Axolotl facts: the Mexican salamander that keeps growing

Axolotl facts that make this salamander unforgettable

Axolotl facts start with a creature that looks like it never left its larval stage. The axolotl is a species of mole salamander that reaches sexual maturity without undergoing metamorphosis, so adults stay fully aquatic and keep their obvious external gills.

That unusual life pattern has helped make the axolotl one of the most recognizable salamanders in the world of biology. It also has a size range that is easy to picture: a sexually mature adult axolotl can measure from fifteen to forty-five centimetres.

Where axolotls lived in the wild

Axolotls originally inhabited interconnected wetlands and lakes in the highlands of Mexico. Their native population is now limited to Lake Xochimilco.

Wild axolotls were pushed close to extinction by invasive species such as tilapia and carp. The species has been assessed as critically endangered by the International Union for Conservation of Nature.

The wild type axolotl is brown or tan with gold speckles and an olive undertone. In captivity and in breeding lines, the four most common mutant colors are leucistic, xanthic, albinistic, and melanistic.

Why axolotl regeneration stands out

Axolotls do not heal by scarring. Instead, they can regenerate tissue, including body parts such as limbs, gills, and parts of their eyes and brains.

Entire lost appendages, including limbs and tails, can regrow over a period of months. They can also restore parts of their central nervous system, including non-vital parts of their brains.

That regeneration ability is part of what makes the axolotl so remarkable in research and in public imagination. It is one of the few animals known for keeping so many body structures able to come back after injury.

A name with many meanings

The word axolotl has been translated in several different ways, including water slave, water servant, water sprite, water player, water monstrosity, water twin, and water dog.

The name fits a creature tied to water at every stage of life. Even as it becomes sexually mature, it remains aquatic and keeps the external gills that make it look permanently adapted to the water.

The axolotl genome and lifelong growth

The axolotl has indeterminate growth, which means it continues to grow throughout its life. That trait adds to its already unusual biology, because it combines lifelong growth with a body plan that stays juvenile in many visible ways.

Its genome sequence was published in 2018, and it was 32 billion base pairs long. That makes the axolotl a species with a massive genetic blueprint to match its unusual abilities.

Metamorphosis can be induced in axolotls with thyroid hormones including thyroxine and triiodo-L-thyronine. But in its natural adult form, the axolotl is the aquatic, gilled salamander that so many people recognize at once.

If you want to see how much you remember, the quiz is waiting next.