Biology:Axolotl

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Short description: Species of salamander

Axolotl
Ambystoma mexicanum 1zz.jpg
In the National Aquarium in Washington, D.C.
CITES Appendix II (CITES)[2]
Scientific classification edit
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)
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IUCN range of the Axolotl.
  Axolotl (Ambystoma mexicanum)
Synonyms[3]
  • Siredon edule Axolotes guttata
  • Gyrinus mexicanus Shaw and Nodder, 1798
  • Shaw, 1802 Owen, 1844
  • Siredon Humboldtii Siredon axolotl
  • Duméril, Bibron, and Duméril, 1854 Dugès, 1888
  • Siren pisciformis Wagler, 1830
  • Wiedersheim, 1879 Amblystoma weismanni

The axolotl (/ˈæksəlɒtəl/; from Template:Lang-nci [aːˈʃoːloːtɬ] (About this soundlisten)) (Ambystoma mexicanum)[3] is a paedomorphic salamander closely related to the tiger salamander.[3][4][5] It is unusual among amphibians in that it reaches adulthood without undergoing metamorphosis. Instead of taking to the land, adults remain aquatic and gilled. The species was originally found in several lakes underlying what is now Mexico City, such as Lake Xochimilco and Lake Chalco.[1] These lakes were drained by Spanish settlers after the conquest of the Aztec Empire, leading to the destruction of much of the axolotl's natural habitat.

(As of 2020), the axolotl was near extinction[6][7] due to urbanization in Mexico City and consequent water pollution, as well as the introduction of invasive species such as tilapia and perch. It is listed as critically endangered in the wild, with a decreasing population of around 50 to 1,000 adult individuals, by the International Union for Conservation of Nature and Natural Resources (IUCN) and is listed under Appendix II of the Convention on International Trade in Endangered Species (CITES).[2] Axolotls are used extensively in scientific research due to their ability to regenerate limbs, gills and parts of their eyes and brains.[8] Notably, their ability to regenerate declines with age, but it does not disappear. Axolotls keep modestly growing throughout their life and some consider this trait to be a direct contributor to their regenerative abilities.[9] Further research has been conducted to examine their heart as a model of human single ventricle and excessive trabeculation.[10] Axolotls were also sold as food in Mexican markets and were a staple in the Aztec diet.[11]

Axolotls should not be confused with the larval stage of the closely related tiger salamander (A. tigrinum), which are widespread in much of North America and occasionally become paedomorphic. Neither should they be confused with mudpuppies (Necturus spp.), fully aquatic salamanders from a different family that are not closely related to the axolotl but bear a superficial resemblance.[12]

Description

A captive leucistic axolotl, perhaps the most well known form of the axolotl
Face of a common or wild type axolotl
The speckled wild type form
Axolotl's gills (Ambystoma mexicanum)

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 cloacae lined with papillae, while females are noticeable for their wider bodies full of eggs. Three pairs of external gill stalks (rami) originate behind their heads and are used to move oxygenated water. The external gill rami are lined with filaments (fimbriae) to increase surface area for gas exchange.[15] Four-gill slits lined with gill rakers are hidden underneath the external gills, which prevent food from entering and allow particles to filter through.

Axolotls have barely visible vestigial teeth, which develop during metamorphosis. The primary method of feeding is by 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.

Buccal pumping
Axolotls displaying variations in color

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

Lake Xochimilco, Mexico City (Amanecer en Xochimilco). The native habitat of axolotls is important to the study of preservation and conservation.
Wild form

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 Ambystoma tigrinum, species complex, along with all other Mexican species of Ambystoma. Their habitat is like that of most neotenic species—a high-altitude body of water surrounded by a risky terrestrial environment. These conditions are thought to favor neoteny. However, a terrestrial population of Mexican tiger salamanders occupies and breeds in the axolotl's habitat.[citation needed]

