Axolotls: The salamanders that snack on each other (but don't die) - Luis Zambrano
In 1864, French zoologist August Duméril
was baffled while investigating
the axolotl.
Unlike many other amphibians,
which transform into terrestrial adults,
axolotls retain their juvenile
characteristics and never leave the water.
In an attempt to induce metamorphosis,
Duméril spent months removing their gills.
But in most instances, the axolotls
simply... grew them back.
Indeed, axolotls are masters
of regeneration:
they can flawlessly regenerate body parts
ranging from amputated limbs and crushed
spines to parts of their eyes and brains.
So how do they do it?
And what other secrets are they keeping?
This extraordinary salamander is native
to the wetlands in Mexico City.
Ancient Aztec people considered it
the incarnation of a God named Xolotl—
hence the axolotl’s name,
roughly meaning “water monster.”
Axolotls reach sexual maturity with gills
and a tadpole-like dorsal fin.
Scientists think their forever-young
condition, called “neoteny,”
evolved because of their stable habitat.
For salamanders that develop in waters
that dry up,
efficiently transitioning to land
is essential.
But the lakes axolotls evolved
in were unchanging year-round
and didn't host many aquatic predators.
So, scientists think it was advantageous
for axolotls
to forgo the demands of metamorphosis.
However,
they haven’t completely lost this ability.
If exposed to certain substances,
axolotls will turn into adults.
But they’ll often experience
shorter lifespans
and lose some of their self-healing
abilities.
These regenerative talents may seem like
crazy superpowers to begin with,
but axolotls have good use for them.
As babies, they’re in direct competition.
So, they snack on each other.
This is usually not a huge problem
thanks to how quickly
they can regenerate body parts.
When an axolotl loses a limb, tissues
stimulate growth in the area.
Skin cells divide and cover the wound.
Then, progenitor cells, which can develop
into various bodily tissues,
form a mass at the site of injury
and nearby nerves secrete
growth-promoting proteins.
Over the next few weeks,
a new limb emerges
as cells proliferate and differentiate
in coordination.
This process could potentially lead to
uncontrolled growth and tumor formation.
But axolotls are remarkably
resistant to cancer.
They have a system in place that tightly
controls cellular proliferation.
To better understand the axolotl’s
baffling biology,
scientists sequenced its genome.
They found it to be more than ten times
longer than a human’s.
Mutations can change the length
of any animal’s genome.
For whatever reason, salamanders have
much more DNA than other vertebrates
because they lose parts
of it less frequently.
Investigating the axolotl’s genome,
scientists saw many repeated sequences,
most of which don't code for proteins
and have no known function.
They also found genes
that are key in regeneration.
However, the biggest factor that sets
axolotl regeneration apart
may not be a set of unique genes,
but how they regulate their genes.
It’s no wonder that axolotls are one
of science’s most studied animals.
But their population in the wild
has plummeted.
Hundreds of years ago, axolotls thrived
under the Aztec capital.
Within the surrounding lakes,
Aztec people built islands called
chinampas for growing crops.
This highly productive form of agriculture
created a vast system of canals,
expanding the lake system’s
shallow, sheltered habitat—
the axolotls’ ideal environment.
But when Spanish invaders arrived,
they began draining the lakes.
And even more water has been
diverted in recent years.
Today, the entire population of wild
axolotls is found in just one place,
Lake Xochimilco, where it’s threatened
by pollution and invasive fishes.
People are working to regenerate
the ecosystem
and strengthen the 2,000 year old
chinampa farming tradition.
If interest grows, farmers could recover
abandoned chinampas
and support the local community—
along with the axolotl.
Eventually, the benefits of saving
this salamander might be even greater.
Scientists hope that one day
we’ll be able to apply
the axolotl’s masterful tumor suppression
and regenerative abilities
to the human body.
Perhaps its secrets are the real reason
for the slimy god monster’s smile.
