A is for Axolotl

Imagine a creature that never grows up, can regenerate limbs without scars, and has a sort of slimy, alien-like cuteness.  Sounds like a critter you’d like to meet, right?  Ambystoma mexicanum, the axolotl, lives all over the world in aquaria but their only wild habitat is under severe threat.  Chances are that neither of us will ever meet a wild one and that is a shame.

This fascinating amphibian, through a quirk of evolution, is neotenous.  This means that it never really leaves the tadpole stage.  Where most salamanders and frogs will leave behind external gills and develop lungs to breathe on land, the axolotl decides it is perfectly happy and stays put underwater with beautiful gill fans collecting the oxygen it needs.

Image by Faldrian
This axolotl is a strong, independent amphibian that don’t need no lungs or terrestrial environment.                                                           Image by Faldrian

Not only does this incredible creature never grow up, but it can also totally regenerate lost limbs.  This makes it a valuable model organism for scientists to study in the lab.  The exact mechanism behind this regeneration is still being investigated, in hopes that one day a technique for human regeneration will be discovered, but there are some interesting findings that have already come out.

The generally accepted theory was that when a limb was cut off, the axolotl would send a signal to the stump that would turn the cells at the end to pluripotent stem cells.  These cells would be able to duplicate and grow into any tissue and are similar to the cells found in embryos.  Recent research out of Germany, however, showed that the cells at the end of the stump don’t revert to a totally embryonic state.  They are still able to grow into tissues, but only certain kinds of tissue.  The part of the stump that was muscle remembers that it needs to grow muscle, whereas the part that was nerve remembers that it needs to grow nerve.

Step-by-step limb regeneration.  From the lab of James Monaghan
Step-by-step limb axolotl limb regeneration.      From the lab of James Monaghan

Lake Xochimilco in Mexico City is the only place in the world the axolotl can be found in the wild, making them critically endangered according to the IUCN.  They used to live in another nearby lake named Chalco, until that was drained for fear of flooding.  For hundreds of years the axolotl was abundant enough to be a staple in the diet of locals, but now they are nearly impossible to find.  In a 2002-2003 survey where over 1800 nets were cast over the entirety of Lake Xochimilco, scientists could only find 42 of the little amphibians.  The first thing to understand about axolotl decline is that calling Xochimilco a lake is kind of a stretch.

"Lake" Xochimilco.  Basically a network of canals surrounded by farms.
“Lake” Xochimilco. Basically a network of canals surrounded by farms.

This small, restricted environment is a closed system, meaning it does not drain anywhere.  It is also surrounded by farms which provide much of the food needed to feed Mexico City.  Agricultural runoff from the farms and pollution from the nearby megacity accumulate, causing severe damage to the ecosystem and endangering the few axolotls that remain.

The axolotl is an incredible animal at severe risk of extinction in the wild.  It is the Peter Pan of the animal kingdom, refusing to grow up and hiding from hooks.  It’s most amazing power, regeneration, is still being studied and one day may prove the key to human limb regrowth.  For all this and more, the axolotl is most definitely an interesting thing.

Some captive axolotls, like this one, are leucistic (a condition similar to albinism that causes animals to become white).  Aren't they cute? Image by Henry Mühlpfordt
Some captive axolotls, like this one, are leucistic (a condition similar to albinism that causes animals to become white). Aren’t they cute?
Image by Henry Mühlpfordt

For more information on this beautiful creature, follow the links below

Weird Creatures with Nick Baker did a great documentary on axolotls which is available on Youtube.

The IUCN has put the axolotl on its red list of endangered animals

The German team who study axolotl limb regeneration

One Reply to “A is for Axolotl”

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