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Saving Frogs from a Global Enemy
2/17/2007 Weekend All Things Considered (NPR) By Debbie Elliott
DEBBIE ELLIOTT, host:
Now that you're letting your imagination play, think about this scenario. A mysterious fungus is floating in the air around you. As you breathe in, the fungus settles in your lungs and starts to spread. It becomes harder and harder and then impossible for you to breathe.
Others catch the disease, then dogs, cats, horses. Eventually all mammals could be wiped out. This week on Science Out of the Box, we ask what would scientists do to prevent a mass extinction?
Okay, so there isn't a fungus in the room with you threatening to coat your lungs. But there is a fungus that's threatening to kill the world's frogs and possibly spread to other amphibians.
Scientists met in Atlanta this week to try to stop this. Among them was a group that runs a program called Amphibian Ark. It aims to give the creatures refuge from the deadly fungus. Dr. Joe Mendelson is with the group. He's a herpetologist, a reptile and amphibian scientist at the Atlanta Zoo.
Dr. Mendelson joined us from the zoo's frog room. To give us a sense of how the place sounds at night, he played a tape of the frogs in his care as he described his lab.
Dr. JOE MENDELSON (Herpetologist): I'm looking at whole lines of aquariums with native plants in them and waterfalls and things like this, of amphibians that cannot be safeguarded in the wild. And so unfortunately we have no choice than to keep them alive in captivity.
ELLIOTT: Something like froggy quarantine?
Dr. MENDELSON: Yeah.
ELLIOTT: Let's talk a little bit about this fungus. What is it and how does it kill frogs?
Dr. MENDELSON: We only discovered this fungus in 1998. It's microscopic, so it's very difficult to see, and it has the capacity in some cases to move across landscapes and remove all or most of the amphibians in an ecosystem.
ELLIOTT: What does it do to them?
Dr. MENDELSON: As best we know, it gets in their skin, little microscopic fungal bodies, and digests literally the protein called keratin, which is the water-proofing protein in their skin. And they lose the ability to exchange gases through their skin properly and to maintain their water balance properly.
ELLIOTT: Is there any idea where it came from?
Dr. MENDELSON: There is some indication that this fungus was a typically (unintelligible) fungal disease with some amphibians in Africa, particularly the African (unintelligible) frog, which was widely distributed for pregnancy tests and other laboratory studies in the last century.
ELLIOTT: Pregnancy tests? How did that work?
Dr. MENDELSON: Well, if the urine of a pregnant woman is injected into this frog, the female frog, she will lay eggs.
ELLIOTT: So these frogs were exported from Africa all over the country to be used in hospitals?
Dr. MENDELSON: All over the world to be used in hospitals and also in basic physiology labs at universities. And there's an indication that they carried the fungus with them and that it slowly got itself into natural landscapes on every continent. It's now known on every continent, but we don't know the extent to its effect on every continent, because it's very difficult to track a microscopic fungus in an environment as complex as a rainforest.
ELLIOTT: Now, how bad could it get? What is the worst case scenario here?
Dr. MENDELSON: There's a little over 6,000 species of amphibians in the world and our minimum estimate is that about a third of those are in imminent risk of extinction. That's 2,000 species at risk of extinction simultaneously. That's why this qualifies as a mass extinction event on the scale of what happened at the end of the ice ages with mammoths and mastadons. And that's why it's equivalent to what we know from the fossil record happened in the case of the dinosaurs.
ELLIOTT: So this would be something that humans had never witnessed before should there be an extinction of this scale.
Dr. MENDELSON: Without a doubt, there's no precedent to an extinction at this scale in human history.
ELLIOTT: Now, how do scientists know that the fungus is to blame for these frogs dying off and that it's not some other factors?
Dr. MENDELSON: We don't claim that the fungus is the only thing to blame. There's no doubt in anyone's mind that amphibians are indeed suffering what we call death from a thousand cuts. Habitat loss, chemical pollution certainly has its role. Climate change - even though it's very difficult to really demonstrate its exactly to amphibian declines - certainly has a role. And this fungal disease is yet another layer on top of that.
ELLIOTT: Now, remind us all of just what it would mean in the world if one third of the amphibian species were wiped off the planet?
Dr. MENDELSON: Amphibians function as the ecological middle men, so to speak, because they are both predators and prey, connecting in that sense hyper-abundant insects with predators above them. And they exist in densities in ecosystems that are far and above all other vertebrates combined. And these include frogs, toads, salamanders, newts, and these strange tropical creatures called caecilians.
ELLIOTT: Caecilians, what are those?
Dr. MENDELSON: Caecilians. Caecilians look like gigantic earthworms, and by gigantic I mean perhaps up to four, five feet long. And they're limbless, they're eyeless, and they burrow around in the leaf litter and mud of tropical rainforests.
ELLIOTT: Is there a sense of how this would affect humans should this fungus wipe out one third of amphibians?
Dr. MENDELSON: Realize the precedent that amphibians are setting here. A disease that we did not know existed and we don't know from where it came and we don't know how it gets around, it's working its way across an entire vertebrate class, eliminating species in an incredibly accelerated pace. And we can't stop it.
ELLIOTT: Dr. Joe Mendelson is an organizer of Amphibian Ark. Thank you.
Dr. MENDELSON: You're welcome.
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