Axolotl

Axolotl
Conservation status
Critically endangered
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Order:	Caudata
Family:	Ambystomatidae
Genus:	Ambystoma
Species:	A. mexicanum
Binomial name
Ambystoma mexicanum (Shaw, 1789)

The Axolotl (Ambystoma mexicanum) is an aquatic salamander native to Mexico. In the Spanish language it is called the ajolote. The name is from the Aztec Nahuatl language, from "atl" meaning water, and "xolotl" meaning dog. It also derives its name from the Aztec God of Death Xolotl, who — according to myth — assumed the amphibian's form in an effort to escape exile, and was killed while in this form.

It is noted for its appearance and its demonstration of neoteny, remaining in its aquatic larval form even as a sexually mature adult, and not undergoing metamorphosis into a terrestrial form.

Description

A fully grown axolotl, at age 18–24 months, ranges in length from 150–450 mm (6–18 inches), although a size close to 230 mm (9 inches) is most common and greater than 300 mm (12 inches) is rare. They have distinctive "fern-like" gill structures that are not covered (as are gills in fish and in frog tadpoles) — usually 3 stalks on each side of the head; the colour of the fern-like part varies although the usual colour is red and it has been known that species with a diet high in red meat gain red gills; axolotls also breathe through the skin and possess lungs. Axolotls have tiny teeth which are hardly noticable and are used to grip food rather then to tear and chew it. They are also known to have a fast regeneration rate where they can regrow limbs and organs.

Axolotls are very closely related to Tiger Salamanders (Ambystoma tigrinum). In colour they range from albino or white (leucistic) to black, through greys, tans and browns. Wild axolotls are rarely white, though all leucistic (white with black eyes) axolotls are descended from a single mutant male brought to Paris in 1863 in a shipment to the Jardin des Plantes in the city. The true albino mutant common in labs and pet stores was created in an American laboratory in the 1950s through hybridization with an albino Tiger Salamander. No axolotls commercially available today are wild caught (since doing so is strictly forbidden), the majority being descended from these same research specimens, even in the pet trade.

Habitat

Only the axolotl is native to Lake Xochimilco and Lake Chalco in central Mexico, however, axolotls have cousins that appear similar to the axolotl and are found through out Mexico as well as many places in the southern United States, often refered to as "mud puppies". Only the axolotl's cousins are found to live in "axalapascos" (volcanic craters filled with water, maare). The water temperature in Xochimilco rarely rises above 20°C (68°F), though it may fall to 6 or 7°C (43°F) in the winter, and perhaps lower.

The wild population has been put under heavy pressure by the growth of Mexico City. Axolotls are also sold as food in Mexican markets, and were a staple in the Aztec diet. It is currently listed by CITES as an endangered species, and by IUCN as critically endangered in the wild with a decreasing population.

Axolotl's neoteny

Axolotls exhibit a property called neoteny, meaning that they reach adulthood without undergoing metamorphosis. Some axolotls metamorphose, although they do so rarely, and usually only after with iodine or shots of thyroxine hormone. Another method for inducing transformation, though one that is very rarely successful, involves removing an axolotl in good condition to a shallow tank in a vivarium and slowly reducing the water level so that the axolotl has difficulty submerging, and eventually is unable submerge at all; it will then stop using its gills to breathe and use its lungs. It will then, over a period of weeks, slowly metamorphose into an adult salamander. During transformation, the air in the vivarium must remain moist, and the maturing axolotl sprayed with a fine mist of pure water. The odds of the animal being able to metamorphose via this method are extremely small, and most attempts at inducing metamorphosis lead to death. Spontaneous metamorphosis has been known to occur very rarely, but attempts to do so artificially are best left to trained scientists. An inability to produce the necessary hormones required for metamorphosis on their own results in such a neotenic existence. Artificial metamorphosis also dramatically shortens the axolotl's lifespan, if they survive the process. A neotenic axolotl will live an average of 10–15 years (though an individual in Paris is credited with achieving 25 years), while a metamorphosed specimen will scarcely live past the age of five. The adult form resembles the adult Tiger Salamander, supporting the theory that the two species are closely related.

Jardin des Plantes story

The first imported axolotls in Europe during the 19th Century were placed in the "Jardin des Plantes" in Paris. Unaware of their neoteny, Auguste Duméril was surprised when, instead of the axolotl, he found in the vivarium a new species, similar to the salamander. This discovery was the starting point of research about neoteny.

