The extinction of 90 species of amphibians can be pinned on a deadly fungal disease, according to the most comprehensive exercise yet to map its impact.
In total, chytridiomycosis contributed to the decline of more than 500 species of frogs, toads and salamanders, or nearly 7 per cent of all amphibian species, since the disease first emerged in the 1980s.
The toll means the disease has wrought the greatest loss of biodiversity by any pathogen, on an order of magnitude greater than other wildlife diseases, such as the bat-killing white-nose syndrome.
“It’s crazy what this pathogen does,” says Trenton Garner from the Zoological Society of London, one of the paper’s authors.
Previous work has been undertaken on the spread of the disease, and regional efforts have been made to gauge its impact on frogs and other species. But the team behind the new study say it is the best effort yet to aggregate its effects globally. “It’s a smoking gun that wasn’t there before,” says Garner.
Small signs of hope
Chytridiomycosis is caused by two chytrid fungi called Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans. The fungi are believed to have emerged in Asia in the 1980s and the disease they cause spread rapidly, aided by globalisation and trade in wildlife, leading to a peak of amphibian deaths in the 1980s and a later spike in the noughties when it hit South America.
For many of the species that declined, the disease was the key driver. For others, it was a contributing factor along with pressures such as habitat loss and climate change.
Of the species that experienced declines, just 12 per cent have shown signs of recovery. “The recovery has to be put in context, it’s not like they are back to their original numbers. They are not roaring back,” says Garner.
There are small signs of hope. The number of new species hit by the disease is down. Some frogs appear to be evolving resistance to the disease, and antifungal treatments have been shown to work in some cases.
Ultimately, better biosecurity and a reduction in wildlife trade are what’s needed, says Garner. “We don’t have an effective strategy at treating it in the wild.”
Disease is far from the only threat to frogs and salamanders, which have suffered catastrophic declines in recent decades, primarily due to habitat loss. Climate change, another pressure, is also making them vulnerable to disease.