Axolotl: Difference between revisions

Axolotl
In the National Aquarium in Washington, D.C.
Conservation status
Critically Endangered  (IUCN 3.1)[1]
CITES Appendix II (CITES)[2]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Order:	Urodela
Family:	Ambystomatidae
Genus:	Ambystoma
Species:	A. mexicanum
Binomial name
Ambystoma mexicanum (Shaw and Nodder, 1798)
IUCN range of the Axolotl.   Axolotl (Ambystoma mexicanum)
Synonyms[3]
Gyrinus mexicanus Shaw and Nodder, 1798 Siren pisciformis Shaw, 1802 Siredon axolotl Wagler, 1830 Axolotes guttata Owen, 1844 Siredon Humboldtii Duméril, Bibron, and Duméril, 1854 Amblystoma weismanni Wiedersheim, 1879 Siredon edule Dugès, 1888

The axolotl (

As of 2020[update], the axolotl was near

A sexually mature adult axolotl, at age 18–27 months, ranges in length from 15 to 45 cm (6 to 18 in), although a size close to 23 cm (9 in) is most common and greater than 30 cm (12 in) is rare. Axolotls possess features typical of salamander larvae, including external gills and a caudal fin extending from behind the head to the vent.^[13][14] External gills are usually lost when salamander species mature into adulthood, although the axolotl maintains this feature.^[15] This is due to their neoteny evolution, where axolotls are much more aquatic than other salamander species.^[16]

Their heads are wide, and their eyes are lidless. Their limbs are underdeveloped and possess long, thin digits. Males are identified by their swollen

Axolotls have barely visible

suction, during which their rakers interlock to close the gill slits. External gills are used for respiration, although buccal pumping (gulping air from the surface) may also be used to provide oxygen to their lungs.^[15] Buccal pumping can occur in a two-stroke manner that pumps air from the mouth to the lungs, and with four-stroke that reverses this pathway with compression forces.

Axolotls exhibit diverse color variations driven by mutations in their pigmentation genes. These genes play a crucial role in determining the coloration of these unique creatures. Here's a concise list of axolotl color variants:

1. Wild-Type: The standard coloration for axolotls is brown/tan with gold speckles and an olive undertone. This serves as the baseline for comparison with various mutations.
2. Leucistic: Mutations in pigmentation genes result in a leucistic axolotl, characterized by a pale pink hue and distinctive black eyes. This variant is visually striking due to its light coloration.
3. Golden Albino: Axolotls with golden albino mutations exhibit a beautiful golden color with matching gold eyes. This visually appealing variant is highly sought after among axolotl enthusiasts.
4. Xanthic: Xanthic axolotls display a grey color with black eyes, standing out as a unique variation in the spectrum of axolotl pigmentation. The grey hue distinguishes them from the typical wild-type.
5. Albino: Unlike albino mutations in some other species, axolotl albinos are pale pink or white with red eyes. This albino variation is relatively common in axolotls and adds a touch of uniqueness to their appearance.
6. Melanoid: Axolotls with melanoid mutations are characterized by an all-black or dark blue coloration. Unlike the wild-type, melanoid axolotls lack gold speckles and the olive undertone, resulting in a distinct and darker appearance.

^[17] Axolotls come in different colors and patterns. Some have gold speckles that vary in size and intensity. As they grow up, some axolotls develop a black and white piebald look. When people breed them as pets, they often mix different colors, leading to axolotls with both albino and leucistic traits. These are called double homozygous mutants and are common in the pet trade, especially in white/pink axolotls with pink eyes. ^[18] Axolotls can also change their color a bit for better camouflage. They do this by adjusting the size and thickness of their melanophores, which helps them blend in with their surroundings.^[19]

Habitat and ecology

The axolotl is native only to the freshwater of Lake Xochimilco and Lake Chalco in the Valley of Mexico. Lake Chalco no longer exists, having been drained as a flood control measure, and Lake Xochimilco remains a remnant of its former self, existing mainly as canals. The water temperature in Xochimilco rarely rises above 20 °C (68 °F), although it may fall to 6–7 °C (43–45 °F) in the winter, and perhaps lower.^[20]

Surveys in 1998, 2003, and 2008 found 6,000, 1,000, and 100 axolotls per square kilometer in its Lake Xochimilco habitat, respectively.^[21] A four-month-long search in 2013, however, turned up no surviving individuals in the wild. Just a month later, two wild ones were spotted in a network of canals leading from Xochimilco.^[22]

