Amphibians can acquire resistance to deadly fungus

NSF | JULY 14, 2014

Emerging fungal pathogens pose a greater threat to biodiversity than any other parasitic group, scientists say, causing population declines of amphibians, bats, corals, bees and snakes. Now, research results reveal that amphibians can acquire behavioral or immunological resistance to a deadly chytrid fungus implicated in global amphibian population declines.

The critically endangered booroolong frog is capable of acquiring resistance to the fungus. Credit: Wikimedia Commons.

"Acquired resistance is important because it is the basis of vaccination campaigns based on 'herd immunity,' where immunization of a subset of individuals protects all from a pathogen," said Jason Rohr, a biologist at the University of South Florida (USF) who led the research team along with Taegan McMahon of the University of Tampa.

Experiments in the study revealed that after just one exposure to the chytrid fungus, frogs learned to avoid the deadly pathogen.

In further experiments in which frogs could not avoid the fungus, frog immune responses improved with each fungal exposure and infection clearance, significantly reducing fungal growth and increasing the likelihood that the frogs would survive subsequent chytrid infections.

The amphibian chytrid fungus suppresses the immune responses of amphibian hosts, so many researchers doubted that amphibians could acquire effective immunity against this pathogen.

Amphibians can acquire immunological resistance that overcomes chytrid-induced immunosuppression and increases survival.

Variation in the degree of acquired resistance might partly explain why fungal pathogens cause extinctions of some animal populations but not others.

Conservationists have collected hundreds of amphibian species threatened by the fungus and are maintaining them in captivity with the hope of re-establishing them in the wild.

But reintroduction efforts so far have failed because of the persistence of the fungus at collection sites.

Immune responses to fungi are similar across vertebrates, and many animals are capable of learning to avoid natural enemies.

The findings offer hope that amphibians and other wild animals threatened by fungal pathogens--such as bats, bees and snakes--might be capable of acquiring resistance to fungi and so might be rescued by management approaches based on herd immunity.

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