{{Short description|Species of salamander}}{{Other uses}}{{pp-move}}{{pp-pc|small=yes}}{{Speciesbox| name = Axolotl| image = Ambystoma mexicanum 1zz.jpg

National Aquarium (Washington, D.C.)>National Aquarium in Washington, D.C.| status = CR| status_system = IUCN3.1

TITLE=AMBYSTOMA MEXICANUM

PAGE=E.T1095A53947343

ACCESS-DATE=12 NOVEMBER 2021, | status2 = CITES_A2| status2_system = CITES

access-date=2022-01-14|website=cites.org}}| genus = Ambystoma| species = mexicanum

George Shaw (biologist)>Shaw and Nodder, 1798)| synonyms = {hide}species list

| Gyrinus mexicanus | Shaw and Nodder, 1798
| Siren pisciformis | Shaw, 1802
| Siredon axolotl | Wagler, 1830
| Axolotes guttata | Owen, 1844
| Siredon Humboldtii | DumÃ©ril, Bibron, and DumÃ©ril, 1854
| Amblystoma weismanni | Wiedersheim, 1879
| Siredon edule | DugÃ¨s, 1888 {edih}| synonyms_ref =

frame=yes

from=Ambystoma mexicanum range.map}}| range_map_caption = IUCN range of the Axolotl.{{leftlegend|#FF0000|Axolotl (Ambystoma mexicanum)}}}}The axolotl ({{IPAc-en|Ëˆ|Ã¦|k|s|É™|l|É’|t|É™l|audio=en-us-axolotl.oga}}; from {{IPA-nah|aËËˆÊƒoËloËtÉ¬||Axolotl.ogg}}) (Ambystoma mexicanum) is a paedomorphic salamander closely related to the tiger salamander.WEB,www.aquariumindustries.com.au/wp-content/uploads/2012/07/Mexican-Walking-Fish.pdf, dead,web.archive.org/web/20180315144303/https://www.aquariumindustries.com.au/wp-content/uploads/2017/07/Mexican-Walking-Fish.pdf, 15 March 2018, Mexican Walking Fish, Axolotls Ambystoma mexicanum, WEB,www.aquariumonline.com.au/topics/creatures/mexican.htm, 10 April 2013, dead,www.aquariumonline.com.au/topics/creatures/mexican.htm," title="web.archive.org/web/20130410234310www.aquariumonline.com.au/topics/creatures/mexican.htm,">web.archive.org/web/20130410234310www.aquariumonline.com.au/topics/creatures/mexican.htm, Axolotols (Walking Fish), Aquarium Online, 2013-09-12, 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. 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 extinctionNEWS,news.bbc.co.uk/earth/hi/earth_news/newsid_8220000/8220636.stm, BBC, Axolotl verges on wild extinction, Matt Walker, 2009-08-26, 2010-06-28, WEB, PetAquariums.com, Are Axolotls Endangered? You Need To Be Carefulâ€¦,www.petaquariums.com/2020/10/21/are-axolotls-endangered-you-need-to-be-careful/, 2021-06-26, PetAquariums.com, 22 April 2020, en-US, 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). Axolotls are used extensively in scientific research due to their ability to regenerate limbs, gills and parts of their eyes and brains.VIDEO, 2009-11-11, Weird Creatures with Nick Baker, Television series, The Science Channel, Dartmoor, England, UK, 00:25, 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.JOURNAL, Sandoval-GuzmÃ¡n, Tatiana, August 2023, The axolotl,www.nature.com/articles/s41592-023-01961-5, Nature Methods, en, 20, 8, 1117â€“1119, 10.1038/s41592-023-01961-5, 37553398, 260699417, 1548-7091, Further research has been conducted to examine their heart as a model of human single ventricle and excessive trabeculation.JOURNAL, Meyer, Sophie, Lauridsen, Henrik, Pedersen, Kathrine, Andersson, Sofie Amalie, van Ooij, Pim, Willems, Tineke, Berger, Rolf M. F., Ebels, Tjark, Jensen, Bjarke, 2022-11-28, Opportunities and short-comings of the axolotl salamander heart as a model system of human single ventricle and excessive trabeculation, Scientific Reports, en, 12, 1, 20491, 10.1038/s41598-022-24442-9, 2045-2322, 9705478, 36443330, 2022NatSR..1220491M, Axolotls were also sold as food in Mexican markets and were a staple in the Aztec diet.NEWS, Mythic Salamander Faces Crucial Test: Survival in the Wild,www.nytimes.com/2012/10/31/world/americas/struggle-of-axolotls-mexicos-mythical-salamander.html?pagewanted=all&_r=1, 30 July 2015, The New York Times, 30 October 2012, Tickell, Sofia Castello Y., 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.JOURNAL, Malacinski, George M., American Zoologist, The Mexican Axolotl, Ambystoma mexicanum: Its Biology and Developmental Genetics, and Its Autonomous Cell-Lethal Genes, Spring 1978, 10.1093/icb/18.2.195, 18, 2, 195â€“206, free,

