Before you read this, if you want to know how chytrid spread around the world, here’s a good previous post on that. Click HERE. Now, back to the topic at hand…
The amphibian animal class was the superman of evolution. Amphibians were here when the dinosaurs went extinct, and until 20 years ago were just an assumption — you’d find them everywhere. But their kryptonite has emerged in a killer frog fungus named chytrid that is contributing to their demise — a looming mass extinction that would be second in significance to the doom on dinosaurs. It’s been written about hundreds of times.
Scientists are working on a cure for chytrid, and part of the answer may have been just discovered. The BBC News reports today that a bacteria, Janthinobacterium lividum, is helping frogs live much longer after being exposed to chytrid (batrachochytrium dendrobatidis). An excerpt from the report:
The chytrid fungus is a major reason for the global decline which sees one third of amphibians facing extinction.
But the latest findings, reported at the American Society for Microbiology meeting in Boston, may give conservationists a new way to tackle the scourge.
Reid Harris and colleagues found that treating the mountain yellow-legged frog (Rana muscosa) with extra helpings of bacteria reduces the weight loss seen when the fungus attacks, and appears to keep them alive longer as well.
“In the group we exposed to chytrid, about 50% to 60% have died,” he told BBC News.
“But of the ones where we added the bacterium (Janthinobacterium lividum) none have died, and we’re about 140 days in now.”
The mountain yellow-legged frog of the Sierra Nevada mountains in the western US is categorised as Critically Endangered, with numbers believed to have fallen by 80% within about 15 years.
The waterborne fungus Batrachochytrium dendrobatidis has emerged as a major threat to amphibians in the last decade, and conservationists have been left grasping for a way of stopping its apparently inexorable worldwide spread.
But although it has devastated many species, some appear to have an innate capacity to withstand infection. Even within species that generally succumb, the odd population survives.
What gives these communities immunity is not clear; but one answer, as Professor Harris’s group has been finding, could be bacteria such as Janthinobacterium which live naturally on their skin.
Earlier lab experiments, also involving the red-backed salamander (Plethodon cinereus), showed that the bacteria produce chemicals able to attack the fungus.
“We detected anti-chytrid metabolites on the skin itself in high enough concentrations to kill off the chytrid,” he said.
“One of our hypotheses is that the bacteria live in some kind of defensive symbiosis with the frogs and salamanders.”
Another piece of evidence came with the finding that amphibians in colonies which survive the passage of the chytrid wave tend to carry higher levels of the bacteria.
This all raises questions as to why, if the bacteria are protective, they are not present in large enough numbers in all colonies; and whether some other factor – perhaps habitat loss, pollution or rapid climatic shifts – can reduce the bacterial cargo, opening up the door to fungal attack.
In Spain, scientists have found that rising temperatures appear to increase amphibians’ vulnerability to infection.