By Julie Etra

The first time I saw the salamander called axolotl(s) (Ambystoma mexicanum, aka ajolote) endemics of the remnant lakes of the Valley of Mexico and now confined to Xochimilco, was in Xochimilco at one of the tourist ‘museums’ along a main canal.

The pinkish creatures on exhibit are commercially produced, and not native to the polluted waters of Xochimilco, the wetland system in the heart of Mexico City. and they exhibit the pinkish color of domestication. Wild populations are brown/tan with gold speckles and an olive undertone. This critically endangered species lost most of its habitat centuries ago due to the draining of the valley by the conquering Spaniards, with Xochimilco now a vestige of its former self. Axolotls have a lizard-like head, described as “friendly-faced,” surrounded by feathery gills, four legs, and a tail. They range in size from 6 to 18 inches.

Cute, But Critically Endangered

The axolotl is only found in the wild in the waters of Xochimilco. A 2003 study by the Mexican Academy of Sciences found an average of 6,000 axolotls for each sq km of Xochimilco, about 1,020,000 axolotls; by 2015, it was down to 36 per sq km, or about 6,120. A more recent study found fewer than a thousand in all of the 170 square kilometers of Xochimilco.

The ancient Aztec capital of Tenochtitlán, now Mexico City, was founded in the early 1300s CE on an island in Lake Texcoco. Texcoco was connected with four other lakes in the Valley of Mexico, one of which was Xochimilco. After the Spaniards conquered the Aztecs in 1521, they drained much of the valley, leaving Xochimilco a vestige of its former self.

Habitat for the axolotl was sharply reduced but still existed up until about the 1950s. Since then, habitat degradation has accelerated as rapid urbanization has changed the distribution, movement, and management of water systems in the Valley.

In addition, the water system has been degraded by pollution from urban runoff and uncontrolled development, raw sewage, agricultural waste, and land use conversion, and has been reduced by drawdown of lake levels to supply water to Mexico City and the surrounding environs. Today, most of the water in Xochimilco’s canals comes from a water treatment plant in nearby Cerro de la Estrella, but supplies are inconsistent.

Predation is also a factor in the axolotl’s decline. Carp and tilapia were introduced in Xochimilco in the 1970s in an effort to increase food supplies; unfortunately, they prey on axolotl eggs and young. Loss of shade cover and food – they eat mollusks, worms, insect larvae, brine shrimp, other small crustacea, and small fish – also continue to accompany loss of habitat.

Why is it so important to “bring back” the wild axolotl? For the same reason preserving all species is important – genetic variation. As noted below, the axolotl is very important to biological research, as it is one of the few animals that can regenerate lost body parts. Commercial breeding technology reduces genetic variation, thus weakening the organism’s ability to adapt. This affects the animal’s ability to survive in the wild, and to respond to changes introduced in research.

Physiology and Morphology

This rather large salamander has a number of physiological features that make it unusual. Although it is one species of tiger salamander, it is unique in its “neoteny,” a zoological term that means the retention of juvenile features into adulthood, that is, the axolotl never undergoes metamorphosis, for example, the process of a tadpole changing to a frog. The axolotl’s gills remain external, and they retain their tail fins. Unlike other salamanders this one never makes it to land, completing its life cycle entirely in the water.

The axolotl is important for research because it has can rapidly regenerate parts of itself, making it useful for studying the potential for tissue regeneration in humans. In just a few months, they can regenerate not just their tails, but their skin, muscles, bones, blood vessels, central nervous system, heart, and brain.

What other animals can regenerate body parts? In fact, quite a few. Other species of salamanders can regenerate their tails; starfish can regenerate their “arms” and their bodies from arms; sharks regrow their teeth throughout their lives. The Mexican tetra, a fresh water fish, can regrow heart tissue. Many lizards, including iguanas, skinks, anoles, and geckos, can regenerate their tails. But none of these can do as much as the axolotl.