Diet

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

Leucistic axolotl in captivity

Today, the axolotl is still used in research as a model organism, and large numbers are bred in captivity. They are especially easy to breed compared to other salamanders in their family, which are rarely captive-bred due to the demands of terrestrial life. One attractive feature for research is the large and easily manipulated embryo, which allows viewing of the full development of a vertebrate. Axolotls are used in heart defect studies due to the presence of a mutant gene that causes heart failure in embryos. Since the embryos survive almost to hatching with no heart function, the defect is very observable. The axolotl is also considered an ideal animal model for the study of neural tube closure due to the similarities between human and axolotl neural plate and tube formation; the axolotl's neural tube, unlike the frog's, is not hidden under a layer of superficial epithelium.[26] There are also mutations affecting other organ systems some of which are not well characterized and others that are.[27] The genetics of the color variants of the axolotl have also been widely studied.[18]

Regeneration

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 base pair long sequence of the axolotl's genome was published in 2018 and was the largest animal genome completed at the time. It revealed species-specific genetic pathways that may be responsible for limb regeneration.[34] Although the axolotl genome is about 10 times as large as the human genome, it encodes a similar number of proteins, namely 23,251[34] (the human genome encodes about 20,000 proteins). The size difference is mostly explained by a large fraction of repetitive sequences, but such repeated elements also contribute to increased median intron sizes (22,759 bp) which are 13, 16 and 25 times that observed in human (1,750 bp), mouse (1,469 bp) and Tibetan frog (906 bp), respectively.[34]

Neoteny

Most amphibians begin their lives as aquatic animals which are unable to live on dry land, often being dubbed as tadpoles. To reach adulthood, they go through a process called metamorphosis, in which they lose their gills and start living on land. However, the axolotl is unusual in that it has a lack of thyroid stimulating hormone, which is needed for the thyroid to produce thyroxine in order for the axolotl to go through metamorphosis; therefore, it keeps its gills and lives in water all its life, even after it becomes an adult and is able to reproduce. Its body has the capacity to go through metamorphosis if given the necessary hormone, but axolotls do not produce it, and must be exposed to it from an external source,[35] after which an axolotl undergoes an artificially-induced metamorphosis and begins living on land. One method of artificial metamorphosis induction is through an injection of iodine, which is used in the production of thyroid hormones.

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.[37] Many other species within the axolotl's genus are also either entirely neotenic or have neotenic populations. Sirens and Necturus are other neotenic salamanders, although unlike axolotls, they cannot be induced to metamorphose by an injection of iodine or thyroxine hormone.

The genes responsible for neoteny in laboratory animals may have been identified; however, they are not linked in wild populations, suggesting artificial selection is the cause of complete neoteny in laboratory and pet axolotls.[38]

Six adult axolotls (including a leucistic specimen) were shipped from Mexico City to the Jardin des Plantes in Paris in 1863. 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.[verification needed] This discovery was the starting point of research about neoteny. It is not certain that Ambystoma velasci specimens were not included in the original shipment.[citation needed] Vilem Laufberger in Prague used thyroid hormone injections to induce an axolotl to grow into a terrestrial adult salamander. The experiment was repeated by Englishman Julian Huxley, who was unaware the experiment had already been done, using ground thyroids.[39] Since then, experiments have been done often with injections of iodine or various thyroid hormones used to induce metamorphosis.[16]

Neoteny has been observed in all salamander families in which it seems to be a survival mechanism, in aquatic environments only of mountain and hill, with little food and, in particular, with little iodine. In this way, salamanders can reproduce and survive in the form of a smaller larval stage, which is aquatic and requires a lower quality and quantity of food compared to the big adult, which is terrestrial. If the salamander larvae ingest a sufficient amount of iodine, directly or indirectly through cannibalism, they quickly begin metamorphosis and transform into bigger terrestrial adults, with higher dietary requirements.[40] In fact, in some high mountain lakes there live dwarf forms of salmonids that are caused by deficiencies in food and, in particular, iodine, which causes cretinism and dwarfism due to hypothyroidism, as it does in humans.

Threats

Axolotls are only native to the Mexican Central Valley. Although the native axolotl population once extended through most of the lakes and wetlands that make up this region, the Native habitat is now limited to Lake Xochimilco as a result of the expansion of Mexico City. Lake Xochimilco is not a large body of water, but rather a small series of artificial channels, small lakes, and temporary wetlands.

Lake Xochimilco is the only native habitat left for the axolotl.

