Otto McDiesel
Well-known member
By ANNE MCILROY
Thursday, January 12, 2006 Page A3
SCIENCE REPORTER
When African clawed frogs are injected with urine from a pregnant woman, they ovulate, so in the 1950s they were shipped around the world to be used in pregnancy tests.
Today, a fungus they carried on their backs has been implicated in the mysterious deaths of frogs on four continents.
A new study has found that global warming is creating optimal conditions for the fungus -- called Batrachochytrium dendrobatidis, or amphibian chytrid fungus -- in the mountainous regions of Costa Rica and other similar environments where many species threatened with extinction live.
Hotter temperatures have led to more clouds during the day, which may make it hard for frogs to find a hot, dry place where the fungus can't grow. As well, warmer temperatures at night have created ideal growth conditions for the fungus, said Alan Pounds, a researcher at the Golden Toad Laboratory for Conservation in Costa Rica.
Researchers have long suspected that rising temperatures were playing a role in the outbreak of the fatal disease caused by the fungus, but couldn't figure out why, because the organism dies when temperatures hit 30 degrees. Dr. Pounds and his colleagues appear to have solved the puzzle: The cooler days and warmer nights on tropical mountainsides are to blame.
Roughly one-third of the world's 6,000 amphibian species are now considered under threat of extinction. Destruction of habitat is an important reason for this. But frogs are also disappearing in pristine, protected tropical forests. These are the mysterious extinctions that Dr. Pounds argues are linked to the fungus.
Does he believe he has solved the mystery of the disappearing frogs?
"I suspect so. We've taken a big step in that direction."
In today's edition of the respected British journal Nature, he reports that the Monteverde harlequin frog and the golden toad, which disappeared 17 years ago, were likely killed because climate change created ideal conditions for the fungus to grow. His analysis of weather data showed that two-thirds of the 110 harlequin frog species that have already vanished likely met the same fate.
"There may be a tragic irony here," U.S. researchers Andrew Blaustein and Andy Dobson wrote in an article accompanying the research paper.
"So it seems that the extinction of one frog species through trade may have led to the extinction of other amphibian species -- a totally unexpected, indirect consequence of human ingenuity."
The fungus has been put forward by other researchers as the potential cause of death in frog populations in Australia and Panama and has been associated with declines in Ecuador, Venezuela, New Zealand and Spain.
The "Out of Africa" theory hasn't been proven, said Dr. Pounds, who is more concerned about the effect the fungus is having on frogs than where it came from.
Preliminary genetic studies suggest it has spread relatively recently, which is why scientists believe it may be linked to the global trade in clawed frogs, he said. But it also may be endemic to a number of regions.
African frogs may be partially responsible for its spread, Dr. Pounds said. Some of the clawed frogs exported for pregnancy tests escaped. The theory is that they passed the fungus to hardier carriers, like bullfrogs, that in turn infected more susceptible frogs. It is thought that frogs that bask in the sun are more resistant, because dry conditions limit fungal growth.
Studies done on dead frogs in museums show that by the 1960s, the fungus was found in many parts of the world, including Canada. A frog from 1961 stored in a museum in St-Pierre-de-Wakefield, Que., was a carrier.
David Green, an expert in amphibian population biology at the Redpath Museum at McGill University in Montreal, is skeptical of the idea that the global trade in frogs is to blame for the spread of the fungus, especially in Canada, where African frogs wouldn't have lasted long in the cold. Scientists have found the fungus in northern leopard frogs in Alberta and several other species, but they don't have evidence that it has caused an outbreak of disease or that it is implicated in the decline of Canadian frogs.
Mr. Green said Dr. Pounds's paper is intriguing, however, because it offers the first explanation for why an organism that has been around for a long time only started causing outbreaks of disease in the 1980s, when frog populations around the world began their dramatic decline.
The discovery that African clawed frogs could be used in pregnancy tests came in the 1930s, and the global trade in the frogs grew dramatically in the 1950s.
Scientists aren't sure how the fungus kills frogs, although it thickens and damages their skin, and may interfere with their ability to absorb water."Disease is killing the frogs, but climate change is pulling the trigger," Dr. Pounds said. "Global warming is wreaking havoc on amphibians, and will cause staggering losses of biodiversity if we don't do something fast."
