Amphibians are being compared to dinosaurs more and more often. Not only because they are both considered to be cold-blooded, but also because they seem to be dying off in the same drastic manner.
The dinosaur didn’t go quietly, or too kindly. Its downfall? Probably a meteorite the size of Mount Everest. Its impact created enough dust to block the sun’s rays from the Earth’s surface. This prevented plants from growing, which led to the starvation of herbivores. And when their food source failed to reproduce, the omnivores and carnivores suffered the same fate. An estimated three quarters of all species died.
But it seems that it doesn’t necessarily take a rock falling from the sky to cause the devastation of a species. A group of people suspect that something similar is happening – a real mass extinction, which is what palaeontologists call the loss of more than three quarters of a species in a few millions.
The first casualties of this modern day extinction seem to be amphibians; frogs, toads and salamanders appear doomed because of a life-threatening mould. Well, scientists think it’s the mould..
Alarm bells sound
At least a third of more than 6,000 types of amphibians are threatened, according to the International Union for the Conservation of Nature (IUCN).
The figure is fuelled by ominous stories about field researchers who met with apocalyptic scenes of countless dead frogs. Or of biologists who’ve walked through frighteningly quiet forests. “I have been in the cloud forests of Costa Rica,” says Frank Pasmans, Professor of Veterinary Bacteriology and Mycology at the University of Gent (Belgium), “and the forests there are really empty. You almost don’t see any amphibians.” How is this possible? A mould with an unpronounceable name, Batrachochytrium dendrobatidis (Bd for short), creates victims. It causes the disease chytridiomycose and leads to degradation of the keratins in the skin of the amphibians. Diseases in the animal kingdom are a dime a dozen, so what makes this one so special?
“Normally a disease has an effect on a limited type of species,” says Pasmans. “This mould infects many different types of amphibians.”
Even more remarkable is its impact. There are usually a few individuals in a population who survive an epidemic, and there are always a few individuals immune to the disease. “This is a unique scenario because the mould seems to wipe out whole species,” he says.
• Mould is everywhere
Bd doesn’t only take its victims in the forests of Middle-America. It has also wrought havoc in Australia and Spain. And Pasmans has the dubious honour of documenting the first casualty in Belgium. But whether one dead Midwife Toad means a large-scale outbreak of the deadly chytridiomycose remains to be seen. “We have not seen a massive number of deaths as a result of Bd yet,” says Annemarieke Spitzen, project leader at RAVON (Reptiles Amphibian Fish Research Netherlands).
It is, however, clear that the mould has spread to northern Europe: from research in 2009 it seemed that 4% of amphibians are infected. “It could be that our amphibians are less sensitive, but it could also be that we can’t see the damage yet,” according to Spitzen. If the mould takes its victims during the metamorphose from tadpole to adult animal, it would happen in the water.
It could also be that this variety of Bd is not the same as the dangerous mould that is killing amphibians elsewhere. “We don’t know if the virulent print is found here,” says Pasmans. “So we don’t know if the dead toad, which died from the disease, is going to be one of many.”
• Man spreads disease
Where and when the next victims will show up is unclear. The roots of the disease are also uncertain. It looks like the mould has had help from mankind. Suspicions are that the African Clawed Frog has something to do with it. They were once used for pregnancy tests… and they are very cute in an aquarium. There was a lively trade in these animals. It could be that these frogs spread the mould all over the world. And all our dragging around of the amphibians could have given various species the opportunity to develop a very virulent variety. In the meantime, Bd is spreading from one puddle to the next ditch without our help. How this happens is unclear.
“Water birds could play a part,” says Pasmans. What is clear is that the spread of the mould is unstoppable.
“In reality it is quite a simple organism,” says Pasmans. “It is not equipped against draught, high temperatures and disinfecting products.” The mould feels most at home on amphibians: they are the perfect habitat. “They keep a constant temperature and a high humidity,” he says.
• Save the frogs
Is it now high time that we spread a fungicide over the world via an airplane? “Far too drastic,” thinks Pasmans. “Most moulds in the environment are necessary; they decompose foliage on the ground. You could cause a lot of damage if you eliminate them all.” No biologist would therefore condone this action. But, “individual animals are curable,” says Spitzen. “Hobbyists are doing this.” Where animals die, there are people willing to save them. There are biologists and animal lovers -especially in the rain forests of Middle America -catching frogs before they die from chytridiomycose. It is possible to prevent a mould infection with captive amphibians. And a species can survive in captivity with human aid. It seems that, for example, the Panamanian Gold Frog (Atelopus zeteki) has become extinct in the wild. But the little yellow frog is surviving in a number of zoos. The same goes for other endangered amphibians. And it is hoped that they can one day be released back into nature again.
The question is, of course, whether the re-introduction of these animals puts them at risk too. This was apparent from research by the San Francisco State University. Two species of frogs in the Sierra Nevada mountain range, which runs through California and Nevada, were decimated by mould. A third species didn’t seem to suffer from this, but the Pacific Tree Frog was infected. That means that the mould can take its time and wait until vulnerable species are released again, before it strikes.
• How bad is that?
Has the fate of the frog and the salamander been sealed? And how bad would that be? Mass reduction of the frog population could have unpleasant results. “The export of frog legs used to be prohibited in India, because the number of mosquitoes exploded,” says Pasmans.
But maybe we should see the disease as a symptom of something bigger. “We see in Middle America that first the amphibians and then the numbers of reptiles decrease,” says the professor. “Amphibians are indication species,” says Spitzen. “When things go wrong with the frog and salamander then we have a problem with the environment. They are sensitive little animals. They have a water porous skin and that makes them very sensitive to pollution.” Maybe the big bad mould makes clever use of the space that humans gave to it. The IUCN has called the mould disease ‘the worst infection disease for vertebrate animals’. The same organisation rated the most important cause of the decreasing amphibians the loss of habitat. Pollution is the second reason.
• Frogs follow dino
We might not have a clue how to prevent Bd, but how to prevent pollution and destruction in a habitat is, in theory, child’s play. And in practice, other animals will benefit from this as well. Because by destroying the habitat for frogs, one also messes up the habitat for many other animals.
The same goes for the victims of pollution. Before we can talk of mass extinction, more of the 6,000 species of amphibians have to die. But it looks like this is the direction in which we are headed. The dinosaurs were also not the only victims of that falling rock 65 million years ago.
More and more frogs
Amphibians are still being discovered. A Malay researcher announced, in May 2012, the discovery of a new frog, possibly not spotted sooner because it lives under foliage. A proper extensive inventory was made in 1985 to establish how many species are known. It was about 4,000. After that about 2,000 species have been added to the list. Estimates run from about 6,300 to almost 7,000 species. Good news? Not necessarily. Yes, it means those biologists are working hard to map nature. But it could also mean that frogs are dying before ever making it to an official species.
Amphibian tests pregnancy
How do you know if a woman is pregnant? Nowadays we have clever tests at the chemist. They detect the pregnancy hormone hCG in urine. The African Claw Frog used to lend a hand with that. A Claw Frog injected with the urine of a pregnant woman will lay eggs within half a day. This was discovered by British Lancelot Hogben in the 1930s. This frog’s claim to fame comes via the pregnancy test that was used all over the world. Numerous Claw Frogs were exported globally until a better test came onto the market in the ’60s.