrid fungus within and immediately around the Tasmanian Wilderness World Heritage Area, and identify risk factors associated with the distribution of the disease.
Puschendorf, R., Hoskin. C.J., Cashins, S.D., Mcdonald, K., Skerratt, L.F., Vanderwal, J., Alford, R. (2011) Environmental refuge from disease-driven amphibian extinction. Conservation Biology,25(5):956–64.
To examine the presence of chytrid fungus affecting two species of torrent frogs in new habitats and compare it to historical sites that experienced chytrid fungus extirpations.
Stockwell, M.P., Bower, D.S., Bainbridge, L., Clulow, J., Mahony, M. J. (2015) Island provides a pathogen refuge within climatically suitable area. Biodiversity conservation,24(10):2583–92.
To identify the infection status of chytrid fungus in four of the largest remaining populations of Litoria aurea.
Stockwell, M.P., Clulow, J., Mahony, M.J. (2015) Evidence of a salt refuge: chytrid infection loads are suppressed in hosts exposed to salt. Oecologia,177(3):901–10.
To identify aspects of the environment that reduce the infection prevalence and load of chytrid fungus in susceptible hosts.
Woodhams, D. C., Alford, R. A. (2005) Ecology of chytridiomycosis in Rainforest stream frog assemblages of Tropical Queensland. Conservation Biology,19.
To determine the current extent and prevalence of chytrid fungus in frog assemblages.
Murray K. A., Retallick R. W. R., Puschendorf R., Skerratt L. F., Rosauer D., McCallum H. I., Berger L., Speare R. & VanDerWal J. (2011) Assessing spatial patterns of disease risk to biodiversity: Implications for the management of the amphibian pathogen, Batrachochytrium dendrobatidis. J. Appl. Ecol. 48, 163-73.
To predict the potential geographic distribution of Batrachochytrium dendrobatidis infection using environmental suitability modelling, based on > 10,000 observations, Australia-wide.
Berger L., Speare R., Daszak P., Green D. E., Cunningham A. A., Goggin C. L., Slocombe R., Ragan M. A., Hyatt A. D., McDonald K. R., Hines H. B., Lips K. R., Marantelli G. & Parkes H. (1998) Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America. Proc. Natl. Acad. Sci. USA 95, 9031-6.
Determine the cause of mortality in dying rainforest frogs
Scheele B. C., Skerratt L. F., Grogan L. F., Hunter D. A., Clemann N., McFadden M., Newell D., Hoskin C. J., Gillespie G. R. & Heard G. W. (2017) After the epidemic: Ongoing declines, stabilizations and recoveries in amphibians afflicted by chytridiomycosis. Biol. Conserv. 206, 37-46.
Assess long-term impacts of chytrid fungus in Australian frogs and review mechanisms underpinning ongoing species declines, stabilizations and recoveries
Skerratt L., Berger L., Clemann N., Hunter D., Marantelli G., Newell D., Philips A., McFadden M., Hines H., Scheele B., Brannelly L., Speare R., Versteegen S., Cashins S. & West M. (2016) Priorities for management of chytridiomycosis in Australia: saving frogs from extinction. Wildl. Res. 43, 105-20.
To guide the development of a coordinated national approach to inform the conservation of Australian frog species threatened by chytrid fungus
Full reference
Aim
Type of Study
Key Results
Recommendations
Ecosystem and location
Reviewer
Scheele B. C., Hunter D. A., Brannelly L. A., Skerratt L. F. & Driscoll D. A. (2017) Reservoir‐host amplification of disease impact in an endangered amphibian. Conserv. Biol. 31, 592-600.
To (1) determine via laboratory experiment and field surveys whether Crinia signifera is a potential reservoir host for chytrid fungus, (2) determine via field surveys whether C. signifera presence associates with increased chytrid fungus prevalence in sympatric Pseudophryne pengilleyi populations, and (3) determine whether C. signifera abundance spatially associates with P. pengilleyi declines.
