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  • High up in California Sierra Nevada Mountains near snowpack-filled lakes, there lives one

  • of the greatest threats to biodiversity in human history.

  • That threat is a recently discovered

  • fungus and its victims are these guys. Yes frogs. In this case, the extremely rare yellow

  • legged frog. These elusive amphibians have lost over 80% of their population, due to

  • an extremely deadly fungal infection. And they aren't the only species at risk, the frogs

  • are part of a larger global amphibian crisis that is brought 32% of all the known species

  • of frogs, salamanders and caecilians to the brink of extinction in no small part due to

  • this fungus.

  • This loss of biodiversity threatens to have a wide ranging impact from disrupting habitats,

  • to preventing the advancement of medical research.

  • Now, scientists are heading out to the mountains, in an effort to save

  • this important species before it's too late.

  • When we talk about that mountain yellow legged frogs were really talking about two

  • species, Rana muscosa which is the southern species and Rana sierrae,

  • which is the northern species that occurs north of Mather Pass.

  • Both species are very closely related, and they both live

  • in very high alpine lakes, usually above 8,000 feet.

  • These unique frogs weren't always rare. In fact, their numbers were abundant before

  • more people began to settle around the Sierra Nevada Mountains in the late 1800s.

  • There are reports of people in the early 1920s, you know, not being able to walk through a

  • meadow without stepping on a frog.

  • Those same settlers led to the initial decline of the frog population.

  • In order to attract tourists and fishermen, they brought non native fish species to the

  • Sierra, specifically trout. Trout happened to feed on tadpoles and young frogs.

  • So, unsurprisingly, the amount of frogs in the Sierra quickly plummeted when they arrived,

  • The fish started being removed in the 1990s, and that did lead to a rebound,

  • but a far greater threat was on the horizon.

  • Unfortunately, not very long after that is when the fungal disease chytridiomycosis

  • comes into the Sierra Nevadas.

  • Chytridiomycosis is caused by the fungus batrachochytrium dendrobatidis.

  • We sometimes just call it BD for short,

  • sometimes we just call it chytrid. It was only first written about in 1998. So, there's

  • still a lot we don't know about this disease, but its discovery has been a huge breakthrough

  • and understanding why amphibian populations have been declining so rapidly.

  • And, unfortunately, it also has

  • somehow spread. Literally throughout the world.

  • So on every continent where frogs exist, chytridiomycosis also exists.

  • It's responsible for a third of the world's amphibians becoming threatened.

  • We already believe that about 100 species have gone extinct because of chytridiomycosis.

  • Of course there are other factors that are affecting amphibian populations like

  • habitat loss, invasive species and climate change, but chytrid is recognized as a major

  • factor, and its lethal effects can be attributed to the unique way that a frog can breathe.

  • The frogs osmoregulate through their skin which just means that their skin is permeable

  • and water and gases can really kind of pass through the skin. Frogs can stay underwater

  • for a very long period of time because they can absorb oxygen, through their skin that

  • way. Unfortunately, it also means they can absorb fungal spores, and those fungal spores

  • that they're when their body reacts to it. What it does is it tries to slough off that

  • infected skin, and it's impossible for them to slough off enough to get rid of

  • it, and eventually what happens is they die of heart failure.

  • So once the fungus is present in the water. There's really no way for the frogs to get

  • around it.

  • I think what makes it so difficult is that it's so ubiquitous just in the water supply.

  • You know how do you treat the entire range of the Sierra Nevada Mountains?

  • Since treating native habitat is out. That means the frogs must be inoculated back at

  • the lab at the Oakland Zoo. Fortunately, the researchers here have a plan to treat and

  • release their yellow legged patients back into the wild. And the solution starts by

  • getting to the frogs early before they're technically frogs at all

  • Chytridiomycosis is really just affects the keratin on the frog. Keratin is, you know,

  • a human it's like your fingernails or your hair that kind of thing but on frogs their

  • their keratin their keratinized skin is really in that webbing between their toes and on

  • the inside of their thighs. It's where the skin is more permeable. As tadpoles, the only

  • keratinized part of the body is the mouthparts.

  • And so it doesn't seem to have a major effect on tadpoles.

  • But just getting a hold of some tadpoles is an ordeal, because of the frogs' remote

  • habitat, a helicopter trip courtesy of a partnership with the California Department of

  • Fish & Wildlife is needed to retrieve the healthy tadpoles from their mountainous

  • dwelling.

  • Once in the lab, Rousser's team will raise the frogs under optimal conditions,

  • until they're ready for a high tech upgrade.

  • Our goal is to bring them up to a size of 40 millimeters measured from their tip of

  • their snout to the tip of their back end, it's called the snout vent length. And the

  • reason for that is because then we can implant them with a microchip. So basically,

  • frog cyborgs, it's just

  • like the microchip that you would use for your dog or cat, that allows us then to track

  • those frogs over the long term after they've been released. Okay, maybe not

  • full on cyborgs, but the implanted microchip does allow the California Department of Fish

  • and Wildlife to scan the frogs and track them for several years after being released into

  • the wild. Once they're fully formed and ready, the frogs are intentionally exposed to the

  • fungus, which is done under close supervision of course.

  • We actually test them every single week we treat them at about three weeks, or when they

  • reach 600,000 copies of the critical infection intensity. So ideally we want them

  • to develop a moderate level of infection, allow their immune systems to kick in and

  • then we treat them. And then that way when they go back to the wild and they're released.

  • They may get a moderate level of the infection, but they're never going to get so

  • sick that it's going to kill them

  • After the frogs have been microchipped, treated, observed and have built up an

  • immunity to chytrid, it's back to the helicopter for return to their home in the mountains.

  • It may seem like a lot of work for a small group of rare frogs.

  • But amphibians are much more important to people than may be readily apparent.

  • Not everybody notices their inherent beauty and worth what I usually say to people is

  • well. How do you feel about mosquito-borne illnesses? There are a lot of problems that

  • can be caused by mosquitoes and frogs eat mosquitoes.

  • The other thing is that tomorrow's medicines may come from frogs.

  • In addition to being vital to medical research and saving us from mosquito-borne illnesses,

  • which honestly already seems like enough.

  • Frogs can also tell us about how healthy our ecosystem is and what

  • dangers might be right around the corner.

  • Frogs are considered an indicator species, which means that because they are very

  • sensitive and absorb through their skin, they're going to be the first thing to react to

  • some sort of pollutants or chemical in your system, and because they're amphibians,

  • they can alert you to problems on water and on land.

High up in California Sierra Nevada Mountains near snowpack-filled lakes, there lives one

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B1 frog fungus sierra skin fungal microchip

This Frog-Killing Fungus Could Wipe Out Entire Species

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    林宜悉 posted on 2020/11/17
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