Description

(File:AxolotlBE.jpg|thumb|left|A captive leucistic axolotl, perhaps the most well known form of the axolotl)(File:Axolot’s head (Ambystoma mexicanum).jpg|thumb|Face of a common or wild type axolotl)File:Axolotl ganz.jpg|thumb|left|The speckled wild type wild type(File:Axolot’s_gills_(Ambystoma_mexicanum).jpg|thumb|Axolotl’s gills (Ambystoma mexicanum)|left)A sexually mature adult axolotl, at age 18â€“27 months, ranges in length from {{convert|15| to |45|cm|0|abbr=on}}, although a size close to {{convert|23|cm|0|abbr=on}} is most common and greater than {{convert|30|cm|abbr=on}} is rare. Axolotls possess features typical of salamander larvae, including external gills and a caudal fin extending from behind the head to the vent.San Francisco Examiner (San Francisco, California) 7 August 1887, page 9, authored by Yda Addis{{Citation|last1=McIndoe|first1=Rosemary|title=Functional morphology of gills in larval amphibians|date=1984|url=https://doi.org/10.1007/978-94-009-6536-2_4|work=Respiration and metabolism of embryonic vertebrates: Satellite Symposium of the 29th International Congress of Physiological Sciences, Sydney, Australia, 1983|pages=55â€“69|editor-last=Seymour|editor-first=Roger S.|series=Perspectives in vertebrate science|place=Dordrecht|publisher=Springer Netherlands|language=en|doi=10.1007/978-94-009-6536-2_4|isbn=978-94-009-6536-2|access-date=2021-05-13|last2=Smith|first2=D. G.}} External gills are usually lost when salamander species mature into adulthood, although the axolotl maintains this feature.BOOK, Kardong, Kenneth V,www.worldcat.org/oclc/1053847969, Vertebrates: comparative anatomy, function, evolution, 2019, McGraw-Hill Education, 978-1-259-70091-0, English, 1053847969, This is due to their neoteny evolution, where axolotls are much more aquatic than other salamander species.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. 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. 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.(File:Buccal pumping.jpg|thumb|428x428px|Buccal pumping)(File: Three Colors of Axolotl.jpg|thumb|right|Axolotls displaying variations in color)Axolotls have four pigmentation genes; when mutated, they create different color variants. The normal wild-type animal is brown or tan with gold speckles and an olive undertone. The five most common mutant colors are listed below.

Leucistic: pale pink with black eyes.
Xanthic: grey, with black eyes.
Albino: pale pink or white, with red eyes, which is more common in axolotls than other species.
Melanoid: all black or dark blue with no gold speckling or olive tone.

In addition, there is wide individual variability in the size, frequency, and intensity of the gold speckling, and at least one variant develops a black and white piebald appearance upon reaching maturity. WEB,exopetguides.com/axolotl/axolotl-colors/, 18 Types of Axolotl Colors You Can Own (Axolotl Color Guide), August 14, 2019, Because pet breeders frequently cross the variant colors, double homozygous mutants are common in the pet trade, especially white/pink animals with pink eyes that are double homozygous mutants for both the albino and leucistic trait.JOURNAL, Frost, Sally K., Briggs, Fran, Malacinski, George M., 1984, A color atlas of pigment genes in the Mexican axolotl (Ambystoma mexicanum), Differentiation, 26, 1â€“3, 182â€“188, 10.1111/j.1432-0436.1984.tb01393.x, Axolotls also have some limited ability to alter their color to provide better camouflage by changing the relative size and thickness of their melanophores.JOURNAL, 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, 37â€“60, 10.1016/0006-8993(85)90772-3, 4027646, 22723238,