Despite remaining juvenile all their lives, axolotls reach sexual maturity at 17-27 months and can breed several times a year. Because their habitat is entirely aquatic – that is, no drought conditions – they can generate more offspring per breeding event (salamanders do not reproduce well, often not at all, under drought conditions). After the courtship dance, the female axolotl takes up the sperm capsule deposited by the male. Fertilized eggs are laid individually on aquatic vegetation.

The Axolotl in Mythology

The axolotl loomed large in Mexica (the Aztec group that built Tenochtitlán) mythology, and they were included in their art and creation myths. The name axolotl (from the Nahuatl atl = “water” and xólotl = “monster” or “dog”) means water monster or water dog, and is the aquatic form of Xólotl, the Aztec god of fire and lightning and the twin brother of Quetzalcóatl (the feathered serpent deity).

According to Aztec legend – and there are many versions of each legend – when the sun was created, it did not move. Each god was supposed to sacrifice a body part to make the sun move and to begin life, but Xólotl did not want to sacrifice any part of himself. To hide from fellow gods (would-be assassins), Xólotl transformed himself into a variety of plants and animals, including the xoloitzcuintle, the hairless pre-Columbian dog. The axolotl was his last camouflage before he was captured and killed.

The Axolotl in Literature

An obscure short story, written in 1954, was brought to my attention by a good and extremely literate friend from Pluma Hidalgo. “Axolotl” is by the French-Argentinian writer Julio Cortázar (1914-84), and was published in his 1956 collection End of the Game and Other Stories. The story is told by a lonely man visiting the aquarium at the zoo (ménagerie) at the Museum of Natural History in Paris. He becomes fascinated and obsessed by the axolotls and eventually believes he has been transformed into one of them. Although I read it in English, I found it to be dark and depressing, and overly descriptive. (Available through the University of Kentucky at http://www.ambystoma.uky.edu/teachers_materials/axolitbook/AxolotlByJulioCortazar.html.)

Another read is Axolotiada: Vida y mito de un anfibio mexicano (Axolotiada: Life and Myth of a Mexican Amphibian), by Mexican anthropologist Roger Bartra Murià (2011). An anthology of works about the famous amphibian, the book includes texts from the Mesoamerican codices to the work of authors such as Cortázar, Satoshi Tajir, Aldous Huxley (“A Fetal Monkey”), Primo Levi (“Angelical Butterfly”) and Octavio Paz (“Salamandra”), among others, along with graphics from street graffiti to the scientific illustrations of landscape painter José María Velasco and the murals of Diego Rivera.

Axolotls for the Laboratory

The majority of commercially-bred axolotls in the world today trace their ancestry to a shipment of 34 axolotls from Xochimilco to Paris in 1863, delivered to the zoo at the Museum of Natural History, the very place that inspired Cortázar to write his strange tale. The amphibian is easy to breed in captivity and prolific. Animals were then supplied to various labs throughout Europe for research purposes.

Axolotls came from Europe to the US in 1935; five of those eventually made it into the hands of Dr. Rufus R. Humphrey, who bred more at the University of Buffalo. When he retired in 1957, Humphrey and his axolotls moved to Indiana University (the axolotls arrived in Bloomington by truck). When the head of the Indiana lab retired in 2005, the US axolotl collection relocated to the University of Kentucky and became the Ambystoma Genetic Stock Center (AGSC), but the genetic material has apparently bottlenecked from inbreeding. Thus the importance of saving the wild axolotl population in Xochimilco.

The Icon

The salamander has become so popular that in addition to being kept as pets, it recently won a 2017 contest to develop an “emoji pack” to represent Mexico City. There’s a Frida Kahlo axolotl, a Mexican flag axolotl wrapped in a snake, etc., etc.

If you look online in Mercado Libre or Amazon Mexico, or pretty much anywhere, you’ll find multiple axolotl accessories, particularly for children – charms, stuffed animals (peluche), coloring books. There are tee shirts for adults, not to mention beer (www.monstruodeagua.mx/)! In 2022, the Bank of Mexico issued a new 50-peso bill with a depiction of the now iconic salamander among the chinampas of Xochimilco on one side. On February 1, 2023 (National Axolotl Day in Mexico, in case you were wondering), the Chapultepec Zoo opened Anfibion, the Axolotl Museum and Amphibian Conservation Center, dedicated to the amphibian’s remarkable history and efforts to preserve the species.

