Tenochtitlan on Lake Texcoco
Modern Mexico City: a super metropolis of nine million people, was once a series of lakes. The Aztec capital, Tenochtitlan, was located there on a network of artificial islands. In those lakes, in countless numbers, swam the axolotl, Ambystoma mexicanum, a wholly aquatic salamander. According to Aztec mythology, the underworld god Xolotl transformed himself into an axolotl to escape being murdered. In a world composed of diverse, and at times weird, animals axolotls stand out as being very strange. The axolotl has a link to the underworld and a legend of divinity.
Axolotls are neotenic. Set apart from most amphibians, the axolotl never transforms into a terrestrial organism. It maintains gills (clearly visible as six long tree-like appendages at the back of their head) and a tail for swimming throughout their entire lifespan. They resemble a tadpole that is in the middle of it’s transformation into a frog, when it has grown arms and legs but has not “lost” its tail yet. Although it seems as though the axolotl should be stunted by its inability to achieve metamorphosis, the fact is that the axolotl achieves far more growth and life expectancy compared to the tiger salamander (a non-neotenic salamander of which the axolotl is genetically close to). Adult axolotls range from nine to twelve inches in length and can live for up to twenty five years; although a lifespan of ten to fifteen years is typical. They are freshwater carnivores hunting worms, minnows, and aquatic insects via smell.
Xolotl was the god of misfortune, and bad luck is currently dogging the wild axolotl. The lakes of the Mexican basin have been one of the most populated areas of the western hemisphere since the fourteenth century. Axolotl tacos were a favorite meal of the inhabitants for centuries and the creature was overfished up until the twentieth century…when the lakes were drained to prevent flooding. Now the lakes largely exist in huge pipes deep below the city and as a series of polluted channels and small reservoirs. Not only are these remaining canals choked with pollution, but super competitive non-native fish have been introduced, most prominently the African tilapia and the Asian carp.
Axolotls are nearly extinct in the wild, and it is uncertain whether they will survive there much longer. The animals have, however found a dark refuge which ensures their continuing existence. As a result of their neoteny, axolotls have extraordinary abilities to heal themselves. Not only can they completely regrow lost arms and legs back to full size and function, they can also regenerate damaged vital organs – including portions of their brains. Axolotls do not heal by scarring, but seem to use some more fundamental ability to regenerate. Of course these remarkable abilities can not help axolotls when they are cooked into a burrito or devoured whole by a carp, but their unusual healing has brought them to the attention of biologists and medical scientists (as has their longevity in comparison with similar salamanders).
Axolotls have joined fruit flies, mice, zebrafish, and rhesus monkeys as a model animal for the laboratory. The salamanders may individually be vivisected, dissected, and subjected to crazy organ transplants or chemical manipulations, but overall they have found an ecosystem to thrive in. Their population numbers have been growing and axolotls will not be extinct until life science is. Indeed if the field of regenerative medicine begins to flourish, all of humankind might have reason to revere the axolotl far more than the Aztecs esteemed Xolotl.