Thursday, January 12, 2006 Page A3
SCIENCE REPORTER
When African clawed frogs are injected with urine from a pregnant woman, they ovulate, so in the 1950s they were shipped around the world to be used in pregnancy tests.
Today, a fungus they carried on their backs has been implicated in the mysterious deaths of frogs on four continents.
A new study has found that global warming is creating optimal conditions for the fungus -- called Batrachochytrium dendrobatidis, or amphibian chytrid fungus -- in the mountainous regions of Costa Rica and other similar environments where many species threatened with extinction live.
Hotter temperatures have led to more clouds during the day, which may make it hard for frogs to find a hot, dry place where the fungus can't grow. As well, warmer temperatures at night have created ideal growth conditions for the fungus, said Alan Pounds, a researcher at the Golden Toad Laboratory for Conservation in Costa Rica.
Researchers have long suspected that rising temperatures were playing a role in the outbreak of the fatal disease caused by the fungus, but couldn't figure out why, because the organism dies when temperatures hit 30 degrees. Dr. Pounds and his colleagues appear to have solved the puzzle: The cooler days and warmer nights on tropical mountainsides are to blame.
Roughly one-third of the world's 6,000 amphibian species are now considered under threat of extinction. Destruction of habitat is an important reason for this. But frogs are also disappearing in pristine, protected tropical forests. These are the mysterious extinctions that Dr. Pounds argues are linked to the fungus.
Does he believe he has solved the mystery of the disappearing frogs?
"I suspect so. We've taken a big step in that direction."
In today's edition of the respected British journal Nature, he reports that the Monteverde harlequin frog and the golden toad, which disappeared 17 years ago, were likely killed because climate change created ideal conditions for the fungus to grow. His analysis of weather data showed that two-thirds of the 110 harlequin frog species that have already vanished likely met the same fate.
"There may be a tragic irony here," U.S. researchers Andrew Blaustein and Andy Dobson wrote in an article accompanying the research paper.
"So it seems that the extinction of one frog species through trade may have led to the extinction of other amphibian species -- a totally unexpected, indirect consequence of human ingenuity."
The fungus has been put forward by other researchers as the potential cause of death in frog populations in Australia and Panama and has been associated with declines in Ecuador, Venezuela, New Zealand and Spain.
The "Out of Africa" theory hasn't been proven, said Dr. Pounds, who is more concerned about the effect the fungus is having on frogs than where it came from.
Preliminary genetic studies suggest it has spread relatively recently, which is why scientists believe it may be linked to the global trade in clawed frogs, he said. But it also may be endemic to a number of regions.
African frogs may be partially responsible for its spread, Dr. Pounds said. Some of the clawed frogs exported for pregnancy tests escaped. The theory is that they passed the fungus to hardier carriers, like bullfrogs, that in turn infected more susceptible frogs. It is thought that frogs that bask in the sun are more resistant, because dry conditions limit fungal growth.
Studies done on dead frogs in museums show that by the 1960s, the fungus was found in many parts of the world, including Canada. A frog from 1961 stored in a museum in St-Pierre-de-Wakefield, Que., was a carrier.
David Green, an expert in amphibian population biology at the Redpath Museum at McGill University in Montreal, is skeptical of the idea that the global trade in frogs is to blame for the spread of the fungus, especially in Canada, where African frogs wouldn't have lasted long in the cold. Scientists have found the fungus in northern leopard frogs in Alberta and several other species, but they don't have evidence that it has caused an outbreak of disease or that it is implicated in the decline of Canadian frogs.
Mr. Green said Dr. Pounds's paper is intriguing, however, because it offers the first explanation for why an organism that has been around for a long time only started causing outbreaks of disease in the 1980s, when frog populations around the world began their dramatic decline.
The discovery that African clawed frogs could be used in pregnancy tests came in the 1930s, and the global trade in the frogs grew dramatically in the 1950s.
Scientists aren't sure how the fungus kills frogs, although it thickens and damages their skin, and may interfere with their ability to absorb water."Disease is killing the frogs, but climate change is pulling the trigger," Dr. Pounds said. "Global warming is wreaking havoc on amphibians, and will cause staggering losses of biodiversity if we don't do something fast."
