The axolotl, Ambystoma mexicanum, is a type of salamander defined by its natural state of neoteny, retaining its aquatic characteristics throughout its adult life. It reaches sexual maturity while keeping features like external gills and a finned tail. Metamorphosis, the process of transforming into a land-dwelling salamander, is an extremely rare occurrence in nature for the axolotl. The resulting terrestrial form differs significantly from its aquatic state.
Triggering the Transformation
The axolotl’s ability to remain in its larval state is primarily due to a deficiency in the production of thyroid-stimulating hormone (TSH), which leads to low levels of the thyroid hormone, thyroxine (T4). While axolotl tissues are fully capable of responding to this hormone, the animal does not produce enough of it naturally to initiate metamorphosis. The rare instances of natural metamorphosis are often attributed to extreme environmental stressors, such as rapidly deteriorating water quality, high temperatures, or water levels that are suddenly too low.
The process is most commonly induced in laboratory settings by administering thyroxine or a thyroid-stimulating hormone. Injecting thyroxine will trigger a full transformation, with younger animals completing the process in about two weeks. The goal of artificial induction is to bypass the animal’s genetic suppression and force the developmental changes necessary for a transition to land.
Life Without Gills: Morphological Changes
The change from an aquatic to a terrestrial form involves physical and physiological modifications. One of the most noticeable changes is the retraction and eventual absorption of the feathery external gills, which are no longer needed for underwater respiration. Simultaneously, the dorsal and caudal fins, used for propulsion in water, recede and disappear. The tail itself becomes thinner, taking on a more rounded, lizard-like appearance suitable for terrestrial locomotion.
Internally, the axolotl’s rudimentary lungs undergo significant development, becoming much more effective for gas exchange and air breathing. The skin thickens and darkens, losing the delicate slime coat needed for aquatic life and becoming less permeable to water, which helps prevent dehydration on land. The eyes, which were previously flat and lidless, begin to bulge and develop functional eyelids. The limbs also strengthen and the bones change shape to better support the animal’s body weight against gravity.
Terrestrial Care Requirements
Once the metamorphosis is complete, the animal is no longer an aquatic species and requires a shift in its habitat to a terrestrial or semi-aquatic setup. The most appropriate enclosure is a terrarium, which must maintain high humidity levels, often between 70% and 80%, to prevent the new skin from drying out. The substrate should be a deep, loose material like sterile potting soil, coco fiber, or peat moss, allowing the animal to burrow for comfort and moisture. The enclosure temperature should be kept relatively cool, ideally between 14 and 24 degrees Celsius (57 to 75 degrees Fahrenheit), as the animal does not tolerate high heat.
A shallow water dish is still necessary, allowing the transformed salamander to soak when needed, though the water level must be low enough for easy exit. The diet must change from aquatic prey to terrestrial invertebrates, as the transformed animal hunts differently on land. Common food sources include gut-loaded crickets, earthworms, and various insect larvae. Because the animal relies on movement to detect its prey, live food is generally required.
Longevity and Health Concerns
The transformation process places stress on the axolotl’s system, often leading to long-term health consequences. While a neotenic axolotl can live for 10 to 15 years, and sometimes longer in captivity, an artificially metamorphosed specimen typically has a much shorter lifespan. Many transformed axolotls scarcely survive past five years of age. The process of metamorphosis involves breaking down and rebuilding many organ systems, which can severely compromise the immune system and increase susceptibility to disease.
The extensive physiological changes, particularly when forced, often result in a decline in the animal’s remarkable regenerative abilities. Furthermore, the resulting terrestrial form often retains some genetic deficiencies or structural issues that make it less robust than naturally terrestrial salamanders.