Laboratory experiment and field surveys
Reservoir species can promote declines of susceptible sympatric species through pathogen-mediated apparent competition. Crinia signifera was found to be a reservoir species for chytrid fungus - they maintained infection for 12 weeks without disease-associated mortality, their chytrid fungus prevalence and infection intensities were high, and they persisted at sites where P. pengilleyi had been extirpated or experienced declines.
Sites lacking reservoir hosts may provide important refugia. Identifying reservoir hosts and mapping their distributions will assist in identifying such refugia.
Frost-hollow grasslands, narrow seeps and open bogs in temperate highlands of southeastern Australia.
Laura Grogan
To review and compare the importance of key theoretical and empirically demonstrated mechanisms promoting disease-associated declines and extinction of natural populations.
Review paper
Murray K. A., Retallick R. W. R., Puschendorf R., Skerratt L. F., Rosauer D., McCallum H. I., Berger L., Speare R. & VanDerWal J. (2011) Assessing spatial patterns of disease risk to biodiversity: Implications for the management of the amphibian pathogen, Batrachochytrium dendrobatidis. J. Appl. Ecol. 48, 163-73.
To predict the potential geographic distribution of Batrachochytrium dendrobatidis infection using environmental suitability modelling, based on > 10,000 observations, Australia-wide.
Berger L., Speare R., Daszak P., Green D. E., Cunningham A. A., Goggin C. L., Slocombe R., Ragan M. A., Hyatt A. D., McDonald K. R., Hines H. B., Lips K. R., Marantelli G. & Parkes H. (1998) Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America. Proc. Natl. Acad. Sci. USA 95, 9031-6.
Determine the cause of mortality in dying rainforest frogs
Scheele B. C., Skerratt L. F., Grogan L. F., Hunter D. A., Clemann N., McFadden M., Newell D., Hoskin C. J., Gillespie G. R. & Heard G. W. (2017) After the epidemic: Ongoing declines, stabilizations and recoveries in amphibians afflicted by chytridiomycosis. Biol. Conserv. 206, 37-46.
Assess long-term impacts of chytrid fungus in Australian frogs and review mechanisms underpinning ongoing species declines, stabilizations and recoveries
Skerratt L., Berger L., Clemann N., Hunter D., Marantelli G., Newell D., Philips A., McFadden M., Hines H., Scheele B., Brannelly L., Speare R., Versteegen S., Cashins S. & West M. (2016) Priorities for management of chytridiomycosis in Australia: saving frogs from extinction. Wildl. Res. 43, 105-20.
To guide the development of a coordinated national approach to inform the conservation of Australian frog species threatened by chytrid fungus
To (1) determine via laboratory experiment and field surveys whether Crinia signifera is a potential reservoir host for chytrid fungus, (2) determine via field surveys whether C. signifera presence associates with increased chytrid fungus prevalence in sympatric Pseudophryne pengilleyi populations, and (3) determine whether C. signifera abundance spatially associates with P. pengilleyi declines.
Reservoir species can promote declines of susceptible sympatric species through pathogen-mediated apparent competition. Crinia signifera was found to be a reservoir species for chytrid fungus - they maintained infection for 12 weeks without disease-associated mortality, their chytrid fungus prevalence and infection intensities were high, and they persisted at sites where P. pengilleyi had been extirpated or experienced declines.
Murray K. A., Retallick R. W. R., Puschendorf R., Skerratt L. F., Rosauer D., McCallum H. I., Berger L., Speare R. & VanDerWal J. (2011) Assessing spatial patterns of disease risk to biodiversity: Implications for the management of the amphibian pathogen, Batrachochytrium dendrobatidis. J. Appl. Ecol. 48, 163-73.
To predict the potential geographic distribution of Batrachochytrium dendrobatidis infection using environmental suitability modelling, based on > 10,000 observations, Australia-wide.
Berger L., Speare R., Daszak P., Green D. E., Cunningham A. A., Goggin C. L., Slocombe R., Ragan M. A., Hyatt A. D., McDonald K. R., Hines H. B., Lips K. R., Marantelli G. & Parkes H. (1998) Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America. Proc. Natl. Acad. Sci. USA 95, 9031-6.
