With its captivating wide-mouthed smile and prominent feathery headdress of gills, it is easy to adore the axolotl (Ambystoma mexicanum). Both salamander enthusiasts and scientists acknowledge the utility of these unique aquatic creatures. Axolotls are wizards of regeneration, a trait that is recognized by biomedical researchers across the globe. A PubMed query for ‘axolotl’ returns more than 3400 results, with recent publications in high impact journals such as Cell and Nature. As axolotls are picking up steam as model organisms, they’re also becoming quite popular in the homes of several CAMB graduate students who share a love for these unique creatures.
The axolotl’s name is deeply rooted in Aztec mythology and according to legend, Xolotl, the god of death and lightning, morphed into an axolotl to avoid being killed by other gods. Axolotls can live up to 15 years in the wild and can grow up to an impressive 12 inches in length. Interestingly, axolotls retain larval features, like their feathery external gills and tadpole-like tails, well into adulthood, and are solely aquatic even at sexual maturity. These one-of-a-kind salamanders really are just that; found exclusively in lake Xochimilco in southern Mexico City, axolotls are currently listed as a critically endangered species, as their population continues to decline. Wild axolotls face many threats to their habitat including widespread water pollution and lake drainage. Lake Xochimilco has also recently become the site of large-fish farming, which comes at the expense of axolotls. These large tilapia and carp compete with axolotls for resources and eat axolotl eggs. Another lesser-known reason for their population decline is that axolotls are considered a delicacy when roasted and are rumored to taste like a cross between a fish and a chicken.
Although axolotls face significant challenges in the wild, they are thriving in captivity. Possessing prodigal regenerative abilities, axolotls are no strangers to the laboratory as they have been used in research since 1864. Compared to other salamanders, axolotls are easy to breed and their large embryos are easily manipulated. Perhaps the biggest draw of using axolotls as a model organism is that they can recover from an incredible amount of injury. Axolotls faithfully regenerate entire limbs, and can do so without scarring, even after repeated removal of the same limb. Researchers can crush or remove a segment of the spinal cord and it will still regenerate. The list of regenerative body parts is virtually endless and includes limbs, tail, jaw, and parts of many vital organs such as the brain and heart. Intriguingly, an axolotl can also accept transplanted organs without rejection, and future studies may uncover insights for preventing graft rejection in transplant recipients.
Not all axolotl science is so Frankensteinian in nature. Researchers these days are also engaged in experiments using the latest cutting-edge technologies to better understand regeneration. In a manuscript published in Cell Reports in early 2017, scientists at Harvard assembled 88% of the axolotl genome and used this assembly to perform RNA-Seq to identify conserved genes involved in limb outgrowth. Researchers in Germany created transgenic brainbow-labeled axolotls to perform live-imaging based lineage tracing in a Developmental Cell paper from 2016. This powerful tool was used to examine the dynamics of cellular recruitment and migration during limb regeneration. These and other recent studies demonstrate the power of the axolotl as a model organism, and researchers hope that these seminal discoveries will advance the field of mammalian regeneration to recreate the phenomenon in humans.
It’s no wonder that axolotls are also popular pets in the homes of several CAMB-DSRB students. These always smiley and ever-regenerating creatures are easy to care for in captivity and are quite happy as long as the water flow, temperature, and quality are well controlled. As carnivores, axolotls most commonly consume frozen cubes of bloodworms, but they also enjoy pieces of cooked shrimp and other meats as special treats. Axolotls are quite voracious and, if left hungry, will not hesitate to resort to cannibalism. Most axolotls are also perfectly happy living alone so, to avoid undue stress and epic fish carnage, some prefer to house their axolotls in separate tanks. Unfortunately these little guys aren’t always the smartest and may try to eat anything smaller than their own head. For this reason, avoid pebbles in axolotl tanks and use sand instead. Finally, as their hearty appetite predicts, axolotls are excretory machines and keeping up with waste removal and water cleaning is a must for a stress-free animal.
Graduate student Ben Tajer (DSRB), the reigning axolotl expert of CAMB, is no stranger to raising salamanders. After fortuitously stumbling upon an abandoned 40-gallon aquarium in Clark Park, he ordered axolotl eggs for both himself and to share with friends, plus extras (50 to be exact). Ben currently hosts an impressive cast of axolotl characters named Glompner, Blumpus, Flumpus, TeeneeMeenee, Cousin Melvis, and Chompner. But don’t be fooled by their smiling faces. Ben says, “I look into my axolotls' eyes and I see pure murder. They are relaxed most of the time, but when they notice me near the aquarium they will come to the side and start attacking each other in anticipation of food. They eat the blood worm cubes before they melt, and I have had to isolate the particularly violent ones.” In particular, Chompner has perfected a technique for twisting arms off the other axolotls and is now in solitary confinement.
Not all axolotls are bloodthirsty, and they can be great friends, too. Robyn Allen (VMD/DSRB) owns Lancelotl (Lance) and Camelotl (Cam) that tend to hang out next to each other and have even burrowed a nest into the sand together. Some CAMB-ers prefer to own a single axolotl. Will Towler (DSRB) describes Morty’s (aka Baby Mort-Mort) personality as “similar to a rock, but timid.” Morty is still getting the hang of the whole eating thing. During feeding he “swims to the surface of his tank, attacks the air, realizes the empty atmosphere itself wasn't the brick of food he thought it was, and gives up, only to finally eat once food is falling directly on his face” says Will. Ernest Monahan (DSRB) shares that his axolotl Poseidon, who also happens to be a polydactyl, will “usually ignore my existence unless it becomes too hungry.”
The endearing perma-smile, Pokémon-esque looks, and occasional lapse of intelligence have clearly won over the hearts of CAMB students, and axolotls have become wonderful companions for some. Ben says that the best part about being an axolotl owner is “watching them grow and change”.
If you are interested in adopting a wild type axolotl of your own, contact Ben Tajer for more information. Axolotls will only be given to those with proper knowledge of axolotl care and housing