The wild population has been put under heavy pressure by the growth of Mexico City. The axolotl is currently on the International Union for Conservation of Nature's annual Red List of threatened species. Non-native fish, such as African tilapia and Asian carp, have also recently been introduced to the waters. These new fish have been eating the axolotls' young, as well as their primary source of food.^[23]

Axolotls are members of the tiger salamander, or

The axolotl is carnivorous, consuming small prey such as mollusks,[24] worms, insects, other arthropods,^[24] and small fish in the wild. Axolotls locate food by smell, and will "snap" at any potential meal, sucking the food into their stomachs with vacuum force.^[25]

Use as a model organism

Today, the axolotl is still used in research as a

The feature of the axolotl 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, such as tail, limb, central nervous system, and tissues of the eye and heart.^[28] They can even restore 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. The axolotl is therefore used as a model for the development of limbs in vertebrates.^[29] There are three basic requirements for regeneration of the limb: the wound epithelium, nerve signaling, and the presence of cells from the different limb axes.^[30] A wound epidermis is quickly formed by the cells to cover up the site of the wound. In the following days, the cells of the wound epidermis divide and grow quickly forming a blastema, which means the wound is ready to heal and undergo patterning to form the new limb.

It is believed that during limb generation, axolotls have a different system to regulate their internal macrophage level and suppress inflammation, as scarring prevents proper healing and regeneration.^[31] However, this belief has been questioned by other studies.^[32] The axolotl's regenerative properties leave the species as the perfect model to study the process of stem cells and its own neoteny feature. Current research can record specific examples of these regenerative properties through tracking cell fates and behaviors, lineage tracing skin triploid cell grafts, pigmentation imaging, electroporation, tissue clearing and lineage tracing from dye labeling. The newer technologies of germline modification and transgenesis are better suited for live imaging the regenerative processes that occur for axolotls.^[33]

Genome

The 32 billion

Most amphibians begin their lives as

An axolotl undergoing metamorphosis experiences a number of physiological changes that help them adapt to life on land. These include increased muscle tone in limbs, the absorption of gills and fins into the body, the development of eyelids, and a reduction in the skin's permeability to water, allowing the axolotl to stay more easily hydrated when on land. The lungs of an axolotl, though present alongside gills after reaching non-metamorphosed adulthood, develop further during metamorphosis.[36]

An axolotl that has gone through metamorphosis resembles an adult plateau tiger salamander, though the axolotl differs in its longer toes.^{[citation needed]} The process of artificially inducing metamorphosis can often result in death during or even following a successful attempt, and so casual hobbyists are generally discouraged from attempting to induce metamorphosis in pet axolotls.^[36]

Neoteny is the term for reaching sexual maturity without undergoing metamorphosis.

Lake Xochimilco has poor water quality, caused by the region's aquaculture and agriculture demands. It is also maintained by inputs of only partially treated wastewater. Water quality tests reveal a low nitrogen-phosphorus ratio and a high concentration of chlorophyll a, which are indicative of an oxygen-poor environment that is not well-suited for axolotls.^[41] In addition, the intensive use of pesticides from agriculture around Lake Xochimilco causes run off into the lake and a reduction of habitat quality for axolotls. The pesticides used contain chemical compounds that studies show to sharply increase mortality in axolotl embryos and larvae. Of the surviving embryo and larvae, there is also an increase of morphological, behavior, and activity abnormalities.^[42]

Another factor that threatens the native axolotl population is the introduction of invasive species such as the Nile tilapia and common carp. These invasive fish species threaten axolotl populations by eating their eggs or young and by out-competing them for natural resources. The presence of these species has also been shown to change the behavior of axolotls, causing them to be less active to avoid predation. This reduction in activity greatly impacts the axolotls foraging and mating opportunities.^[43]

With such a small native population, there is a large loss of genetic diversity. This lack of genetic diversity can be dangerous for the remaining population, causing an increase in inbreeding and a decrease in general fitness and adaptive potential. It ultimately raises the axolotl's risk for extinction, something that they are already in danger of. Studies have found indicators of a low interpopulation gene flow and higher rates of genetic drift. These are likely the result of multiple “bottleneck” incidents in which events that kill off several individuals of a population occur and sharply reduce the genetic diversity of the remaining population. The offspring produced after bottleneck events have a greater risk of showing decreased fitness and are often less capable of adaptation down the line. Multiple bottleneck events can have disastrous effects on a population. Studies have also found high rates of relatedness that are indicative of inbreeding. Inbreeding can be especially harmful as it can cause an increase in the presence of deleterious, or harmful, genes within a population.^[44]