Habitat and ecology

(File:Sunrise_in_Xochimilco_(Amanecer_en_Xochimilco)_2.jpg|thumb|Lake Xochimilco, Mexico City (Amanecer en Xochimilco). The native habitat of axolotls is important to the study of preservation and conservation. |left)(File:Axolotl Wild Type.jpg|thumb|left|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 {{convert|20|C|F}}, although it may fall to {{convert|6|-|7|C|F}} in the winter, and perhaps lower.WEB, Lake Xochimilco, Borough of Xochimilco in southern MÃ©xico City, 162 L â€¢ Biotope Aquarium,biotope-aquarium.info/aquariums/lake-xochimilco-borough-of-xochimilco-in-southern-mexico-city-162-l/, 2021-04-30, Biotope Aquarium, en-GB, Surveys in 1998, 2003, and 2008 found 6,000, 1,000, and 100 axolotls per square kilometer in its Lake Xochimilco habitat, respectively.WEB

, Stevenson, M.
, Mexico’s ‘water monster’ may have disappeared
, Associated Press, SFGate.com
, 2014-01-28
,www.sfgate.com/news/science/article/Mexico-s-water-monster-may-have-disappeared-5182823.php
, 2014-01-29, 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.NEWS,www.independent.co.uk/environment/axolotl-found-in-mexico-city-lake-after-scientists-feared-it-only-survived-in-captivity-9148775.html, Endangered ‘water monster’ Axolotl found in Mexico City lake, 2014-02-24, The Independent, 2017-06-02, en-GB,

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.NEWS,www.uswaternews.com/archives/arcglobal/8mexicity11.html, Mexico City’s ‘water monster’ nears extinction, November 2008, 2010-06-28, dead,www.uswaternews.com/archives/arcglobal/8mexicity11.html," title="web.archive.org/web/20110723194731www.uswaternews.com/archives/arcglobal/8mexicity11.html,">web.archive.org/web/20110723194731www.uswaternews.com/archives/arcglobal/8mexicity11.html, 2011-07-23, 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 speciesâ€”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|date=January 2017}}

Diet

The axolotl is carnivorous, consuming small prey such as mollusks,WEB,animaldiversity.org/accounts/Ambystoma_mexicanum/, Ambystoma mexicanum (Salamandra ajolote), Animal Diversity Web, worms, insects, other arthropods, 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.JOURNAL, 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, 329â€“341, 10.1159/000116519, 2611639,

Use as a model organism

{{See also|Model organism}}(File:Axolotl-2193331 1280.webp|thumb|right|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.JOURNAL, Gordon, R., 1985, A review of the theories of vertebrate neurulation and their relationship to the mechanics of neural tube birth defects,journals.biologists.com/dev/content/89/Supplement/229, Journal of Embryology and Experimental Morphology, 89, Supplement, 229â€“255, 3913733, There are also mutations affecting other organ systems some of which are not well characterized and others that are.JOURNAL, Armstrong, John B., 1985, The axolotl mutants, Developmental Genetics, 6, 1, 1â€“25, 10.1002/dvg.1020060102, The genetics of the color variants of the axolotl have also been widely studied.

