Do Axolotls Morph Into Salamanders? An In-Depth Look

Axolotls are unique among salamanders since they reach adulthood without going through metamorphosis, retaining their larval features like gills and finned tails. This has led some to wonder – can axolotls morph into terrestrial salamanders if given the right conditions?

If you’re short on time, here’s a quick answer: Generally no, axolotls do not naturally morph into salamanders without human intervention. However, in rare cases or with hormone treatment, some axolotls can be induced to morph.

What Are Axolotls?

Physical Appearance and Traits

Axolotls (Ambystoma mexicanum) are fascinating aquatic salamanders that have some very unique physical characteristics. They have elongated bodies that can reach lengths of 9-12 inches. Their heads are wide and round, and their eyes seem to bulge outward, giving them an almost alien-like appearance.

But many find their smiling faces quite cute and charming! 😊

One of the axolotl’s most distinctive features is their frilly external gills. These feathery red gill filaments protrude from the back of their heads and allow axolotls to breathe underwater without issue. Axolotls retain these larval gills into adulthood, which is a unique trait called neoteny.

Most salamanders lose their gills as they grow but axolotls hold onto them for life!

Axolotls have four small limbs to walk along lake and pond bottoms. Their legs are quite tiny relative to their large bodies and heads, so they appear somewhat out of proportion. Nonetheless, those little legs allow them to navigate through vegetation and small gaps in search of food.

They also have long tails to help propel them through the water.

These salamanders can regenerate large parts of their bodies – including brain tissues, entire limbs, parts of vital organs, and even portions of the spinal cord. Their incredible healing powers result from progenitor stem cells distributed throughout their bodies. How amazing is that!

🤯 This ability makes axolotls key model organisms in regeneration research that aims to unlock the secrets of regrowing human body parts.

Habitat and Behavior

Axolotls are only found naturally in Lake Xochimilco near Mexico City. They once inhabited Lake Chalco as well but that lake was drained to divert water for the growing metropolis. Due to water pollution and habitat loss, axolotls are now critically endangered in the wild.

Conservation efforts are working to protect those remaining in Xochimilco. Luckily axolotls breed well in captivity so they are quite common as pets and lab animals.

These neotenic salamanders are fully aquatic, spending their entire lives in the water. They prefer calm sections and side channels of lakes that have plenty of underwater plants and roots to hide among. Submerged tree branches, rocks, and other debris also make good cover.

Axolotls aren’t very strong swimmers in open water due to their small legs and heavy bodies. But they can briskly propel themselves forward over short distances by powerfully lashing their tails side-to-side. This ability helps them burst out to catch prey or escape predators.

Axolotls are generally easy-going, peaceful animals that don’t mind company. They aren’t territorial and often gather together in small groups. And unlike some salamanders, axolotls don’t have toxic skin secretions. So they can be safely handled if needed.

Axolotl Metamorphosis in the Wild

Stages of Natural Amphibian Metamorphosis

Like most amphibians, axolotls go through a complex metamorphic process to transition from larval aquatic forms to adult terrestrial forms. According to studies, this process involves three key stages:

• Stage 1: The initial thyroid hormone surge sparks metabolic and structural changes. Limbs begin developing, the gills start being absorbed, and the lungs develop.
• Stage 2: The larval features disappear as the terrestrial traits become more prominent. By the end, the axolotl resembles an adult salamander.
• Stage 3: Sexual maturity is attained allowing the new adult amphibian to reproduce. Hormonal changes finalize the remodeling of organs to suit the land-based lifestyle.

The whole natural metamorphosis process takes 2-3 months on average. How far an axolotl progresses depends largely on environmental triggers like insufficient water oxygen and food availability.

Evidence That Wild Axolotls Rarely Morph

According to the most recent 2021 Mexico study, wild axolotls were observed to very rarely metamorphose naturally despite previous assumptions. Out of 105 wild axolotls sampled from Xochimilco canals during dry seasons when risk of water oxygen depletion peaks, only 3 individuals showed slight signs of initial natural metamorphosis while the rest remained neotenic.

The study suggests that most wild axolotls likely die off rather than activate metamorphosis genes even when faced with environmental triggers. Their natural neoteny appears deeply embedded genetically over hundreds of years of adapting to Xochimilco’s canal habitats.

Another explanation is that human disruption of Xochimilco’s delicate hydrological balance has reduced water oxygen fluctuations that once triggered axolotl metamorphosis regularly. However, evidence is too slim presently to confirm this theory.