There has been little improvement in the conditions of the lake or the population of native axolotls. Many scientists are focusing their conservation efforts on translocation of captive-bred individuals into new habitats or reintroduction into Lake Xochimilco. The Laboratorio de Restauracion Ecologica (LRE) in the Universidad Nacional Autonoma de Mexico (UNAM) has built up a population of more than 100 captive-bred individuals. These axolotls are mostly used for research by the lab but plans of a semi-artificial wetland inside the university have been established and the goal is to establish a viable population of axolotls within it. Studies have shown that captive-bred axolotls that are raised in a semi-natural environment can catch prey, survive in the wild, and have moderate success in escaping predators. These captive-bred individuals can be introduced into unpolluted bodies of water or back into Lake Xochimilco to establish or re-establish a wild population.^[45][46]

Captive care

tapwater, is harmful to axolotls. A single axolotl typically requires a 150-litre (40-US-gallon) tank. Axolotls spend the majority of the time at the bottom of the tank.^[49]

Salts, such as Holtfreter's solution, are often added to the water to prevent infection.^[51]

In captivity, axolotls eat a variety of readily available foods, including trout and salmon pellets, frozen or live

bloodworms, earthworms, and waxworms. Axolotls can also eat feeder fish, but care should be taken as fish may contain parasites.^[52]

Substrates are another important consideration for captive axolotls, as axolotls (like other amphibians and reptiles) tend to ingest bedding material together with food[53] and are commonly prone to gastrointestinal obstruction and foreign body ingestion.^[54] Some common substrates used for animal enclosures can be harmful for amphibians and reptiles. Gravel (common in aquarium use) should not be used, and is recommended that any sand consists of smooth particles with a grain size of under 1mm.^[53] One guide to axolotl care for laboratories notes that bowel obstructions are a common cause of death, and recommends that no items with a diameter below 3 cm (or approximately the size of the animal's head) should be available to the animal.^[55]

There is some evidence that axolotls might seek out appropriately-sized gravel for use as

gastroliths^[56] based on experiments conducted at the University of Manitoba axolotl colony,^[57][58] but these studies are outdated and not conclusive. As there is no conclusive evidence pointing to gastrolith use, gravel should be avoided due to the high risk of impaction.^[59]

Cultural significance

The species is named after the

Aztec deity Xolotl, the god of fire and lightning, who transformed himself into an axolotl to avoid being sacrificed by fellow gods. They continue to play an outsized cultural role in Mexico.^[60] Axólotl also means water monster in the Nahuatl

language.

They appear in the works of Mexican muralist

International Bank Note Society.^[63] HD 224693, a star in the equatorial constellation of Cetus, was named Axólotl in 2019.^[64][65]

The

Pokémon Gold, Silver and Crystal (1999), is directly based on an axolotl.^{[60][additional citation(s) needed]} The looks of the dragons Toothless and The Night Fury in the How to Train Your Dragon movies are based on axolotls.^[60] They were also added to the video game Minecraft in 2020. It is following Mojang Studios' trend of adding endangered species to the game to raise awareness.^[66] They were also added to its spin-off Minecraft: Dungeons in 2022 and are available in Lego Minecraft.^[67] An anthropomorphic Axolotl named Axo was also added as a purchasable outfit in Fortnite Battle Royale on August 9, 2020.^[68][69]

See also

• Mudpuppies
• Olm
• Texas salamander
• Texas blind salamander
• Lake Patzcuaro salamander
• Barred tiger salamander
• Amphibious fish
• Handfish
• Regenerative biomedicine

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External links

Wikimedia Commons has media related to Ambystoma mexicanum.

• Ambystomatidae at
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• Follow the Eggs, Hatchlings and Juveniles
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• Indiana U Axolotl Colony
• University of KY Axolotl Colony
• Mystical amphibian venerated by Aztecs nears extinction
• The animal that’s everywhere and nowhere
• "Axolotl" . Encyclopædia Britannica. Vol. 20 (11th ed.). 1911. p. 63.