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.JOURNAL, Caballero-PÃ©rez, Juan, Espinal-Centeno, Annie, Falcon, Francisco, GarcÃa-Ortega, Luis F., Curiel-Quesada, Everardo, Cruz-HernÃ¡ndez, AndrÃ©s, Bako, Laszlo, Chen, Xuemei, MartÃnez, Octavio, Alberto Arteaga-VÃ¡zquez, Mario, Herrera-Estrella, Luis, January 2018, Transcriptional landscapes of Axolotl (Ambystoma mexicanum), Developmental Biology, en, 433, 2, 227â€“239, 10.1016/j.ydbio.2017.08.022, 29291975, 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 brainâ€”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.JOURNAL, Roy, S, Gatien, S, Regeneration in axolotls: a model to aim for!, Experimental Gerontology, November 2008, 43, 11, 968â€“73, 18814845, 10.1016/j.exger.2008.09.003, 31199048, 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.JOURNAL, Vieira, Warren A., Wells, Kaylee M., McCusker, Catherine D., Advancements to the Axolotl Model for Regeneration and Aging, Gerontology, 2020, 66, 3, 212â€“222, 10.1159/000504294, 31779024, 7214127, free, 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.JOURNAL, Goodwin, James W., Pinto, Alexander R., Rosenthal, Nadia A., Eric N., Olson, Macrophages are required for adult salamander limb regeneration, Proceedings of the National Academy of Sciences of the United States of America, June 4, 2013, 110, 23, 9415â€“9420, 10.1073/pnas.1300290110, 23690624, 3677454, 2013PNAS..110.9415G, free, However, this belief has been questioned by other studies.JOURNAL, Pedersen, Katherine, Rasmussen, Rikke Kongsgaard, Dittrich, Anita, Pedersen, Michael, Lauridsen, Henrik, 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, April 17, 2020, 34, S1, 1, 10.1096/fasebj.2020.34.s1.04015, 218792957, free, 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.Masselink, Wouter, and Elly M. Tanaka. “Toward Whole Tissue Imaging of Axolotl Regeneration.” Developmental Dynamics, vol. 250, no. 6, 2020, pp. 800â€“806.,doi.org/10.1002/dvdy.282.

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.JOURNAL, Nowoshilow, Sergej, Schloissnig, Siegfried, Fei, Ji-Feng, Dahl, Andreas, Pang, Andy W. C., Pippel, Martin, Winkler, Sylke, Hastie, Alex R., Young, George, 2018-01-24, The axolotl genome and the evolution of key tissue formation regulators, Nature (journal), Nature, 554, 7690, 50â€“55, 10.1038/nature25458, 29364872, 1476-4687, 2018Natur.554...50N, free, 21.11116/0000-0003-F659-4, free, Although the axolotl genome is about 10 times as large as the human genome, it encodes a similar number of proteins, namely 23,251 (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.

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

, Ley
, Willy
, February 1968
, Epitaph for a Lonely Olm
, For Your Information,archive.org/stream/Galaxy_v26n03_1968-02_modified#page/n37/mode/2up
, Galaxy Science Fiction
, 95â€“104

, 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.JOURNAL, 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, 195â€“206, 10.1093/icb/18.2.195, free, The genes responsible have been narrowed down to a small chromosomal region called met1, which contains several candidate genes.JOURNAL, Crowner, Anne, Khatri, Shivam, Blichmann, Dana, Voss, S. Randal, Rediscovering the Axolotl as a Model for Thyroid Hormone Dependent Development, Frontiers in Endocrinology, 12 April 2019, 10, 237, 10.3389/fendo.2019.00237, free, 31031711, 6473073,

