How Do Axolotls Work?

These amphibians spend their entire lives in the water and can regrow any part of their body. Learn more about the axolotl in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff, a production of I Heart Radio,
Hey brain Stuff Lauren Vogelbaum. Here in Julio Cortaz's short
story Axelatal, first published in n a Latin American man
living in Paris becomes infatuated with the axeltles living at
the zoo, to the point that he eventually transforms into

(00:23):
one with their quote pink Aztec faces, eyes of gold,
and rosy little bodies translucent, ending in a ficious tale
of extraordinary delicacy. The narrator observes a quote absolute lack
of similarity between axelattles and human beings. In considering these feathery,
pinkish salamanders, he says, it would seem easy, almost obvious,

(00:47):
to fall into mythology. Cortisaar's narrator is, on the face
of things correct in his estimation of the Axelatal for starters,
the Oxelotal fell into mythology centuries ago. According to Aztec legends,
the first Oxelotal appeared in the Lake system around modern
day Mexico City, when the powerful underworld god Zolat transformed

(01:09):
himself into a small, feathery amphibian to escape capture. In
ancient Mesoamerican culture, oxelotals were considered a food source supplied
by Lakes of Jamilico for the good of humanity, and
Courtsar was right about the oxelotals lack of similarity to humans,
Our last common ancestor probably roamed earth around three hundred
and sixty million years ago, and at first or even

(01:32):
fiftieth glance, they're excessively different from us. Among the first
modern zoo animals, thirty four oxelotals were brought from Mexico
to Paris in eighteen sixty four, and although they weren't
as interesting to nineteenth century zoo goers as the larger,
more charismatic animals, scientists quickly realized that these unassuming little

(01:54):
buddies were strange, almost mythological in fact, in the wild,
oxel attles are or at least used to be top
predators in their home ecosystem in the lakes and canals
of central Mexico. They're unusual among amphibians because they remain
underwater for their entire lives, breathing through gills, while most

(02:14):
other salamanders walk around on land and breathe with lungs
during the adult stage of their life. Although they appear
on assuming they're actually ruthless carnivores feasting on worms, mollusks, insects,
and even small fish in the wild, and it turns
out that they have the largest genome of any organism
yet sequenced. Part of the Aztec mythology of the oxelotal

(02:36):
centers around the fact that, like a powerful god, they're
difficult to kill, and that they can regenerate virtually any
part of their body without much problem. While some lizards
can grow back a tail bisected, flatworms can grow back
their other half, and starfish can regrow a limb, an
oxelotal can regrow its heart, afoot a part of its

(02:59):
spinal core, you name it. We spoke with David Gardner,
professor in the School of Biological Sciences at the University
of California, Irvine. He said, of the animals that are
closest to us, the vertebrates, salamanders are the only ones
that can regenerate in this way and can heal without scars.
Other salamanders can regenerate, but oxelotles do it best. When

(03:24):
the Europeans got wind of this, oxelotles went from being
a sort of boring exhibit in the zoo to one
of the most important and the longest self sustaining lab
animals in history. George Couvey, popularly considered the father of paleontology,
studied axelottles in an attempt to figure out whether Carl
Linneus was correct in categorizing the classes Amphibia and reptilia separately.

(03:48):
It was a big question in those days. Covie incorrectly
concluded the oxelotles, because they breathe through gills their entire lives,
must be some sort of lizard that existed as a
perpetual law va, in the words of paleontologists Stephen Jay
Gold quote a sexually mature tadpole. Couvy was correct sometimes,

(04:08):
but not in this case. And because oxeltles did incredibly
well in laboratory and aquarium settings, a nineteenth century zoologist
took it upon himself to provide every lab in Europe
with a supply of them, which resulted in some truly
horrific studies in which scientists chopped them up just to
test the limits of their regenerative powers. Gardner said, these days,

(04:32):
oxyletles are hugely important model systems for our studies about regeneration.
We've known for decades, centuries even that we can remove
parts of a developing embryonic structure and the cells that
are left behind will fill in, repair, and regenerate that structure.
But in most animals and mammals, for instance, the system
sort of shuts down at the end of embryonic development.

(04:55):
Salamanders seem to be able to revert back to that
embryonic like state, re accessing the developmental program that's already there.
Humans have the program, we just stop being able to
access it when we're no longer an embryo. You could say, we,
like oxylottles, have evolved the ability to regenerate just fine,
but we've also evolved a mechanism that inhibits that. Oxeltles

(05:21):
can endure a lot, but they have not been able
to endure their home ecosystem, being overrun with introduced predators
and environmental toxins. The lakes in their home around ultra
urbanized Mexico City have become not only polluted by aging
wastewater systems, but overrun by introduced telapia and perch, both
of which view oxylottles as a delicious snack. Scientists counted

(05:46):
around six thousand oxeltals per square kilometer in Lake Zotomilco,
but these days fewer than thirty five animals take up
the same amount of space. It looks like the oxylottle
is on the fast track to extinction even in their
home environment, which is something of a paradox like the
oxelottle itself. While wild oxelttles are critically endangered, they're doing

(06:09):
great in captivity. They're the most widely distributed amphibian in
the world. Millions of them live in labs around the globe,
many more in fact, than live in the wild now,
and while they're important in science, they're also quite popular
in pet shops. Today's episode was written by Jesslin Shields

(06:31):
and produced by Tyler Clang. For more on this and
lots of other regenerative topics, visit how stuff works dot com.
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