(Image via animals.sandiegozoo.org) 

Volunteer Writer: Emma Bowser

Email: ebowser@umassd.edu 

Axolotls (Ambystoma mexicanum) have always fascinated people, even if it seems like their popularity sprung up out of nowhere. Biologists have studied axolotls for about 150 years since they were first imported to France from Mexico in 1864. 

Originally, they were used for more general research purposes and were often treated as a novelty in Europe. After they were spread across the continent, people started to examine their unique anatomy, study how they metamorphosed, and were used in arguments for and against Darwinism.

Now they’re everywhere in pop culture. You can find them on school supplies, water bottles, Girl Scout patches, and even in pet stores. It’s theorized that Minecraft brought them back into the public’s view, but it appears that their most recent claim to fame has to do with their aging process.

Axolotls are unusual creatures because they have a surprisingly short lifespan for a species of salamander yet maintain their physical functions and have a resistance to cancer even when directly injected with carcinogens.

They are of particular interest to scientists because of this, and many studies have been conducted to determine what exactly makes the axolotl so different from other species and if that factor (or a combination thereof) could be replicated and used on other species, such as humans. 

In short, the axolotl’s remarkable ability to avoid the negative physiological effects of aging and grow back limbs and/or internal organs that were removed makes it the perfect candidate for studies focused on expanding the human lifespan and changing the field of medicine as we know it.

A research team studying this published a preprint of their findings on September 10th, 2024. Because it is a preprint, it is not peer-reviewed yet, but the data is promising. 

The research team analyzed the epigenetic clocks of axolotls to learn more about how they age (or don’t age). They discovered that the clocks are biphasic, capable of predicting age during early life but not for the rest of their lifespan. 

Thus, after the second phase has started, scientists cannot calculate an axolotl’s age, while they would be able to calculate the age of a human or other living organism. This property means that the axolotl has been added to the list of species that have negligible senescence. 

Other species exhibiting negligible senescence include some varieties of fish, tortoises, and turtles. Some trees, such as aspens and pines, are also thought to have negligible senescence, with some individuals theorized to have lived thousands of years. Certain strains of bacteria also show negligible senescence.

Other extraordinarily long-lived species are usually considered to go through the cryptobiosis process or have negative senescence and essentially age in reverse.

However, one thing that really sets the axolotl apart from other species that experience negligible senescence is how genetically stable they remain, even during parts of the process when they weren’t expected to be, which implies that this species deviates from known patterns of epigenetic aging. 

Another important detail is how the axolotls were shown to be able to rejuvenate parts of their body if they were regenerated. When the scientists removed a body part, such as a limb or internal organ, they noticed that sometimes the new body parts that the axolotl grew were younger than the ones that they had removed.

While scientists are aware of the axolotl’s ability to regenerate body parts, and even regenerate the same body part several times, they didn’t expect it to cause small amounts of negative senescence as a side effect of that process.

You can read the preprint of this study here if you’re interested. You can read more general information about axolotls and their status as a critically endangered species here.