Metamorphosis

The axolotl’s 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, after which an axolotl undergoes an artificially-induced metamorphosis and begins living on land.JOURNAL, Demircan, Turan, Ovezmyradov, Guvanch, YÄ±ldÄ±rÄ±m, Berna, Keskin, Ä°lknur, Ä°lhan, AyÅŸe Elif, FesÃ§ioÄŸlu, Ece Cana, Ã–ztÃ¼rk, GÃ¼rkan, YÄ±ldÄ±rÄ±m, SÃ¼leyman, 2018-07-20, Experimentally induced metamorphosis in highly regenerative axolotl (Ambystoma mexicanum) under constant diet restructures microbiota, Scientific Reports, en, 8, 1, 10974, 10.1038/s41598-018-29373-y, 30030457, 6054665, 2018NatSR...810974D, In laboratory conditions, metamorphosis is reliably induced by administering either the thyroid hormone thyroxine or thyroid-stimulating hormone. The former is more commonly used.{{Side box|metadata=no|text=Role of iodineIn animals with functioning thyroid glands, iodine in the form of iodide is selectively gathered into the colloid of the thyroid. Inside the colloid, iodide is reduced to elemental iodine (I2), which reacts with the tyrosyl residues of thyroglobulin. Two iodinated tyrosyl residues are conjugated together. When they are cleaved from the thyroglobulin chain, thyroid hormone is obtained.Chapter 49, “Synthesis of Thyroid Hormones” in: BOOK, Walter F. Boron, Emile L. Boulpaep, Medical Physiology, 2nd, Elsevier/Saunders, 2012, 9781437717532, {{page needed|date=April 2016}}In the absence of induced metamorphosis, larval axolotls start absorbing iodide into their thyroid glands at 30 days postfertilization. Larval axolotls do produce thyroid hormone from iodide, but the amount appears highly variable. Adult axolotls do not produce thyroid hormone unless metamorphism is triggered.JOURNAL, Brown, Donald D., The role of thyroid hormone in zebrafish and axolotl development, Proceedings of the National Academy of Sciences, 25 November 1997, 94, 24, 13011â€“13016, 10.1073/pnas.94.24.13011, free, 9371791, 24254, 1997PNAS...9413011B, Diiodotyrosine, an analogue of the iodinated thyroglobulin precursor in thyroxine biosynthesis, causes metamorphosis in axolotls that have their thyroids removed.JOURNAL, Swingle, W. W., Iodine and Amphibian Metamorphosis, The Biological Bulletin, November 1923, 45, 5, 229â€“253, 10.2307/1536749, 1536749, Lugol’s solution, which contains both iodide and I2, triggers metamorphosis when injected.JOURNAL, Ingram, W. R., Metamorphosis of the Colorado Axolotl by Injection of Inorganic Iodine., Experimental Biology and Medicine, 1 December 1928, 26, 3, 191, 10.3181/00379727-26-4212, This is because diiodotyrosine and thyroxine is produced when I2 reacts with proteins other than thyroglobulin. If given in a bath instead of injected, I2 has no effect on axolotls.JOURNAL, Dvoskin, Samuel, The Thyroxine-Like Action of Elemental Iodine in the Rat and Chick1, Endocrinology, May 1947, 40, 5, 334â€“352, 10.1210/endo-40-5-334, 20245954, Iodide, which does not react with proteins, does not trigger metamorphosis. It does speed up the rate of metamorphosis, once it has been triggered by thyroid hormone extract.JOURNAL, Krylov, O. A., The role of haloids (bromine and iodine) in the metamorphosis of amphibia, Bulletin of Experimental Biology and Medicine, January 1961, 50, 1, 724â€“727, 10.1007/BF00796048, }}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.WEB, Axolotls - Metamorphosed & Tiger Salamanders,www.axolotl.org/tiger_salamander.htm, 2022-01-25, www.axolotl.org, An axolotl that has gone through metamorphosis resembles an adult plateau tiger salamander, though the axolotl differs in its longer toes.{{Citation needed|date=February 2011}} Among hobbyists, 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. Morphed pet axolotls should be given solid footholds in their enclosure to satisfy their need for land. They should not be given live animals as food.WEB, Transition & Feeding,www.morphedaxolotls.com/transition-and-feeding, Morphed Axolotls, en,

History

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 DumÃ©ril was surprised when, instead of the axolotl, he found in the vivarium a new species, similar to the salamander.{{verify source|reason=French language verification needed|date=November 2021}} 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|date=October 2021}} 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.JOURNAL, ReiÃŸ, Christian, Olsson, Lennart, HoÃŸfeld, Uwe, 2015, The history of the oldest self-sustaining laboratory animal: 150 years of axolotl research,onlinelibrary.wiley.com/doi/abs/10.1002/jez.b.22617, Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, en, 324, 5, 393â€“404, 10.1002/jez.b.22617, 25920413, 2015JEZB..324..393R, 1552-5015, Since then, experiments have been done often with injections of iodine or various thyroid hormones used to induce metamorphosis.JOURNAL, Safi, Rachid, Bertrand, StÃ©phanie, Marchand, Oriane, Duffraisse, Marilyne, de Luze, Amaury, Vanacker, Jean-Marc, Maraninchi, Marie, Margotat, Alain, Demeneix, Barbara, Laudet, Vincent, 2004-02-01, The Axolotl (Ambystoma mexicanum), a Neotenic Amphibian, Expresses Functional Thyroid Hormone Receptors, Endocrinology, 145, 2, 760â€“772, 10.1210/en.2003-0913, 14576183, free,