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

These axolotls at Vancouver Aquarium are leucistic, with less pigmentation than normal.
Axolotl in a pet store in Melbourne, Australia

The axolotl is a popular exotic pet like its relative, the tiger salamander (Ambystoma tigrinum). As for all poikilothermic organisms, lower temperatures result in slower metabolism and a very unhealthily reduced appetite. Temperatures at approximately 16 °C (61 °F) to 18 °C (64 °F) are suggested for captive axolotls to ensure sufficient food intake; stress resulting from more than a day's exposure to lower temperatures may quickly lead to disease and death, and temperatures higher than 24 °C (75 °F) may lead to metabolic rate increase, also causing stress and eventually death.[47][48] Chlorine, commonly added to 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]

This animal was X-rayed several times as part of a research project over a period of two years. It was a normal healthy adult (26.3 cm; 159.5 gm) at the beginning of the project and lived several more years after the project ended.[50]

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 Diego Rivera. In 2021, Mexico released a new design for its 50-peso banknote featuring an axolotl along with maize and chinampas on its back.[61][62] It was recognized as "Bank Note of the Year" by the International Bank Note Society.[63] HD 224693, a star in the equatorial constellation of Cetus, was named Axólotl in 2019.[64][65]

The Pokémon Mudkip and its evolutions, added in Pokémon Ruby and Sapphire (2002), take some visual inspiration from axolotls.[60] Additionally, the Pokemon Wooper, added in 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