Vilem Laufberger's experiment

Vilem Laufberger did a famous experiment in Germany concerning the axolotl. Using hormone injections, he persuaded an axolotl to grow into a fully adult salamander of a species that no one had ever seen. This is because the axolotl is a juvenile form of an amphibian that evolved to be sexually mature still in the 'infant' stage. The experiment was repeated by the Englishman Julian Huxley, who was unaware the experiment had already been done.

Uses in research

The axolotl is used in research and large numbers are bred in captivity. The feature of the salamander that attracts most attention is its healing ability: the axolotl does not heal by scarring and is capable of the regeneration of entire lost appendages in a period of months, and, in certain cases, more vital structures. Some have indeed been found restoring the less vital parts of their brains. They can also readily accept transplants from other individuals, including eyes and parts of the brain — restoring these alien organs to full functionality. In some cases, axolotls have been known to repair a damaged limb as well as regenerating an additional one, ending up with an extra appendage that makes them attractive to pet owners as a novelty. In metamorphosed individuals, however, the ability to regenerate is greatly diminished. Another attractive feature, for research, is the large and robust embryos. Axolotls are especially easy to breed compared to other salamanders in their family, which are almost never captive bred.

Feeding

The axolotl is carnivorous, consuming small prey such as worms, insects, and small fish in the wild.

In captivity, they can be fed a variety of readily available foods, including trout and salmon pellets, frozen or live bloodworms, earthworms, and waxworms on occasion. Beef heart is sometimes recommended, but is not a good choice for the animal as mammal proteins are not readily digestible. Small juveniles can be fed with Daphnia or brine shrimp until old enough for the larger foodstuffs. Axolotls locate food by smell, and will "snap" at any potential meal, sucking the food into their stomachs with vacuum force. This is why other animals may not be housed with axolotls (excluding adults with adults) as anything smaller will invariably end up in their mouths — even siblings. Fish can also nibble an axolotl's gill stalks and appendages while it is asleep, leading to infection.

Elevage conditions

Axolotls live at temperatures of 14–20°C (54–68°F), preferably 17–18°C (62–64°F). Lower temperatures slow down their metabolism, although temperatures around 10 C (50 F) are a panacea when it comes to treating disease. Higher temperatures can lead to stress and increased appetite; use of a cooling aggregate is strongly recommended. Tapwater should be treated with a dechlorinator before the animal is introduced into it, as chlorine is harmful. A single typical axolotl should be kept in a normal 10 U.S. gallon tank (44 litres) with around 150 mm (6 inches) of water. A full tank without a lid can lead to the animal "jumping ship" as it were. A power filter or underwater filter run by an airpump can be used, though water flow should be kept to a minimum to avoid stressing the animal. A 20% water change should be done every week, with debris being siphoned from the bottom. Small gravel should be avoided, as the axolotl can mistakenly ingest the rocks, leading to stress and gas. Floating plants should be provided for juveniles as a hiding place, and small caves should likewise be provided for adults. No light is necessary as axolotls are nocturnal. Axolotls will spend a majority of the time on the bottom of the tank (floating is a sign of stress and illness), so design accordingly.

Cultural references

• Argentinian writer Julio Cortazar wrote a short story named after the salamander.
• The word axolotl is used frequently in crossword puzzles.
• Axolotl tanks are frequently mentioned in Frank Herbert's Dune series of books.
• It was often used in the early years of Mad magazine as a running gag and in-joke, for instance in a parody of Wordsworth's "I Wandered Lonely as a Cloud":

"I wandered lonely as a clod,

Just picking up old rags and bottles,

When onward on my way I plod,

I saw a host of axolotls."

• The axolotl is mentioned in the musical Children of Eden by Stephen Schwartz. In the aptly titled song called "The Naming", Adam and Eve run through a long list of animals that start with the letter "a", at one point going mentioning the axolotl.
• The fictional creatures Wooper and Quagsire from the Pokémon franchise are both based on axolotls.
• The fictional Dr. Shrunk from Animal Crossing: Wild World is an axolotl. If talked to, he will grant you emotions to use ingame.
• In Rene Daumal's book A Night of Serious Drinking there is an extended metaphor relating mankind to axolotls. He states that while an axolotl may be forced into maturity, man cannot be forced but must desire such a transformation.
• Axolotls are also mentioned in Primo Levi's short story, Angelica Farfalla.
• The band Hum titled a song Afternoon With the Axolotls on their 1997 album Downward is Heavenward.
• The webcomic 5ideways has a character that is referred to as "Axolotl"

The band 'Nautilis' have a 2002 electronica album entitled 'Are You an Axolotl' out on the record label 'Planet Mu'

External links

• Care of axolotl as pets
• Axolotl.org
• Short narrated film about the Axolotl