Frogs on the Brink of Extinction
Deadly fungus linked to old pregnancy tests is systematically killing the world's amphibians
St. Louis Post-Dispatch
By Jeffrey Bonner, President of the Saint Louis Zoo
April 6, 2008
In the fourth of a monthly series this year, Saint Louis Zoo President Jeffrey Bonner explores a part of the globe where the Zoo is working to conserve threatened species, protect natural habitat and partner with other organizations to strengthen the web of life in which we all live. See this story in St. Louis Post-Dispatch.
Throughout the 1940s and 1950s, doctors throughout Europe, Australasia and America relied on a single frog species to determine whether a woman was pregnant. The African clawed frog, harvested from the wild in Africa and exported all over the world, was preferred because both males and females could be used in the tests.
But this amphibious workhorse carried a dark secret - a disease called amphibian chytrid. Clawed frogs developed immunity, but the disease became lethal to virtually all other forms of amphibian life. Because of the pregnancy tests, the fungus was transmitted by water into sewers worldwide. The disease is now found on all six continents that have amphibian life and is systematically killing the frogs and toads, salamanders and newts that live there.
Amphibian chytrid can only be detected through genetic testing. It moves slowly, advancing only 15 or 20 miles a year, and can't survive long outside of water. But it is a vicious killer, most lethal at higher elevations and cooler temperatures, and can deplete 85 percent of the animals in a stream. Those spared are too scattered to reproduce, and so entire species slide inevitably toward extinction.
We know of about 6,000 species of amphibians. One-third to one-half of the world's frog species is likely to go extinct in our lifetime, researchers say. Amphibians have lived on our planet since before the age of dinosaurs - at least 360 million years. Since the end of the dinosaurs, no class of animals has suffered such a massive and swift decline.
We do not know exactly what this loss will mean. Frogs and other amphibians are both predators and prey. They provide food for animals like birds and fish, but they also eat insects. Insects, of course, can have a profound effect on food production and disease transmission, which, in turn, could have a profound effect on us.
The loss of so many species could also be significant in other ways. Frogs are like sponges. They absorb oxygen and moisture through their skin. They have had to develop defenses against bacteria and viruses that humans don't have. Frogs have remarkable recovery powers because they secrete an antimicrobial compound that disinfects everything it comes into contact with.
The secretion contains a peptide, one of a family of small proteins that can kill bacteria by rupturing their cell membranes. This peptide could have almost limitless applications in human medicine. The famous poison dart frogs of the rainforest secrete a chemical called epibatidine. Already this compound has shown promise as a new, non-narcotic but extraordinarily strong pain reliever.
What we don't know about frogs and human medicine is even more astounding. The best example comes from Australia's gastric brooding frogs, discovered in 1973. The frogs give birth by swallowing the fertilized eggs and allowing the tadpoles to develop in their stomachs. Somehow the gastric juices are shut down, allowing the babies to mature unharmed. To give birth, Mom just opened her mouth and out popped a perfectly formed froglet. At the very least, the gastric brooders held the promise of curing something like common ulcers. Perhaps they held the cure to obesity and the physical problems that go along with it. Sadly, we'll never know.
In the spring of 1980, the chief ranger of the Queensland Parks and Wildlife Service discovered that the gastric brooders had not returned to their breeding grounds. They had become extinct almost overnight. Because none were kept in captivity, their secrets disappeared with them.
Saving the Frogs
Of the 2,000 to 3,000 species of frogs in trouble, 500 species are on the critically endangered list. These are the species that we need to bring into conservation breeding programs immediately if they are to avoid extinction.
About three-quarters of these live in the Americas, from the northern border of Mexico south through Central and South America. People tend to think of frog habitat as low, swampy areas, but that's not really true. Mountainous regions, the perfect environment for amphibian chytrid, are rich in frog species. Ecuador, a country dominated by the Andes Mountains, has the third largest number of amphibian species in the world.
It is relatively simple to find frogs and keep them healthy. Frogs already infected with chytrid are relatively simple to cure if the disease hasn't progressed too far. We can't put them back into the environment, as they'd just get re-infected. Zoos, aquariums and other biosecure facilities can save about 500 species for the short term until their native habitat is once again safe.
That's why the World Association of Zoos and Aquariums, in conjunction with the World Conservation Union, has declared 2008 "The Year of the Frog." For the first time in history, all the world's zoos and aquariums have agreed to focus on the problem of amphibian extinction to raise awareness and interest in frog conservation on the part of governments, world media, educators and, of course, the general public.
Several years ago, I attended a seminar in Washington. It was spring - cherry blossom time. I was sneezing like crazy. Our speaker also had allergies, and he apologized for his sniffles. Being a biologist, he explained it this way, "Sorry for all the sneezing. It seems I've become an inadvertent participant in the sex life of trees." He was right, of course. We sneeze because we have an immune reaction to the pollen, or sex cells, which trees spread in the spring.
If frogs could speak, perhaps they'd say the same thing about amphibian chytrid. It would have taken forever for chytrid to spread out of South Africa had it not been for the actions of humans, harvesting infected frogs and air-mailing them around the planet for pregnancy tests. The frogs, it would seem, were an inadvertent participant in the sex lives of humans.
We can allow hundreds of amphibian species to face quietly into oblivion, or we can take action now to spare their lives. I hope the choice we make is the humane one.
• About 50 percent of the known 6,000 amphibian species are threatened with extinction. The great majority would be frogs and toads.
• About one-third of them are known to be threatened, and an additional 23 percent are "data deficient" but believed to be threatened.
• 165 species of amphibians have already gone extinct.
• The Amphibian Ark project at the St. Louis Zoo will identify the 500 most endangered amphibian species and help establish breeding programs across the globe.
Source: Saint Louis Zoo
• Amphibian Ark - www.amphibianark.org - is a worldwide effort to save frogs, toads, salamanders and newts.
Jeffrey Bonner is president of the Saint Louis Zoo. He also is the chairman of the Amphibian Ark, the global effort to save 500 critically endangered species and place them in "protective custody" in zoos and aquariums around the world.
Republished with the permission of the St. Louis Post-Dispatch
Copyright 2008 St. Louis Post-Dispatch
Courtesy of STLtoday.com