In other salamanders

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.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.WEB, Venturi, S., 2004,sites.google.com/site/iodinestudies/morosini, 4 March 2017, dead,web.archive.org/web/20170304010444/https://sites.google.com/site/iodinestudies/morosini, 25 September 2020, Iodine and Evolution. DIMI-Marche, 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.(File:Lake Xochimilco in Southern Mexico.jpg|thumb|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.JOURNAL, Nandini, Sarma, GarcÃa, Pedro Ramirez, Sarma, S. S. S., 2016, Water quality in Lake Xochimilco, Mexico: zooplankton indicators and Vibrio cholerae,www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2015.1213, Journal of Limnology, en, 75, 1, 10.4081/jlimnol.2015.1213, 1723-8633, free, 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.JOURNAL, Robles-Mendoza, C., GarcÃa-Basilio, C., Cram-Heydrich, S., HernÃ¡ndez-Quiroz, M., Vanegas-PÃ©rez, C., 2009-02-01, Organophosphorus pesticides effect on early stages of the axolotl Ambystoma mexicanum (Amphibia: Caudata),www.sciencedirect.com/science/article/pii/S004565350801223X, Chemosphere, en, 74, 5, 703â€“710, 10.1016/j.chemosphere.2008.09.087, 19012946, 2009Chmsp..74..703R, 0045-6535, 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.JOURNAL, Alcaraz, Guillermina, LÃ³pez-Portela, Xarini, Robles-Mendoza, Cecilia, 2015-07-01, Response of a native endangered axolotl, Ambystoma mexicanum (Amphibia), to exotic fish predator,doi.org/10.1007/s10750-015-2194-4, Hydrobiologia, en, 753, 1, 73â€“80, 10.1007/s10750-015-2194-4, 254550469, 1573-5117, 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.JOURNAL, Parra-Plea, G, Zamudio, K.R., Recuero, E., Aguilar-=Miguel, X., Huaxuz, D., Zambrano, L., 2011, Conservation genetics of threatened Mexican axolotls (Ambystoma),doi.org/10.1111/j.1469-1795.2011.00488.x, American Conservation, 15, 1, 61â€“72, 10.1111/j.1469-1795.2011.00488.x, 46992721, The detection of introgressed tiger salamander (A. tigrinum) DNA in the laboratory axolotl population raises further concerns about the suitability of the captive population as an ark for potential reintroduction purposes.JOURNAL, Woodcock, M. Ryan, Vaughn-Wolfe, Jennifer, Elias, Alexandra, Kump, D. Kevin, Kendall, Katharina Denise, Timoshevskaya, Nataliya, Timoshevskiy, Vladimir, Perry, Dustin W., Smith, Jeramiah J., Spiewak, Jessica E., Parichy, David M., Voss, S. Randal, 2017-01-31, Identification of Mutant Genes and Introgressed Tiger Salamander DNA in the Laboratory Axolotl, Ambystoma mexicanum, Scientific Reports, en, 7, 1, 6, 10.1038/s41598-017-00059-1, 28127056, 2045-2322, 5428337, 2017NatSR...7....6W, 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.JOURNAL, Ramos, A.G., Mena-Gonzalez, H., Zambrano, L, 2021, The potential of temporary shelters to increase survival of the endangered Mexican axolotl,doi.org/10.1002/aqc.3520, Aquatic Conservation: Marine and Freshwater Ecosystems, 31, 6, 1535â€“1542, 10.1002/aqc.3520, 2021ACMFE..31.1535R, 235587173, NEWS, PaÃºl, MarÃa Luisa, 2023-12-01, Mexico wants you to adopt an axolotl, the amphibian that never grows up, en-US, Washington Post,www.washingtonpost.com/nation/2023/12/01/axolotl-mexican-salamander-adoption-campaign/, 2023-12-01, 0190-8286,