References

  1. ↑ 1.0 1.1 IUCN SSC Amphibian Specialist Group (2020). "Ambystoma mexicanum". IUCN Red List of Threatened Species 2020: e.T1095A53947343. doi:10.2305/IUCN.UK.2020-3.RLTS.T1095A53947343.en. https://www.iucnredlist.org/species/1095/53947343. Retrieved 12 November 2021. 
  2. ↑ 2.0 2.1 "Appendices | CITES". https://cites.org/eng/app/appendices.php. 
  3. ↑ 3.0 3.1 3.2 Frost, Darrel R. (2018). "Ambystoma mexicanum (Shaw and Nodder, 1798)". American Museum of Natural History. https://research.amnh.org/vz/herpetology/amphibia/Amphibia/Caudata/Ambystomatidae/Ambystoma/Ambystoma-mexicanum. 
  4. ↑ "Mexican Walking Fish, Axolotls Ambystoma mexicanum". https://www.aquariumindustries.com.au/wp-content/uploads/2012/07/Mexican-Walking-Fish.pdf. 
  5. ↑ "Axolotols (Walking Fish)". Aquarium Online. https://www.aquariumonline.com.au/topics/creatures/mexican.htm. 
  6. ↑ Matt Walker (2009-08-26). "Axolotl verges on wild extinction". BBC. https://news.bbc.co.uk/earth/hi/earth_news/newsid_8220000/8220636.stm. 
  7. ↑ PetAquariums.com (22 April 2020). "Are Axolotls Endangered? You Need To Be Careful…" (in en-US). https://www.petaquariums.com/2020/10/21/are-axolotls-endangered-you-need-to-be-careful/. 
  8. ↑ Weird Creatures with Nick Baker (Television series). Dartmoor, England, UK: The Science Channel. 2009-11-11. Event occurs at 00:25.
  9. ↑ Sandoval-Guzmán, Tatiana (August 2023). "The axolotl" (in en). Nature Methods 20 (8): 1117–1119. doi:10.1038/s41592-023-01961-5. ISSN 1548-7091. PMID 37553398. https://www.nature.com/articles/s41592-023-01961-5. 
  10. ↑ Meyer, Sophie; Lauridsen, Henrik; Pedersen, Kathrine; Andersson, Sofie Amalie; van Ooij, Pim; Willems, Tineke; Berger, Rolf M. F.; Ebels, Tjark et al. (2022-11-28). "Opportunities and short-comings of the axolotl salamander heart as a model system of human single ventricle and excessive trabeculation" (in en). Scientific Reports 12 (1): 20491. doi:10.1038/s41598-022-24442-9. ISSN 2045-2322. PMID 36443330. Bibcode: 2022NatSR..1220491M. 
  11. ↑ Tickell, Sofia Castello Y. (30 October 2012). "Mythic Salamander Faces Crucial Test: Survival in the Wild". The New York Times. https://www.nytimes.com/2012/10/31/world/americas/struggle-of-axolotls-mexicos-mythical-salamander.html?pagewanted=all&_r=1. 
  12. ↑ Malacinski, George M. (Spring 1978). "The Mexican Axolotl, Ambystoma mexicanum: Its Biology and Developmental Genetics, and Its Autonomous Cell-Lethal Genes". American Zoologist 18 (2): 195–206. doi:10.1093/icb/18.2.195. 
  13. ↑ San Francisco Examiner (San Francisco, California) 7 August 1887, page 9, authored by Yda Addis
  14. ↑ McIndoe, Rosemary; Smith, D. G. (1984), Seymour, Roger S., ed., "Functional morphology of gills in larval amphibians" (in en), Respiration and metabolism of embryonic vertebrates: Satellite Symposium of the 29th International Congress of Physiological Sciences, Sydney, Australia, 1983, Perspectives in vertebrate science (Dordrecht: Springer Netherlands): pp. 55–69, doi:10.1007/978-94-009-6536-2_4, ISBN 978-94-009-6536-2, https://doi.org/10.1007/978-94-009-6536-2_4, retrieved 2021-05-13 
  15. ↑ 15.0 15.1 15.2 Kardong, Kenneth V (2019) (in English). Vertebrates: comparative anatomy, function, evolution. McGraw-Hill Education. ISBN 978-1-259-70091-0. OCLC 1053847969. https://www.worldcat.org/oclc/1053847969. 
  16. ↑ 16.0 16.1 Safi, Rachid; Bertrand, Stéphanie; Marchand, Oriane; Duffraisse, Marilyne; de Luze, Amaury; Vanacker, Jean-Marc; Maraninchi, Marie; Margotat, Alain et al. (2004-02-01). "The Axolotl (Ambystoma mexicanum), a Neotenic Amphibian, Expresses Functional Thyroid Hormone Receptors". Endocrinology 145 (2): 760–772. doi:10.1210/en.2003-0913. PMID 14576183. 
  17. ↑ "18 Types of Axolotl Colors You Can Own (Axolotl Color Guide)". August 14, 2019. https://exopetguides.com/axolotl/axolotl-colors/. 