Axolotls as Food

The Mexica fished and consumed axolotls – they were a supposed mainstay on the banquet tables of Aztec kings. And how did the Mexica prepare them? Pretty simple. First, the “hairs” (presumably the gills) were trimmed. Then the guts were removed, the remaining carcass washed and dried, seasoned with salt and dried chiles, wrapped in corn husks, and finally steamed. Provecho!

Some Xochimilco natives grew up eating axolotls in a type of tamale, combined with fish and vegetables.

I find this particularly interesting since the skin, in particular, of most salamanders, including other tiger salamanders, is toxic. Contact can numb some parts of the body, starting from the lips, tongue, the whole face, then going down to the arms and legs. Numbness can be followed by dizziness, muscle weakness, excessive drooling (no kidding), and finally to paralysis of the respiratory muscles. Axolotls, however, lack the skin glands that secrete the toxic mucus that protects against predators and poisons those who eat the skin.

Saving the Axolotl

Recently, serious efforts have focused on an ecosystem approach, restoring habitat at a very small scale. To support a native, successfully breeding population requires that you restore water quality and reduce, if not eliminate, any introduced predators. The revival of the ancient, traditional system of chinampa farming in the floating gardens of Xochimilco is the key to preserving the axolotls. For more on the chinampas, see my article “Chinampas, Calzadas, and Aqueducts,” in the February 2023 issue of The Eye (https://theeyehuatulco.com/?s=chinampas).

Political will, accompanied by active participation by the chinamperos, is obviously essential as symbiotic restoration of traditional farming provides the needed habitat.

In late 2023, The New York Times ran an article, “What It Takes To Save the Axolotl,” describing the comprehensive, albeit painstakingly slow and incremental, approach being implemented by the government and a team of biologists and farmers. High-quality sanctuaries are being recreated in isolated waters to support axolotl growth and reproduction while limiting predatory attacks by exotic fish (https://www.nytimes.com/2023/12/05/science/mexico-axolotl-biology.html).

In the early 2000s, the Mexican government had approached Dr. Luis Zambrano, an ecologist at the National Autonomous University of Mexico (UNAM), to survey the declining population. His UNAM lab is home to 150 axolotls from wild bloodlines. In 2017 he released 10 animals into an artificial lake on the campus to observe their behavior and collect data. This research continues. In addition to Dr. Zambrano, another team headed by biologist María Huitzil is studying the animal’s microbiota e.g., bacteria, fungi, viruses etc.; an additional group of researchers is being led by Dr. José Antonio Ocampo.

Dr. Zambrano recently released 12 animals in bamboo cages lowered into excavated soils in the artificial lake. The keys to creating successful isolated refuges are surprisingly simple and elegant: semipermeable volcanic rocks filter the water and block predators (the rock is readily available given the volcanic activity in the area), and vegetation provides habitat. Revived techniques of organic farming are becoming more accepted by some chinamperos, thus reducing contamination. Carlos Sumano, a UNAM agronomist, has for the past 11 years personally promoted traditional farming methods on his own chinampas.

And what happened to the 12 axolotls Zambrano released? After two months one of the 12 had died “of causes yet to be determined, and a pump had to be installed to improve oxygen levels in one canal. ‘But that’s all part of the experiment, right?’ Dr. Zambrano said. The rest of the axolotls were fat and happy.”

For more reading:

“A Tale of Two Axolotls” (www.academic.oup.com/bioscience/article/65/12/1134/223981)
“Axolotls in Crisis: The fight to Save the ‘Water Monster’ of Mexico City”
(www.theguardian.com/cities/2018/dec/04/axolotls-in-crisis-the-fight-to-save-the-water-monster-of-mexico-city)