Frogs, salamanders, and toads across the world are now under attack from a widening range of interacting pathogens that threaten to devastate global amphibian populations.
That is the stark warning of leading zoological experts who will gather this week in London in a bid to establish an emergency plan to save these endangered creatures. “The world’s amphibians are facing a new crisis, one that is caused by attacks by multiple pathogens,” said Professor Trent Garner of the Zoological Society of London, which is hosting the conference. “We desperately need to devise strategies that can protect them.”
Thirty years ago experts noticed that amphibian populations were plunging in different areas of the world as an emerging fungal disease known as chytridiomycosis, or simply chytrid, began taking its toll of frogs and toads. At least 100 species have since been wiped off the face of the planet. These include the golden toad in Costa Rica (Incilius periglenes); the southern gastric-brooding frog of Australia (Rheobatrachus silus); and Arthur’s stubfoot toad (Atelopus arthuri) in Ecuador. Hundreds of other amphibian species have also suffered severe declines – as a result of chytrid infections.
But scientists also know chytrid is not the only cause of the amphibian deaths now occurring around the world. Another pathogen known as the ranavirus, which exists in at least four varieties, has been observed killing amphibians. In addition they found that there are at least two species of chytrid, and within these, many different genetic types.
“The crucial point is that these different pathogens are no longer acting alone,” added Garner. “They are interacting and in combination are killing off more and more amphibians. These interactions are often far worse than the effects of individual pathogens.”
Apart from the straightforward loss of species, reducing amphibian numbers is harmful to the environment because frogs, newts and toads play an important role in maintaining healthy ecosystems. For example, frogs eat mosquitos that spread disease. They also provide food for birds and other animals. In addition, tadpoles chew up algae and so help keep algal blooms at bay. “To date Britain has been pretty lucky,” said Garner. “There have been no recorded mass mortalities as there have been in other countries – at least as far as chytrid infections go.”
However, ranaviruses are a different issue, he added. They have been causing declines in the common frog (Rana temporaria) in the UK but also infect the common toad (Bufo bufo), often with fatal results. As a result, zoologists have asked the public to report sightings of sick or dead amphibians via websites such as Garden Wildlife Health and have also urged people not to move eggs, tadpoles or frogs from pond to pond.
“That way, you avoid spreading infections,” Garner said. “Anything that you can do to reduce pressure on these creatures is important.”
In addition, this week’s conference – Mitigating single pathogen and co-infections that threaten amphibian biodiversity – will try to outline ideas for trying to save amphibians from the multipathogen threats that they now face. “We will be holding a full-day workshop in which we get the very best people in the field – conservationists, zoologists and experts on co-infections together and get them to hammer out the best strategy for dealing with this. Unless we get one, this is going to get a lot worse.”