Captive care

{{See also|Herpetoculture}}File: Ambystoma mexicanum at Vancouver Aquarium.jpg|thumb|left|These axolotls at Vancouver Aquarium are leucistic leucistic(File:Axolotl in a Pet store in Melbourne.jpg|thumb|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 {{convert|16|C|F}} to {{convert|18|C|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 {{convert|24|C|F}} may lead to metabolic rate increase, also causing stress and eventually death.WEB,www.axolotl.org/requirements.htm, Axolotls â€“ Requirements & Water Conditions in Captivity, axolotl.org, 2016-03-14, WEB,www.caudata.org/cc/species/Ambystoma/A_mexicanum.shtml, Caudata Culture Species Entry â€“ Ambystoma mexicanum â€“ Axolotl, www.caudata.org, 2016-03-14, 2016-03-15,www.caudata.org/cc/species/Ambystoma/A_mexicanum.shtml," title="web.archive.org/web/20160315031956www.caudata.org/cc/species/Ambystoma/A_mexicanum.shtml,">web.archive.org/web/20160315031956www.caudata.org/cc/species/Ambystoma/A_mexicanum.shtml, dead, Chlorine, commonly added to tapwater, is harmful to axolotls. A single axolotl typically requires a {{convert|150|L|gal|adj=on|abbr=off}} tank. Axolotls spend the majority of the time at the bottom of the tank.WEB,www.tfhmagazine.com/articles/freshwater/axolotls-keeping-a-water-monster-full, Wiegert, Joshua, Axolotls: Keeping a Water Monster, (File: Axolotl with Grit XRay.png|thumb|upright=0.6|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.JOURNAL, Kulbisky, Gordon P, Rickey, Daniel W, Reed, Martin H, BjÃ¶rklund, 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, 969â€“975, 10.1016/s0301-5629(99)00040-x, 10461726, )Salts, such as Holtfreter’s solution, are often added to the water to prevent infection.WEB, Clare, John P.,www.axolotl.org/health.htm, Health and Diseases, axolotl.org, 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.JOURNAL, 10.1577/03632415.2011.10389070, The Aquarium Trade as an Invasion Pathway in the Pacific Northwest, Fisheries, 36, 2, 74â€“85, 2011, Strecker, Angela L., Campbell, Philip M., Olden, Julian D., 2011Fish...36...74S,pdxscholar.library.pdx.edu/esm_fac/40, Substrates are another important consideration for captive axolotls, as axolotls (like other amphibians and reptiles) tend to ingest bedding material together with food and are commonly prone to gastrointestinal obstruction and foreign body ingestion.JOURNAL, Amphibian Emergency Medicine, Veterinary Clinics of North America: Exotic Animal Practice, 10, 2, 587â€“620, 10.1016/j.cvex.2007.02.004, 17577564, 2007, Clayton, Leigh Ann, Gore, Stacey R., 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.WEB, Pough, F. H.,netvet.wustl.edu/species/reptiles/pough.txt, Recommendations for the Care of Amphibians and Reptiles in Academic Institutions, National Academy Press, Washington, D.C., 1992, 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.JOURNAL, Gresens, Jill, An Introduction to the Mexican Axolotl (Ambystoma mexicanum), Lab Animal, 33, 9, 2004, 41â€“47, 10.1038/laban1004-41, 15457201, 33299160, There is some evidence that axolotls might seek out appropriately-sized gravel for use as gastrolithsWings, O A review of gastrolith function with implications for fossil vertebrates and a revised classification Acta Palaeontologica Polonica 52 (1): 1â€“16 based on experiments conducted at the University of Manitoba axolotl colony,Gordon, N, Gastroliths â€“ How I Learned to Stop Worrying and Love Gravel.BjÃ¶rklund, 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: 38â€“47. 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.JOURNAL, Loh, Richmond, 2015-05-15, Common Disease Conditions in Axolotls, Vin.com,www.vin.com/apputil/content/defaultadv1.aspx?pId=14365&catId=73681&id=7259254, live, 2022-01-21,web.archive.org/web/20200804110231/https://www.vin.com/apputil/content/defaultadv1.aspx?pId=14365&catId=73681&id=7259254, 2020-08-04,

