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.