Scientists find frog genes that provide immunity to extinction plague

Jeremy Hance
September 27, 2011

 Scientist trying to save a Hyloscirtus colymba tree frog, a species imperiled by chytridiomycosis at Panama's Amphibian Rescue and Conservation Project. Photo by: Rhett A. Butler.
Scientist trying to save a La Loma tree frog, a species imperiled by chytridiomycosis at Panama's Amphibian Rescue and Conservation Project. Photo by: Rhett A. Butler.

Scientists with Cornell have discovered genetics that may provide immunity to frogs in face of the killer amphibian-disease chytridiomycosis. This plague, which is spreading to amphibian populations worldwide, is responsible for a number of frog species' recent extinction. But now researchers report in a new study in the Proceedings of the National Academy of Sciences (PNAS) that they are one step closer to understanding why some frog populations are able to fend off the disease, while others succumb with lightning-speed. In time, the results may lead to breeding strategies in captivity that could produce immune populations.

Researchers collected lowland leopard frogs (Lithobates yavapaiensis) from five populations in Arizona. In the lab they tested the frogs with chytridiomycosis, which is caused by the fungus Batrachochytrium dendrobatidis. Three of the populations died, but two populations withstood the infection. Investigating the populations, researchers found that a particular genetic code within the frogs' major histocompatibility complex (MHC) may be key.

MHC is a protein in all vertebrates that alerts the body's immune system to disease; lead researcher, Ann Savage, explained to the BBC that MHC was like a 'gatekeeper' for immunity. However MHC is only capable of recognizing certain diseases: those it doesn't catch run amok. Capable of recognizing chytridiomycosis and fending it off, the surviving frogs had different genetic signatures than those who perished.

With further research, scientists hope to use the understanding of how frogs' develop immunity against chytridiomycosis to protect captive populations from the disease. Scientists have recently brought many frog species into captivity in an effort to save them from extinction. The plan is one day to reintroduce these populations back into the wild once their security against chytridiomycosis can be assured. That hope may now be closer to a reality.

Amphibians are among the world's most imperiled taxa. Along with chytridiomycosis, amphibians face deforestation, habitat loss, pollution, overexploitation and climate change. Given their unique lifestyle, amphibians are incredibly sensitive to changes in both their terrestrial and aquatic environments. Currently the IUCN Red List has found that 41 percent of the world's 7,000 amphibians are threatened with extinction. It's believed that at least 120 amphibians have gone extinct in the last 30 years, and some species likely vanished before they were ever discovered.

CITATION: Anna E. Savage and Kelly R. Zamudio. MHC genotypes associate with resistance to a frog-killing fungus. PNAS. PNAS 2011 : 1106893108v1-201106893.

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Jeremy Hance
mongabay.com (September 27, 2011).

Scientists find frog genes that provide immunity to extinction plague .