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.NEWS, 2018-11-20, Mexico’s axolotl, a cartoon hero and genetic marvel, fights for survival, en, Reuters,www.reuters.com/article/us-mexico-axolotl-idUSKCN1NP0F6, 2022-08-16, AxÃ³lotl 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.WEB, 2020-02-21, Mexican axolotl will be the new image of the 50 peso bill,www.theyucatantimes.com/2020/02/mexican-axolotl-will-be-the-new-image-of-the-50-peso-bill/, 2020-03-04, The Yucatan Times, en-US, WEB, Billete de 50 pesos de la familia G,www.banxico.org.mx/billetes-y-monedas/billete-50-pesos-familia-g.html, 2023-02-20, www.banxico.org.mx, es, It was recognized as “Bank Note of the Year” by the International Bank Note Society.WEB, Banknote of 2021 Nominations,www.theibns.org/joomla/index.php?option=com_content&view=article&id=809:banknote-of-2021-nominations&catid=39:banknote-of-2021&Itemid=51, 2023-02-20, www.theibns.org, HD 224693, a star in the equatorial constellation of Cetus, was named AxÃ³lotl in 2019.WEB, Approved names,www.nameexoworlds.iau.org/final-results, 2020-01-02, www.nameexoworlds.iau.org, en, WEB, December 17, 2019, 100 000s of People from 112 Countries Select Names for Exoplanet Systems In Celebration of IAU’s 100th Anniversary,www.iau.org/news/pressreleases/detail/iau1912/, 2020-01-02, International Astronomical Union, The PokÃ©mon Mudkip and its evolutions, added in PokÃ©mon Ruby and Sapphire (2002), take some visual inspiration from axolotls. Additionally, the Pokemon Wooper, added in PokÃ©mon Gold, Silver and Crystal (1999), is directly based on an axolotl.{{Additional citation needed|date=May 2023}} The looks of the dragons Toothless and The Night Fury in the How to Train Your Dragon movies are based on axolotls. 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.WEB, Minecraft, October 3, 2020, “Minecraft Live: Caves & Cliffs - First Look”,www.youtube.com/watch?v=DBvZ2Iqmm3M&t=2486s, YouTube, “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, They were also added to its spin-off (Minecraft Dungeons|Minecraft: Dungeons) in 2022 and are available in Lego Minecraft.WEB, The Guardian Battle 21180,www.lego.com/en-us/product/the-guardian-battle-21180, 2023-02-20, www.lego.com, en, An anthropomorphic Axolotl named Axo was also added as a purchasable outfit in Fortnite Battle Royale on August 9, 2020.WEB, 5 August 2020, Fortnite v13.40 Leaked Skins: Axo, Castaway Jonesy, Crustina & More,culturedvultures.com/fortnite-v13-40-leaked-skins-axo-castaway-jonesy-crustina/, TWEET, 1425245581480448005, FortniteGame, Axo got a new style just in time for @maisie_williams & @reubenSelby’s hand-picked Locker Bundle,

References

External links

{{Curlie|Science/Biology/Flora_and_Fauna/Animalia/Chordata/Amphibia/Caudata/Ambystomatidae/|Ambystomatidae}}
www.fishtankforum.co.uk/forum/viewtopic.php?f=190&t=5263" title="web.archive.org/web/20160805192629www.fishtankforum.co.uk/forum/viewtopic.php?f=190&t=5263">Follow the Eggs, Hatchlings and Juveniles
fishtankforum.co.uk/forum/viewtopic.php?f=190&t=6455" title="web.archive.org/web/20160310105933fishtankforum.co.uk/forum/viewtopic.php?f=190&t=6455">Mating Dance and Laying Eggs
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www.biologydir.com/indiana-university-axolotl-colony-info-11384.html" title="web.archive.org/web/20140517152123www.biologydir.com/indiana-university-axolotl-colony-info-11384.html">Indiana U Axolotl Colony
University of KY Axolotl Colony
Mystical amphibian venerated by Aztecs nears extinction
The animal that’s everywhere and nowhere
EB1911, Axolotl, 20, 63, x,

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