Climate change driving toad disease from fungus in Pyrenees

Date: October 23, 2016

Source: Imperial College London

At high altitudes, frogs and toads are being infected by a deadly chytrid fungus at increasingly high rates in the Pyrenees Aspe Valley, France. The spike in mortality of these toads is blamed on warming in these mountains, which drives fungal infection in frogs and toads, and is expected to get worse.

Following years of speculation that climate change was driving deaths by chytrid, this eight-year study by researchers at Imperial College London and ZSL (Zoological Society of London), published in the Philosophical Transactions of the Royal Society B, is the first to compare temperature with amounts of disease in order to infer future patterns at high altitudes. The fungus Batrachochytrium dendrobatidis (Bd) has severely affected over 700 amphibian species worldwide causing more extinction events than any other infectious disease known to science.

From analysing lake melt and amphibian infection rates over eight years, the researchers found that the earlier that the valley's lakes melted in the springtime, the higher were the rates of infection for both frogs and toads.

They then created predictive climate models that focused on regional temperatures across this part of the Pyrenees mountains. This research predicted that the region will continue to warm significantly and that frozen lakes will become increasingly rare, meaning that the midwife toad tadpoles in these lakes will spend increasingly less time under ice, with the effect that they multiply the effects of Bd infection in other species of frogs and toad.

Although the link between lake melt and rates of Bd infection is clear, it isn't known why temperature has this effect. Theories range from whether warmer lakes provide the ideal temperatures for chytrid growth, to whether predators of chytrid fungal zoospores are less active in warmer lakes.

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