History & Classification of the Axolotl
Mexican Axolotl
(Ambystoma mexicanum)
Above: Nammu, October 2016, 11 months old, female GFP Leucistic Axolotl (A. mexicanum)
Taxonomy
To really appreciate the unique nature and origins of A. mexicanum one should have a working knowledge of what it is and where it comes from. Often mistaken for lizards or odd fish, the Axolotl is an Neotenic Salamander (never leaves it's larval stage or aquatic home) and is characteristic of the genus in many ways. There are also many attributes that set it apart into a distinct species all it's own, recognizeable across the globe. Let's begin by going over A. mexicanum's classification.
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Common Names: Axolotl, Mexican Axolotl, Mexican Salamander, Mexican Walking Fish, Water Dog
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Urodela
Family: Ambystomatidae
Genus: Ambystoma (Mole Salamanders)
Species: A. mexicanum
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Axolotl are often seen in museum aquariums because they are believed to be largely unchanged examples of their ancient ancestors from millions of years ago.
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The order Urodela differentiated approximately 360 million years ago, and the first known salamander fossils were Kokartus honorarius (Middle Jurrasic, Kyrgyzstan) and 2 species of neotenic/aquatic Mamorerpetan salamanders (Middle Jurassic, England). Karaurus sharovi was similar to the modern mole salamander in biology and came later (Upper Jurassic, Kazakhstan) and by the Upper Crustaceous period most salamander families had arrived on the scene. A. mexicanum is estimated to have come into it's own approximately 140 million years ago.
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Relatives
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Closely related to The Tiger Salamander (A. tigrinum), the Axolotl can interbreed with this species. No specimens have been found in the wild as such but the crossbreeding has been performed successfully in a lab setting. Tiger Salamanders do occasionally have individuals who remain neotenic and become sexually mature in their aquatic larval stage. The larval stage of the Tiger Salamander is often confused by new hobbyists as an Axolotl, only to be discovered upon metamorphosis into an adult A.tigrinum.
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Other salamanders in the "Mole Salamander" genus have larval stages similar to the Axolotl such as;
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Spotted Salamanders (A. maculatum)
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Marbled Salamanders (A. opacum)
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There are also species of aquatic salamander that live in lakes and rivers across much of North America that people talk about when meeting my Axolotl for the first time. Some of these are;
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Mudpuppy (Necturus maculosus)
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Hellbender (Cryptobranchus alleganiensis)
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The Olm (Proteus anguineus)
Origins
Left: Jade, GFP Wildtype, 11 months old, female Axolotl.
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Wildtype is the original colour of the Axolotl. Ranging from soft olive green with brown spots/splotches to almost black with black markings they are one of the most striking colour patterns with a great amount of variance from one individual to the next.
The Axolotl originates from the area we now call Mexico City, Mexico. Specifically it made it's home in only 2 lakes; Lake Xochimilco and Lake Chalco. Tragically Lake Chalco no longer exists- it was drained to prevent flooding and Lake Xochimilco is a shadow of it's former self, now merely a series of canals in the market district of Mexico City. A slow decline, the drainage of the Lakes began in the 17th century when Mexico City had expanded with Lake Chalco being drained completely in the past decade.
These lakes are at an elevation of 2,290m above sea level and their temperature rarely rises above 20°C (68°F), though they may fall to 6 or 7°C (43°F) in the winter. Although Mexico is often hot, this area is at a high elevation and Lake Xochimilco is glacially fed from the mountains nearby. It is worth mentioning that these water bodies are low in Iodine which is an important chemical component in a salamander's metamorphosis, possibly contributing to the Axolotl's status as an inducible obligate neotene. Read more about the process of metamorphosis on the "Biology" page
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Axolotl have been a traditional part of the culture of the area for hundreds of years. Once considered a delicacy, it is still sold in the local food markets. The fat of the animal has been used for medicine, and the Axolotl is mentioned in Mayan myths and stories.
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The name Axolotl comes from the Aztec language Nahuatl, "Atl" & "Xolotl" roughly translated to "Water Dog". There is also some reference to the Axolotl in the story of Xolotl and his twin brother Quetzacoatl. Xolotl was an aztec god believed to be the patron of the dead and resurrected (in these instances he took the form of a dog), games, grotesque beings or mutants and twins.
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Lore says he transformed himself into various animals to escape banishment, including an Axolotl. Despite his efforts he was captured and subsequently killed, then fed to the sun and moon.
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History in Captivity
Named by G.Shaw in 1789 the Axolotl was a surprise to everyone. Jardin des Plantes in Paris, France received the first shipment of 6 Axolotl in 1863, one of them being the first Leucistic individual, a male. These animals originated from Lake Xochimilco as did the 33 individuals sent to Paris again in 1864, and the Axolotl sent in 1868. These specimens would be the beginning of the lines of Axolotl that we now see in laboratories around the world. Metamorphosis in captivity was first induced by Vilem Laufberger of Germany, then Julian Huxley- both using thyroid hormones. I have read that there is speculation that tiger salamanders have been integrated into the early lines but could not find many details (If you've got them, e-mail me!)
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Used heavily in medical research due to their miraculous regenerative abilities (read details on the "Biology" page), and sought after in the pet trade, the Axolotl has survived on in captivity. Pet owner's are attracted to it's adorable facial expression and odd mannerisms, and it's relatively easy maintenance requirements combined with a long life span. Thanks to breeders the Axolotl now comes in a stunning spectrum of colours and markings (Also covered in the "Biology" section) with more being developed as we speak.
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Institutions like Mexico's National Autonomous University, Ottawa University, the University of Manitoba and the University of Indiana have all had or still have breeding colonies of Axolotl for research and conservation purposes. The Axolotl is often a frequent occupant of museums and zoos for the same reason it appeals as a pet and for it's historical value.
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The Mexican Axolotl has been restricted in international trade since 1975, and all animals currently for sale are captive bred.
Population & Conservation
Above: Jade, GFP Wildtype Axolotl in the 55 gallon tank she shares with "My Other Axolotls".
A. mexicanum is considered a Critically Endangered in the Wild species by the IUCN (International Union for Conservation of Nature), and is listed by CITES (Convention on International Trade in Endangered Species) as an endangered species.
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Catastrophic loss of habit, heavy pollution, proximity to an urban area and all that implies, local fishing and predation from invasive species like African Tilapia and Asian Carp has resulted in no individuals being found in the wild in the most recently documented 4 month survey performed by Mexico's National Autonomous University in 2013. They did have two sightings reported in THIS article from independant.co.uk in February 2014.
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While conservation efforts are being made in Mexico City via nature tourism, bioremediation and awareness is being raised around the world, the future of A. mexicanum in the wild looks dire. Durrell Institute of Conservation and Ecology is heading a Darwin project to help Mexico come up with a program that focuses on more sustainable development and conservation of Lake Xochimilco Flora and Fauna, Axolotl included.
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The Axolotl's appeal as a research animal and pet for the hobbyists have saved it from total extinction but the next few years will make the difference between extinction in the wild, or a comeback in the canals that are the only remnants of Lake Xochimilco.
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Find out more about how you can fundraise, donate or participate in a monthly program to champion endangered animals (including the Axolotl) at "EDGE (Evolutionary Distinct & Globally Endangered)".
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