Global warming fuels fungal toad-killer

• 00:01 25 October 2006
• NewScientist.com news service
• John Pickrell

Climate and disease have driven the decline of Spain's midwife toad - so-called for the male's habit of carrying a string of fertilised eggs on his back (Image: Jaime Bosch)

Midwife toads were once common in Spain's Penalara Natural Park, but are dwindling due to a deadly fungal disease (Image: Jaime Bosch)

The first evidence in Europe of a species decline from a disease linked to climate change has been shown, researchers say.

A new 26-year-long study of midwife toads (Alytes obstetricans) in Spain, shows that rising temperatures are tightly linked to the impact of a deadly fungal disease.

Earlier this year, researchers found a similar correlation between the timing of frog extinctions from the same disease on South American mountains and increased temperatures in the region (see Global warming boosts fungal epidemic in frogs).

The chytrid fungus Batrachochytrium dendrobatidis is a fatal pathogen of amphibians that interferes with their ability to control water loss. It is credited with wiping out frogs and their kin in vast numbers in Australia and South America. The disease has killed 74 of Central and South America's 110 harlequin frog species since the 1980s, for example.

Invading Europe

Within the last decade, it has been gaining a foothold in Europe too. As a result of the fungus, the midwife toad is now virtually extinct on mountains in Spain's Penalara Natural Park, where it once thrived.

Jaime Bosch at the National Museum of Natural Science in Madrid, Spain, and colleagues compared records for toad die-offs in Penalara with meteorological data for the mountains between 1976 and 2002. They found a strong correlation with rising temperatures and increased impact of the fungus.

"This [infection] is the clearest and best example of climate change being linked to an infectious disease," says Matthew Fisher, a team member at Imperial College London, UK.

Warm and dry

Amphibians are cold-blooded, making them much more susceptible to environmental changes in temperature, says Fisher. Temperature fluctuations render them less well-equipped to defend themselves against disease, he believes. In addition, recent mild winters may be allowing the fungus to survive from year to year, when previously it would not have.

"Warmer and drier environments might induce physiological stress in amphibians that would make these animals more susceptible to fungal infection or exacerbate the negative effects of infection," agrees herpetologist James Hanken at Harvard University in Cambridge, Massachusetts, US.

"The researchers demonstrate a striking association between a climate variable and recorded epidemics of the chytrid fungus," he adds.

Parks and preserves

"Declines of amphibian populations, especially those occurring in seemingly undisturbed areas since the 1970s, have been perplexing and alarming," says ecologist Alan Pounds at Monteverde Cloud Forest Preserve in Costa Rica.

"[These declines] show that setting aside parks and preserves alone is not enough to assure species survival," Pounds adds. His research group discovered the link between climate and frog extinctions in South America.

Bosch and Fisher now plan to carry out a much wider survey of the impact of the disease in amphibians across Europe.

Though experts are unsure why the fungal pandemic has spreading so rapidly from region to region, there is evidence that the international trade in frogs for food, pets and research is driving it (see Frogs legs are their undoing). Between 1998 and 2002, the US alone is thought to have imported 14.7 million wild amphibians.

Journal reference: Proceedings of the Royal Society B (DOI: 10.1098/rspb.2006.3713)