It can grow a new head even if it's missing! Why is the "Axolotl" so amazing?

If you love to visit flower and bird markets, you may have seen this creature with "superpowers". People like to call it "Axolotl". It has a cute face, six pink "tentacles", a white body that floats up and down, and four short hands that scratch around.

So is it the prototype of Shenlong or the descendant of dinosaurs? Well...neither.

Image source: Pixabay

Its scientific name is Ambystoma mexicanum, an amphibian native to Mexico. It is also known as the American axolotl. It is listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), so strictly speaking, even if its artificial species can be seen everywhere in the flower and bird market, it is not an absolutely standardized thing.

Axolotl is a popular trade name for it in the market. This name can be said to completely avoid the essence of the Mexican axolotl. First of all, the Mexican axolotl is not a dinosaur. We know that dinosaurs are a type of saurischia in the Mesozoic era. Except for the descendants of birds, they are all extinct. They are reptiles and have nothing to do with amphibians. Secondly, its hexagons are not horns. The three pairs of feathery gills on its head are used for breathing in water.

#1 Life is all about eating and drinking

It is not difficult to see from the not very smart eyes of the axolotl that it has no special needs except eating, drinking and reproduction. For suspended food, they can use the negative pressure in their bodies to push the water flow to eat.

Perhaps because they live underwater, they have a large appetite and, like many amphibians, they are unrestrained and regard eating as a stereotyped action and a life creed. They eat all kinds of moving insects, small fish, tadpoles, and their own kind that they can beat - yes, sometimes when they see their companions' external gills growing and their limbs extending, they will smack their mouths. If they are raised in captivity and in a closed environment, this phenomenon will occur more frequently.

#2 I don't want to grow up

Since the Mexican axolotl is also an amphibian, it should also undergo a metamorphosis process, just like a tadpole grows into a frog, but it doesn't do that. It's so good underwater, why don't we go up there! Stop working hard and start playing badly.

Its metamorphosis is extremely incomplete. When it is young, it looks like a normal tadpole. When it grows up, it never goes ashore and does not like to breathe with its lungs. Its most obvious feature is that its six feathery gills simply do not degenerate and are used well. It is truly the king of bathing.

This seemingly immature characteristic is called "neotyping" in biology. It refers to the asynchronous development phenomenon of some species, in which certain characteristics of their infancy or even embryonic stage will be retained until sexual maturity, the reproductive period, and even until death without major changes.

Of course, this neoteny is also reflected in the face, which has this cute face from childhood to adulthood. Humans are naturally fond of species with neoteny features and think they are cute, but the Mexican axolotl looks like this, it really is not smiling at you on purpose!

Image source: Pixabay

#3 You can make art out of me, but you don’t have to

Regardless, most of us are interested in the axolotl because of its innocent appearance. However! The most classic white axolotl we see is actually the albino (lack of melanin, so it has white skin and red eyes) or leucistic (lack of any pigment in the skin, so it has white skin and black eyes) of the Mexican axolotl.

The wild axolotl looks just like it originally does, it is a small black fat man with scabies and pockmarks. There is no other way, to protect itself in the water, it has to keep a low profile and cover itself with a skin that looks like a bottom layer of black mud.

As the saying goes, "technology is based on changing skin", the Mexican axolotl cannot escape the fate of becoming a creative material for humans. In addition to turning white, there are now golden albino species, which are golden yellow all over; black species, which are as black as ink. This is not all, these species may also grow stripes when they grow up, such as albino species will grow golden stripes, while white mutants will grow black stripes.

When humans saw the mixed colors, they immediately flocked to the striped varieties, just like the idea of ​​koi. What's more, if the fluorescent protein gene is transferred into the body of the axolotl, it will emit night light in the dark.

Don't be surprised. In the flower and bird market, fluorescent zebrafish and axolotls are no longer rare species. The legality of this technology has not been fully discussed in China. This technology was originally used in laboratories to facilitate scientists to observe experimental results, such as studying the super regenerative ability of Mexican axolotls.

#4 Oh, it's just a fatal injury

This brings us to a feature that mammals don't understand and birds don't understand - the Mexican axolotl has an extremely magical ability to recover its limbs. We know that some reptiles, represented by geckos, have the characteristic of "self-amputation", that is, a behavior of actively cutting off their tails to seek survival. However, the tails they develop again are just a fake one, without a formed coccygeal vertebrae, and are supported by cartilage tissue.

The Mexican axolotl has a much higher regenerative ability than reptiles, and it can even regenerate its own limbs. For example, if a dinosaur had a limb bitten off by its companion, its wound would not heal itself in the form of a scar, but would grow a fully functional new claw within a few months. Some cases show that they can even repair injured spinal cords and parts of the brain, and can easily accept brain tissue transplants from the outside.

In the laboratory, we can observe the entire process of limb regeneration by tracking fluorescent proteins. It turns out that after its limb is amputated, the cells at the wound will form a series of unipotent stem cells, just like the mature tissue "degenerating" and returning to an undifferentiated state, with extremely strong "plasticity". These stem cells gather into "blastema" tissue, and then slowly differentiate into different types of cells such as skin, muscle, nerve, etc., and finally grow a limb that is the same as the original one.

Such proficiency in the use of stem cells is something that even humans can only dream of. Therefore, there is a special discipline called "regenerative medicine" in medicine, which studies limb regeneration technology with stem cell technology as the core. The Mexican axolotl is really a perfect model organism.

#5You can never go back to your hometown

The Mexican axolotl is so useful, but its own living space is in danger. In the wild, the Mexican axolotl only lives in a small area of ​​Mexico, and its population is gradually becoming scarce. It has become a fact that it has entered the ranks of endangered species.

The artificially bred axolotls you can buy in the flower and bird market can no longer be released into the wild, which means it is extremely difficult to return them to replenish the wild population. The reason is probably because the genes of the artificial species have shown a kind of "involution". They seem colorful, but in fact they are highly inbred - just like koi, which have no value for release into the wild. The only thing to be optimistic about is that axolotls enthusiasts around the world are concentrating on studying these artificial species, and the black and ugly wild Mexican axolotls can be reduced from being overfished.

Source: Chongqing Science and Technology Museum

Author: Anhao, a graduate student in biology and a dual-author of popular science and science fiction.

Review experts: Huang He, Li Chunli, Chen Tao, Xu Xiaoping

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