  18. ↑ 18.0 18.1 Frost, Sally K.; Briggs, Fran; Malacinski, George M. (1984). "A color atlas of pigment genes in the Mexican axolotl (Ambystoma mexicanum)". Differentiation 26 (1–3): 182–188. doi:10.1111/j.1432-0436.1984.tb01393.x. 
  19. ↑ Pietsch, Paul; Schneider, Carl W. (1985). "Vision and the skin camouflage reactions of Ambystoma larvae: the effects of eye transplants and brain lesions". Brain Research 340 (1): 37–60. doi:10.1016/0006-8993(85)90772-3. PMID 4027646. 
  20. ↑ "Lake Xochimilco, Borough of Xochimilco in southern México City, 162 L • Biotope Aquarium" (in en-GB). https://biotope-aquarium.info/aquariums/lake-xochimilco-borough-of-xochimilco-in-southern-mexico-city-162-l/. 
  21. ↑ Stevenson, M. (2014-01-28). "Mexico's 'water monster' may have disappeared". https://www.sfgate.com/news/science/article/Mexico-s-water-monster-may-have-disappeared-5182823.php. 
  22. ↑ "Endangered 'water monster' Axolotl found in Mexico City lake" (in en-GB). The Independent. 2014-02-24. https://www.independent.co.uk/environment/axolotl-found-in-mexico-city-lake-after-scientists-feared-it-only-survived-in-captivity-9148775.html. 
  23. ↑ "Mexico City's 'water monster' nears extinction". November 2008. https://www.uswaternews.com/archives/arcglobal/8mexicity11.html. 
  24. ↑ 24.0 24.1 "Ambystoma mexicanum (Salamandra ajolote)". https://animaldiversity.org/accounts/Ambystoma_mexicanum/. 
  25. ↑ Wainwright, P. C.; Sanford, C. P.; Reilly, S. M.; Lauder, G. V. (1989). "Evolution of motor patterns: aquatic feeding in salamanders and ray-finned fishes". Brain, Behavior and Evolution 34 (6): 329–341. doi:10.1159/000116519. PMID 2611639. 
  26. ↑ Gordon, R. (1985). "A review of the theories of vertebrate neurulation and their relationship to the mechanics of neural tube birth defects". Journal of Embryology and Experimental Morphology 89 (Supplement): 229–255. PMID 3913733. https://journals.biologists.com/dev/content/89/Supplement/229. 
  27. ↑ Armstrong, John B. (1985). "The axolotl mutants". Developmental Genetics 6 (1): 1–25. doi:10.1002/dvg.1020060102. 
  28. ↑ Caballero-Pérez, Juan; Espinal-Centeno, Annie; Falcon, Francisco; García-Ortega, Luis F.; Curiel-Quesada, Everardo; Cruz-Hernández, Andrés; Bako, Laszlo; Chen, Xuemei et al. (January 2018). "Transcriptional landscapes of Axolotl (Ambystoma mexicanum)" (in en). Developmental Biology 433 (2): 227–239. doi:10.1016/j.ydbio.2017.08.022. PMID 29291975. 
  29. ↑ Roy, S; Gatien, S (November 2008). "Regeneration in axolotls: a model to aim for!". Experimental Gerontology 43 (11): 968–73. doi:10.1016/j.exger.2008.09.003. PMID 18814845. 
  30. ↑ Vieira, Warren A.; Wells, Kaylee M.; McCusker, Catherine D. (2020). "Advancements to the Axolotl Model for Regeneration and Aging". Gerontology 66 (3): 212–222. doi:10.1159/000504294. PMID 31779024. 
  31. ↑ Goodwin, James W.; Pinto, Alexander R.; Rosenthal, Nadia A. (June 4, 2013). Olson, Eric N.. ed. "Macrophages are required for adult salamander limb regeneration". Proceedings of the National Academy of Sciences of the United States of America 110 (23): 9415–9420. doi:10.1073/pnas.1300290110. PMID 23690624. Bibcode: 2013PNAS..110.9415G. 
  32. ↑ Pedersen, Katherine; Rasmussen, Rikke Kongsgaard; Dittrich, Anita; Pedersen, Michael; Lauridsen, Henrik (April 17, 2020). "Modulating the immune response and the pericardial environment with LPS or prednisolone in the axolotl does not change the regenerative capacity of cryoinjured hearts". The FASEB Journal 34 (S1): 1. doi:10.1096/fasebj.2020.34.s1.04015. 
  33. ↑ Masselink, Wouter, and Elly M. Tanaka. "Toward Whole Tissue Imaging of Axolotl Regeneration." Developmental Dynamics, vol. 250, no. 6, 2020, pp. 800–806., https://doi.org/10.1002/dvdy.282.
  34. ↑ 34.0 34.1 34.2 Nowoshilow, Sergej; Schloissnig, Siegfried; Fei, Ji-Feng; Dahl, Andreas; Pang, Andy W. C.; Pippel, Martin; Winkler, Sylke; Hastie, Alex R. et al. (2018-01-24). "The axolotl genome and the evolution of key tissue formation regulators". Nature 554 (7690): 50–55. doi:10.1038/nature25458. ISSN 1476-4687. PMID 29364872. Bibcode: 2018Natur.554...50N. 