Determine the cause of mortality in dying rainforest frogs
Scheele B. C., Skerratt L. F., Grogan L. F., Hunter D. A., Clemann N., McFadden M., Newell D., Hoskin C. J., Gillespie G. R. & Heard G. W. (2017) After the epidemic: Ongoing declines, stabilizations and recoveries in amphibians afflicted by chytridiomycosis. Biol. Conserv. 206, 37-46.
Assess long-term impacts of chytrid fungus in Australian frogs and review mechanisms underpinning ongoing species declines, stabilizations and recoveries
Skerratt L., Berger L., Clemann N., Hunter D., Marantelli G., Newell D., Philips A., McFadden M., Hines H., Scheele B., Brannelly L., Speare R., Versteegen S., Cashins S. & West M. (2016) Priorities for management of chytridiomycosis in Australia: saving frogs from extinction. Wildl. Res. 43, 105-20.
To guide the development of a coordinated national approach to inform the conservation of Australian frog species threatened by chytrid fungus
To (1) determine via laboratory experiment and field surveys whether Crinia signifera is a potential reservoir host for chytrid fungus, (2) determine via field surveys whether C. signifera presence associates with increased chytrid fungus prevalence in sympatric Pseudophryne pengilleyi populations, and (3) determine whether C. signifera abundance spatially associates with P. pengilleyi declines.
Reservoir species can promote declines of susceptible sympatric species through pathogen-mediated apparent competition. Crinia signifera was found to be a reservoir species for chytrid fungus - they maintained infection for 12 weeks without disease-associated mortality, their chytrid fungus prevalence and infection intensities were high, and they persisted at sites where P. pengilleyi had been extirpated or experienced declines.
Murray K. A., Retallick R. W. R., Puschendorf R., Skerratt L. F., Rosauer D., McCallum H. I., Berger L., Speare R. & VanDerWal J. (2011) Assessing spatial patterns of disease risk to biodiversity: Implications for the management of the amphibian pathogen, Batrachochytrium dendrobatidis. J. Appl. Ecol. 48, 163-73.
To predict the potential geographic distribution of Batrachochytrium dendrobatidis infection using environmental suitability modelling, based on > 10,000 observations, Australia-wide.
Berger L., Speare R., Daszak P., Green D. E., Cunningham A. A., Goggin C. L., Slocombe R., Ragan M. A., Hyatt A. D., McDonald K. R., Hines H. B., Lips K. R., Marantelli G. & Parkes H. (1998) Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America. Proc. Natl. Acad. Sci. USA 95, 9031-6.
Determine the cause of mortality in dying rainforest frogs
Scheele B. C., Skerratt L. F., Grogan L. F., Hunter D. A., Clemann N., McFadden M., Newell D., Hoskin C. J., Gillespie G. R. & Heard G. W. (2017) After the epidemic: Ongoing declines, stabilizations and recoveries in amphibians afflicted by chytridiomycosis. Biol. Conserv. 206, 37-46.
Assess long-term impacts of chytrid fungus in Australian frogs and review mechanisms underpinning ongoing species declines, stabilizations and recoveries
Skerratt L., Berger L., Clemann N., Hunter D., Marantelli G., Newell D., Philips A., McFadden M., Hines H., Scheele B., Brannelly L., Speare R., Versteegen S., Cashins S. & West M. (2016) Priorities for management of chytridiomycosis in Australia: saving frogs from extinction. Wildl. Res. 43, 105-20.
To guide the development of a coordinated national approach to inform the conservation of Australian frog species threatened by chytrid fungus
To (1) determine via laboratory experiment and field surveys whether Crinia signifera is a potential reservoir host for chytrid fungus, (2) determine via field surveys whether C. signifera presence associates with increased chytrid fungus prevalence in sympatric Pseudophryne pengilleyi populations, and (3) determine whether C. signifera abundance spatially associates with P. pengilleyi declines.
Reservoir species can promote declines of susceptible sympatric species through pathogen-mediated apparent competition. Crinia signifera was found to be a reservoir species for chytrid fungus - they maintained infection for 12 weeks without disease-associated mortality, their chytrid fungus prevalence and infection intensities were high, and they persisted at sites where P. pengilleyi had been extirpated or experienced declines.