Australasian Science: Australia's authority on science since 1938

Hot Frogs Beat Chytrid

By Stephen Luntz

Frogs with a body temperature above 25°C for extended periods of time are able to fend off the chytrid fungus in the wild, according to an Australian Museum study.

Batrachochytrium dendrobatidis (Bd) has already caused the extinction of many frog species, and Australian rainforest frogs have been particularly hard hit. The damage appears to have been greatest in high altitude rainforests, suggesting that cool and wet conditions present the greatest danger.

Bd grows best between 17°C and 25°C in the laboratory, so Dr Jodi Rowley set out to investigate whether body temperatures above this level offered protection. “One study has shown that after the first appearance of chytridiomycosis in a susceptible population, mean body temperatures of frogs increased, which should reduce the negative effects of the pathogen,” Rowley wrote in Nature.

“Increases in mean body temperature at the population level could reflect adaptive responses of individuals to infection, shifting thermal preferences to produce ‘behavioural fever’. However, it could also result from selective sweeps in which individuals that attain higher temperatures for other reasons are more likely to survive during outbreaks of chytridiomycosis.”

Rowley fitted 100 rainforest frogs with thermally sensitive radio-tracking devices and observed their movements using infrared guns. She found wide variations in their temperatures, depending on their ability to find a sunny spot to bask. The longer the frogs spent above 25°C the lower their rate of infection. After controlling for body temperature she found that there were no seasonal variations in infection rates.

Although global warming will raise temperatures for at-risk frogs, Rowley cautions that the benefits may be offset by greater cloudiness or changes to rainfall patterns.

Rowley says the fungus is generally less of a problem in temperature zones because non-rainforest frogs, while breeding in water, spend less time wet.

While the results will be useful for captive breeding programs, Rowley also suggests: “By carefully manipulating habitats to increase the availability of warmer temperatures, we may be able to help frogs reach temperatures that allow them to reduce or eliminate infection”.

Colonies of highly endangered species could be protected by creating breaks in the canopy or adding boulders where frogs can bask, although Rowley warns that making locations too attractive could backfire if predators catch on.