  35. ↑ Demircan, Turan; Ovezmyradov, Guvanch; Yıldırım, Berna; Keskin, İlknur; İlhan, Ayşe Elif; Fesçioğlu, Ece Cana; Öztürk, Gürkan; Yıldırım, Süleyman (2018-07-20). "Experimentally induced metamorphosis in highly regenerative axolotl (Ambystoma mexicanum) under constant diet restructures microbiota" (in en). Scientific Reports 8 (1): 10974. doi:10.1038/s41598-018-29373-y. PMID 30030457. Bibcode: 2018NatSR...810974D. 
  36. ↑ 36.0 36.1 "Axolotls - Metamorphosed & Tiger Salamanders". https://www.axolotl.org/tiger_salamander.htm. 
  37. ↑ Ley, Willy (February 1968). "Epitaph for a Lonely Olm". Galaxy Science Fiction: 95–104. https://archive.org/stream/Galaxy_v26n03_1968-02_modified#page/n37/mode/2up. 
  38. ↑ Malacinski, George M. (1978-05-01). "The Mexican Axolotl, Ambystoma mexicanum: Its Biology and Developmental Genetics, and Its Autonomous Cell-lethal Genes". American Zoologist 18 (2): 195–206. doi:10.1093/icb/18.2.195. 
  39. ↑ Reiß, Christian; Olsson, Lennart; Hoßfeld, Uwe (2015). "The history of the oldest self-sustaining laboratory animal: 150 years of axolotl research" (in en). Journal of Experimental Zoology Part B: Molecular and Developmental Evolution 324 (5): 393–404. doi:10.1002/jez.b.22617. ISSN 1552-5015. PMID 25920413. https://onlinelibrary.wiley.com/doi/abs/10.1002/jez.b.22617. 
  40. ↑ Venturi, S. (2004). "Iodine and Evolution. DIMI-Marche". https://sites.google.com/site/iodinestudies/morosini. 
  41. ↑ Nandini, Sarma; García, Pedro Ramirez; Sarma, S. S. S. (2016). "Water quality in Lake Xochimilco, Mexico: zooplankton indicators and Vibrio cholerae" (in en). Journal of Limnology 75 (1). doi:10.4081/jlimnol.2015.1213. ISSN 1723-8633. https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2015.1213. 
  42. ↑ Robles-Mendoza, C.; García-Basilio, C.; Cram-Heydrich, S.; Hernández-Quiroz, M.; Vanegas-Pérez, C. (2009-02-01). "Organophosphorus pesticides effect on early stages of the axolotl Ambystoma mexicanum (Amphibia: Caudata)" (in en). Chemosphere 74 (5): 703–710. doi:10.1016/j.chemosphere.2008.09.087. ISSN 0045-6535. PMID 19012946. Bibcode: 2009Chmsp..74..703R. https://www.sciencedirect.com/science/article/pii/S004565350801223X. 
  43. ↑ Alcaraz, Guillermina; López-Portela, Xarini; Robles-Mendoza, Cecilia (2015-07-01). "Response of a native endangered axolotl, Ambystoma mexicanum (Amphibia), to exotic fish predator" (in en). Hydrobiologia 753 (1): 73–80. doi:10.1007/s10750-015-2194-4. ISSN 1573-5117. https://doi.org/10.1007/s10750-015-2194-4. 
  44. ↑ Parra-Plea, G; Zamudio, K.R.; Recuero, E.; Aguilar-=Miguel, X.; Huaxuz, D.; Zambrano, L. (2011). "Conservation genetics of threatened Mexican axolotls (Ambystoma)". American Conservation 15 (1): 61–72. doi:10.1111/j.1469-1795.2011.00488.x. https://doi.org/10.1111/j.1469-1795.2011.00488.x. 
  45. ↑ Ramos, A.G.; Mena-Gonzalez, H.; Zambrano, L (2021). "The potential of temporary shelters to increase survival of the endangered Mexican axolotl". Aquatic Conservation: Marine and Freshwater Ecosystems 31 (6): 1535–1542. doi:10.1002/aqc.3520. https://doi.org/10.1002/aqc.3520. 
  46. ↑ Paúl, María Luisa (2023-12-01). "Mexico wants you to adopt an axolotl, the amphibian that never grows up" (in en-US). Washington Post. ISSN 0190-8286. https://www.washingtonpost.com/nation/2023/12/01/axolotl-mexican-salamander-adoption-campaign/. 
  47. ↑ "Axolotls – Requirements & Water Conditions in Captivity". https://www.axolotl.org/requirements.htm. 
  48. ↑ "Caudata Culture Species Entry – Ambystoma mexicanum – Axolotl". https://www.caudata.org/cc/species/Ambystoma/A_mexicanum.shtml. 
  49. ↑ Wiegert, Joshua. "Axolotls: Keeping a Water Monster". https://www.tfhmagazine.com/articles/freshwater/axolotls-keeping-a-water-monster-full. 