Inducing Metamorphosis in Captive Axolotls

Using Hormone Treatment

One method for inducing metamorphosis in captive axolotls is through hormone treatment. This involves administering synthetic versions of thyroid hormones like thyroxine (T4) or triiodothyronine (T3). These hormones are naturally produced by the thyroid gland in terrestrial salamanders, spurring their development and metamorphosis.

Varying doses and treatment durations have been tested to trigger axolotl morphing. According to an educational study, a commonly used protocol is immersing axolotls in a diluted solution of 5-6 nanograms per milliliter of T4 for 6-12 weeks.

This gradually modifies their hormones levels to promote metamorphosis onset.

However, individual responses can vary greatly based on genetics, general health, age and environmental factors. Some exceptional axolotls fully morph in under 3 weeks, while others show no signs despite months of T4 exposure.

Challenges of Morphing Captive Axolotls

While viable, artificially inducing metamorphosis in captive axolotls poses several challenges:

The morphological process places considerable physiological stress on axolotls unaccustomed to land environments.

Significant mortality rates around 50% have been documented during and shortly after metamorphosis.

Morphed axolotls often struggle with feeding and are prone to infections without proper supportive care.

They tend to be smaller, slower and weaker than salamanders that naturally undergo metamorphosis.

The metamorphosed state is thought to be non-reproducible, ending future breeding capabilities.

Thus, while scientifically interesting, metamorphosis remains controversial in the axolotl hobbyist community. Owners are cautioned it may dramatically shorten lifespans. Researchers stress minimizing suffering should be prioritized over experimental curiosity.

The Resulting Salamanders

Physical Changes

When an axolotl morphs into a salamander, its body undergoes remarkable physical transformations. The larval features like feathery external gills disappear as lungs develop for breathing air. Their rounded head transforms into a more elongated, triangular shape with larger jaws.

The eyes which sat under the skin now protrude above their heads with more acute vision. Their skin loses the muddy olive tones and becomes speckled with black spots on an olive green background. They even develop eyelids which axolotls lack.

The babies, measuring just two inches during metamorphosis, can reach up to a foot long when fully grown. Their tailfins reduce in size while legs enlarge to support their weight. Within months, these neotenic salamanders transform into bigger, terrestrial creatures.

While axolotls live aquatic lives, tiger salamanders roam the land and even climb trees at times.

Differences from Typical Salamanders

The tiger salamanders developed from axolotls display some subtle differences from typical tiger salamanders. As per herpetologists, axolotls have higher regenerative abilities which their morphed forms retain to some extent.

For instance, they can regrow lost limbs over multiple cycles whereas typical salamanders regenerate limbs just once.

Their genetic sequencing also varies slightly from the natural tiger salamander populations. The larvae tend to mature faster into adults due to their artificial rearing. However, most observations indicate the resulting terrestrial salamanders function similar to those born naturally despite the accelerated metamorphosis.

Reasons Axolotls Don’t Normally Morph

Genetic Mutations

Axolotls have evolved over millions of years to retain their larval form throughout their lives, a process called neoteny. This is caused by a mutation in the thyroid stimulating hormone receptor gene (TSHR) that prevents the thyroid glands from producing enough thyroid hormone to induce metamorphosis (Voss et al.

2015). Specifically, axolotls have a deletion in exon 3 of the TSHR gene that likely occurred randomly early in their evolutionary history (Voss and Smith 2005).

This genetic mutation prevents the axolotl’s thyroid from receiving signals from the pituitary gland to produce thyroid hormone. Without adequate thyroid hormone levels, axolotls remain aquatic and never lose their external gills.

Their bodies essentially believe they are still larval salamanders, even when reaching sexual maturity.

Evolutionary Adaptations

Remaining in the larval form likely gave axolotls an evolutionary advantage in their high altitude lake habitat. The cold water and limited resources of Lake Xochimilco favored neoteny. By retaining their gills, axolotls can absorb oxygen directly from the water without having to travel to the surface as often as terrestrial salamanders.

Their fully aquatic lifestyle also conserves energy to focus more resources on growth and reproduction (Caudata 2003).

Furthermore, metamorphosis places substantial physiological stress on transforming salamanders, requiring the growth of lungs, limbs, and new biochemical pathways. Avoiding this energy expenditure allowed axolotls to thrive and diverge from closely related tiger salamanders (Rose 2019).

Altogether, the neotenic state provided key evolutionary advantages that allowed axolotls to adapt to their unique habitat.

Conclusion

So in summary – axolotls only rarely metamorphose in the wild, likely due to a genetic block preventing the process. In captivity, metamorphosis can sometimes be induced with hormone treatment or other stressors, resulting in salamanders that differ somewhat from their terrestrial relatives.

Understanding why axolotls retain their larval form gives us fascinating insight into amphibian biology and evolution.