Friday, March 22, 2013

[Herpetology • 2013] Hot bodies protect amphibians against chytrid infection in nature


Green Eyed Tree Frog with radio-transmitter
photo: Jodi J L Rowley
http://australianmuseum.net.au

Environmental context strongly affects many host-pathogen interactions, but the underlying causes of these effects at the individual level are usually poorly understood. The amphibian chytrid fungus has caused amphibian population declines and extinctions in many parts of the world. Many amphibian species that have declined or have been extirpated by the pathogen in some environments coexist with it in others. Here we show that in three species of rainforest frogs in nature, individuals' probability of infection by the amphibian chytrid fungus was strongly related to their thermal history. Individuals' probability of infection declined rapidly as they spent more time above the pathogen's upper optimum temperature. This relationship can explain population-level patterns of prevalence in nature, and suggests that natural or artificial selection for higher thermal preferences could reduce susceptibility to this pathogen. Similar individual-level insights could improve our understanding of environmental context-dependence in other diseases.

Subject terms: Ecological epidemiology, Herpetology, Tropical ecology, Behavioural ecology

Rowley, J.J.L. & Alford, R.A. 2013. Hot bodies protect amphibians against chytrid infection in nature. Scientific Reports 3, 1515: DOI:10.1038/srep01515 

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Hot bodies protect frogs from disease

The amphibian chytrid fungus (Batrachochytrium dendrobatidis) is responsible for the often fatal amphibian disease chytridiomycosis. This disease has now been associated with declines and extinctions in hundreds of species of amphibians worldwide, and is a serious threat to global amphibian biodiversity.

However, not all amphibian species decline from chytridiomycosis, and many amphibians that have declined from the disease in some environments coexist with it in others. Why might this be?

One such reason is temperature. In the lab, the amphibian chytrid fungus grows best between 17-25°C and infected captive frogs can be cured by simply raising the temperature. Natural populations of frogs also appear to be affected by temperature, with infected frogs more often detected in cooler months and at higher (and therefore cooler) altitudes. So there’s reason to suspect that temperature may play an important role in determining whether individual frogs are infected with the amphibian chytrid fungus in nature.

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