  50. ↑ Kulbisky, Gordon P; Rickey, Daniel W; Reed, Martin H; Björklund, Natalie; Gordon, Richard (1999). "The axolotl as an animal model for the comparison of 3-D ultrasound with plain film radiography". Ultrasound in Medicine and Biology 25 (6): 969–975. doi:10.1016/s0301-5629(99)00040-x. PMID 10461726. 
  51. ↑ Clare, John P.. "Health and Diseases". https://www.axolotl.org/health.htm. 
  52. ↑ Strecker, Angela L.; Campbell, Philip M.; Olden, Julian D. (2011). "The Aquarium Trade as an Invasion Pathway in the Pacific Northwest". Fisheries 36 (2): 74–85. doi:10.1577/03632415.2011.10389070. https://pdxscholar.library.pdx.edu/esm_fac/40. 
  53. ↑ 53.0 53.1 Pough, F. H. (1992). "Recommendations for the Care of Amphibians and Reptiles in Academic Institutions". Washington, D.C.: National Academy Press. https://netvet.wustl.edu/species/reptiles/pough.txt. 
  54. ↑ Clayton, Leigh Ann; Gore, Stacey R. (2007). "Amphibian Emergency Medicine". Veterinary Clinics of North America: Exotic Animal Practice 10 (2): 587–620. doi:10.1016/j.cvex.2007.02.004. PMID 17577564. 
  55. ↑ Gresens, Jill (2004). "An Introduction to the Mexican Axolotl (Ambystoma mexicanum)". Lab Animal 33 (9): 41–47. doi:10.1038/laban1004-41. PMID 15457201. 
  56. ↑ Wings, O A review of gastrolith function with implications for fossil vertebrates and a revised classification Acta Palaeontologica Polonica 52 (1): 1–16
  57. ↑ Gordon, N, Gastroliths – How I Learned to Stop Worrying and Love Gravel.
  58. ↑ Björklund, N.K. (1993). Small is beautiful: economical axolotl colony maintenance with natural spawnings as if axolotls mattered. In: Handbook on Practical Methods. Ed.: G.M. Malacinski & S.T. Duhon. Bloomington, Department of Biology, Indiana University: 38–47.
  59. ↑ Loh, Richmond (2015-05-15). Common Disease Conditions in Axolotls. https://www.vin.com/apputil/content/defaultadv1.aspx?pId=14365&catId=73681&id=7259254. Retrieved 2022-01-21. 
  60. ↑ 60.0 60.1 60.2 60.3 "Mexico's axolotl, a cartoon hero and genetic marvel, fights for survival" (in en). Reuters. 2018-11-20. https://www.reuters.com/article/us-mexico-axolotl-idUSKCN1NP0F6. 
  61. ↑ "Mexican axolotl will be the new image of the 50 peso bill" (in en-US). 2020-02-21. https://www.theyucatantimes.com/2020/02/mexican-axolotl-will-be-the-new-image-of-the-50-peso-bill/. 
  62. ↑ "Billete de 50 pesos de la familia G" (in es). https://www.banxico.org.mx/billetes-y-monedas/billete-50-pesos-familia-g.html. 
  63. ↑ "Banknote of 2021 Nominations". https://www.theibns.org/joomla/index.php?option=com_content&view=article&id=809:banknote-of-2021-nominations&catid=39:banknote-of-2021&Itemid=51. 
  64. ↑ "Approved names" (in en). https://www.nameexoworlds.iau.org/final-results. 
  65. ↑ "100 000s of People from 112 Countries Select Names for Exoplanet Systems In Celebration of IAU's 100th Anniversary". December 17, 2019. https://www.iau.org/news/pressreleases/detail/iau1912/. 
  66. ↑ Minecraft (October 3, 2020). ""Minecraft Live: Caves & Cliffs - First Look"". https://www.youtube.com/watch?v=DBvZ2Iqmm3M&t=2486s. ""And then we also found out that axolotls are endangered in the real world, and we think it's good to add endangered animals to Minecraft to create awareness about that." - Agnes Larsson" 
  67. ↑ "The Guardian Battle 21180 | Minecraft® | Buy online at the Official LEGO® Shop US" (in en). https://www.lego.com/en-us/product/the-guardian-battle-21180. 
  68. ↑ "Fortnite v13.40 Leaked Skins: Axo, Castaway Jonesy, Crustina & More". 5 August 2020. https://culturedvultures.com/fortnite-v13-40-leaked-skins-axo-castaway-jonesy-crustina/. 
  69. ↑ @FortniteGame. "Axo got a new style just in time for @maisie_williams & @reubenSelby's hand-picked Locker Bundle". https://twitter.com/FortniteGame/status/1425245581480448005.  Missing or empty |date= (help)

External links

Wikidata ☰ Q22718 entry



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