We're here deep in the amazon looking for species on the edge of extinction it's not
a jaguar or a sloth and it's not even a single species but a collection of them
frogs like many of the world's amphibians are being wiped out by the deadliest plague you've
never heard of and if we don't act fast they could be gone for good let's talk about that
except certain salamanders they can extrude sharp venom tipped ribs and two species of frogs with
venom to bones on their skulls amphibians aren't venomous since they don't actively inject their
venom instead they're poisonous since they unload their toxin when eaten by other animals
whereas there are almost no venomous amphibians the world is filled with poisonous ones
there are more than 170 species of poisonous frogs mostly concentrated in south america in the poison
dart frog family named for the native indians they use darts tipped with the frog's poison
to hunt animals for hundreds of years although of those hundred plus species of poisonous dart frogs
only four were ever used to weaponize darts even though the whole family ended up sharing the name
despite their lethality in the wild you can actually get one of these frogs as a pet
and they'd be completely harmless that's because the frogs don't make their own poison
but rather sequester it from what they eat they take up a deadly chemical called a lipophilic
alkaloid from consuming poisonous insects and plants in the rainforest the poison then
accumulates in their bodies and they secrete it through their skin as a defense mechanism against
predators this poison is then absorbed through the victim's skin and prevents their nerves from
transmitting impulses eventually leading to a heart failure as the muscle tissue making up the
heart fails to beat properly and these toxins are incredibly stable so stable that wild frogs can
maintain their lethality for years in captivity away from their natural containing food source
although even without this food source they still maintain their flashy colors the deadliest
of this family is the golden poison frog their dose can vary based on location and local diet
but on average the golden poison frog holds in its little body one milligram of poison now that might
not sound like a lot but that's enough to kill about 10 000 mice and between 10 and 20 humans
the golden frog's exceptional toxicity comes from its extraordinarily rare and lethal poison
but trochatoxin found in only three other poisonous frogs and a handful of other species
the poison attacks the sodium channels in nerve cells these sodium channels are the basis for
electrical activity in nearly all organisms and first appeared in cells about 3 billion years ago
as life propagated outward from those early single celled eukaryotes it carried with it these sodium
channels and now nearly every organism alive uses them from their shared common ancestor they're one
of the few descended traits common across the vast majority of life and since the poison blocks these
channels from functioning it works against most living animals but if a single frog has enough
poison to kill 10 000 mice how is it fine just hopping along well that's because these frogs have
adapted very specialized sodium channels shaped so slightly differently that the poison won't work
but similar enough that the sodium channels still function like normal with these poisonous frogs
and all amphibians for that matter might be coming to an end an infectious disease has been spreading
around the world infecting amphibians and wiping them off the map a fungus named betrachytrium
dendrobaddies was first discovered in the poison dart frog in the late 1990s since then it's been
found on six continents and infected more than 40 percent of all known amphibian species in a
short period of time bd has contributed to the threatened status of more than half the species
it's infected having an even greater impact on the species than human-led deforestation while
humans didn't create pd they've had a huge impact on spreading it it's hard to know exactly where
bd originated but we can get an idea by studying old museum species for the telltale signs of skin
infection so far the oldest known instance is from south africa in the 1930s and geologists think it
may have spread around the world in african clawed frogs which were once used as pregnancy tests
back in 1930 a scientist based in cape town discovered that he could use ox hormones to
control ovulation in a local frog species by 1933 doctors were using the frog to detect
hcg a hormone produced by pregnant women when a pregnant woman peed on the frog it would lay
eggs within 8 to 12 hours the test was both rapid and reliable and so it spread quickly throughout
europe and the united states over the next two decades unfortunately for modern frogs it was much
easier to import these frogs directly from africa rather than growing them domestically allowing the
unknown disease to be spread by physicians around the world vd is the only known fungus of its kind
to infect living vertebrates in amphibians it attacks their skin which they normally
use to breathe and take up water bd interferes with this process suffocating their victims
and infected frogs seem to get froggy delirium they become extremely sluggish often can't write
themselves if turned upside down and will hop around in circles aimlessly all of the handful of
major strains of bd have turned up in amphibians involved in the international commercial trade
showing how the infection continues to be spread today the disease can be traced back at least 90
years but it's been spreading exponentially since and now the situation is becoming increasingly
dire despite not getting any news coverage face it it's almost guaranteed you've never heard of it
it's wiping out frogs left and right the last decade saw three times more amphibian species
go extinct compared to the 90s and the primary cause of extinction in 90 of those species
was bd mortality rates can vary wildly and are highly species dependent but generally speaking a
significant percent of infected amphibians end up dying and some species like the ornate burrowing
frog have a 100 mortality rate when infected many scientists have argued that we're currently in
the sixth mass extinction event fueled almost entirely by humanity's effect on the planet
this claim is backed up by the near 10 000 fold increase in species going extinct we see today
compared to non-mass extinction time periods the result the mass extinction of amphibians which
make up more than 10 of all vertebrates may be slipping by unnoticed the spread of bd also shows
the continued failure of international biosecurity measures to keep bd and other infections contained
one thing's for sure if things continue on their current path we might not have our little green
friends hopping around much longer i hope you enjoyed getting smarter with us today
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