In California’s Sierra Nevada mountains,
yellow-legged frogs survive at some of the
highest elevations of any amphibians in North
America.
As with all frogs, their skin is essential.
On a hot day, they drink water through it.
And they absorb the sodium and potassium their
hearts need to work.
When they’re at the bottom of a lake -- which
is where they spend the winter -- they breathe
through their skin.
And those black dots ooze mucus that protects the skin from infection.
But it doesn’t always work.
In the late 1970s, a fungus started getting
into the frogs through their skin,
moving through the water, or passed on by other frogs.
Those tiny transparent beads you see moving under the microscope
are spores of chytrid fungus.
The spores burrow down into the frog’s skin.
The skin gets irritated.
Then it sloughs off.
It can no longer absorb sodium and potassium.
Eventually the frog dies.
Chytrid fungus has been like the “black
death” for amphibians.
It has decimated some 200 species around the
world.
In the Sierra, chytrid fungus swept across
the mountains and in three decades killed
almost every single yellow-legged frog.
So scientists did an experiment to see if
they could save the species.
They grew some frogs from eggs.
Then they infected them with chytrid fungus.
This was risky.
But they hoped to give the frogs something
like a vaccine.
The original experiment took place at the
University of California, Santa Barbara.
Now it’s being replicated at the San Francisco
Zoo.
The frogs got sick.
Their skin came off.
But then researchers treated the frogs with
a liquid antifungal that stopped the chytrid
before it could kill the frogs.
When the frogs were nice and healthy again,
researchers re-infected them
with chytrid fungus.
To their surprise, the Santa Barbara scientists
found that all the frogs they had immunized
survived.
Every one of them.
Now the San Francisco Zoo has immunized 124
mountain yellow-legged frogs.
And they’re returning them to their mountain lakes.
[WOMAN: "There you go!"]
The idea is that next time chytrid fungus ravages
the lakes, as it inevitably will, these frogs
will have immunity.
Some will survive.
They’ll get a chance to reproduce, and maybe,
slowly, a more robust population of frogs
will once again thrive here in the alpine
lakes of the sierras.
Oh good, you’re still here.
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