Amphibian Die Off: Chytrid Fungi

Bio 102 Lab Case Study

Scanning electron micrograph of a frozen intact zoospore and sporangia of the chytrid fungus (Batrachochytrium dendrobatidis), CSIRO from Wikipedia

Chytridomycosis• Infectious disease of amphibian

caused by Batrachochytrium dendrobatidis (Bd) (Daszak et al. 2003).

• First found in Australia in 1998 devastating amphibian populations (Berger et al. 1998)

• Specific to amphibians• One of two species of chytrid known

to infect vertebrates (Raphael and Pramuk, 2007)– Other infects fish

• Bd is spreading world wide• Responsible for greatest disease

induced biodiversity loss in recorded history (Skerratt et al. 2007)– Extinction of over 200 species of frogs

Dead Bd-infected Atelopus limosus at Sierra Llorona (posed to show ventral lesions and chytridiomycosis signs), photo by Brian Gratwicke

New species targets salamanders

Questions

1. What phylum of fungi is responsible for chytridiomycosis?2. Why is this fungi successful at killing amphibians?3. Why be concerned about the world’s amphibian populations?

What role do amphibians play in ecosystems?

Origin of Bd• Not exactly known• Found in Xenopus laevis which

are used in labs, and previously were important for pregnancy testing– Inject frog with human female

urine. If frog laid eggs a few hours later, human female was pregnant (Rogers, 2013)

• Also used in fishing as trade increased

• Weldon et al. (2004) found museum specimens with Bd dating back to 1938

1. How might Bd be spreading through the environment?

2. Propose a hypothesis that would explain why Bd is spreading like a new disease throughout the world

How does Bd spread?• Not exactly known, but likely human induced• Pet trade, fishing trade, human consumption of bullfrogs, scientific

trade (Reed et al. 2005, Weldon et al. 2004)• Pico and Collins (2008)—positive Bd water samples from bait shops• Inadvertent through produce trade—Occurred in Tasmania in 1993

(Pauza and Driessen, 2008)• Tree frog in a banana box in Tasmania imported from Australia was

captured and developed Bd (Obendorf 2005)• An estimated 50,000 frogs per year are accidentally carried in

produce (McDonald and Speare 2000), and up to 70% are released at their destination (O’Dwyer et al., 2000)

• Tasmania—associated with gravel roads sprayed with water from wetlands, and moist soil transported (Pauza and Driessen, 2008)

Other scientists areindicating that Bdmay be spreadingdue to climatechange. How mightthis happen?

A chytrid-infected frog, Forrest Brem

Climate Change and Bd

• Temperatures warm, and organisms shift upward in elevation, or toward the poles, especially if ponds dry up (Parmesan, 2006)– May introduce Bd to other areas

• In Andes, deglaciation—amphibians into new areas at record elevation, one species has Bd with no side effects, other species Bd and die offs (Seimon et al., 2006)

Figure 1. Summary of Red List categories for all amphibians. The percentage of species in each category is displayed on the pie chart (from Stuart et al. 2008)

1. Some scientists are attempting to prevent the extinction of amphibians by capturing amphibians in the wild, breeding them in chytrid free labs, then releasing some of the amphibians into the wild. Discuss how such a strategy could save some species of amphibians.

2. How else might we prevent the spread of Bd throughout the world?

Works Cited • Davidson, E. W., Parris, M., Collins, J. P., Longcore, J. E., Pessier, A. P., and Brunner, J. 2003. Pathogenicity and transmission of chytridiomycosis in tiger salamanders

(Ambystoma tigrinum). Copeia 2003: 601-607.• 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., and Parkes, H. 1998. Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America. Proceedings of the National Academy of Sciences, USA. 95: 9031-9036.

• Raphael, B., and Pramuk, J. 2007. Treatment of chytrid infection in Typhlonectes spp. using elevated water temperatures. Proceedings of the IRCEB meeting, Phoenix, Arizona, November 2007. Unpublished.

• Skerratt, L. F., Berger, L., Speare, R., Cashins, S., McDonald, K. R., Phillott, A. D., Hines, H. B., and Kenyon, N. 2007. Spread of chytridiomycosis has caused the rapid global decline and extinction of frogs. EcoHealth 4: 125-134.

• Weldon, C. and du Preez, L.H. 2004. Decline of the Kihansi Spray Toad, from the Udzungwa Mountains, Tanzania. Froglog 62: 2-3.• Weldon, C., du Preez, L. H., Hyatt, A. D., Muller, R., and Speare, R. 2004. Origin of the amphibian chytrid fungus. Emerging Infectious Diseases 10: 2100-2105• Reed, K. D., Ruth, G. R., Meyer, J. A., and Shukla, S. K. 2005. Chlamydia pneumoniae infection in a breeding colony of African Clawed Frogs (Xenopus tropicalis).

2000. Emerging Infectious Diseases 6: 196-199.• Picco, A. M., and Collins, J. P. 2008. Amphibian commerce as a likely source of pathogen pollution. Conservation Biology 22: 1582-1589.• Obendorf, D. L. 2005. Developing field & diagnostic methods to survey for chytridiomycosis in Tasmanian frogs. Central North Field Naturalists, Inc. Tasmania,

Australia. Report to the Department of Environment and Heritage, Canberra. Available online.• O'Dwyer, W. T., Buttemer, W. A., and Priddel, D. M. 2000. Inadvertent translocation of amphibians in the shipment of agricultural produce into New South Wales: its

extent and conservation implications. Pacific Conservation Biology 6:40-45.• Pauza, M., and Driessen, M. 2008. Distribution and potential spread of amphibian chytrid fungus Batrachochytrium dendrobatidis in the Tasmanian Wilderness

World Heritage Area. Report on Amphibian Chytrid Fungus in the TWWHA, Department of Primary Industries, Parks, Water, and Environment. Available online.• Rogers, K. 2013. The First Pregnancy Tests and the Demise of Frogs.Encyclopedia Brittanica.

http://blogs.britannica.com/2013/05/the-first-pregnancy-tests-and-the-demise-of-frogs/• Seimon, T. A., Seimon, A., Daszak, P., Halloy, S. R. P., Schloegel, L. M., Aguilar, C. A., Sowell, P., Hyatt, A. D., Konecky, B., and Simmons, J. E. 2006. Upward range

extension of Andean anurans and chytridiomycosis to extreme elevations in response to tropical deglaciation. Global Change Biology 12: 1-12.• Parmesean, C. 2006. Ecological and Evolutionary Responses to Recent Climate Change. Annual Review of Ecology, Evolution, and• Systematics 37:637–69. • Stuart, S.N. et al. (2008). Threatened Amphibians of the World. Barcelona/Gland/Arlington: Lynx Edicions/IUCN/Conservation International.