Axolotls Lose Their Superpower When They Transform Into Land-Dwelling Adults

We examined one of the most compelling questions in evolutionary biology: why some animals can regenerate injured structures while others cannot.

We synthesized decades of research across the animal kingdom, looking for patterns that might explain the patchy distribution of regenerative ability. What emerged was a complex picture where regeneration isn't simply present or absent, but varies in degree and changes throughout an animal's life. Within single species, regenerative capacity often declines with age and body size, or can be lost entirely during major life transitions.

One striking example comes from axolotls, the famous regenerating salamanders. These animals can regrow limbs, tails, and even parts of their hearts and brains. But when axolotls undergo metamorphosis and transform into their terrestrial adult form, they lose much of this regenerative capacity. This observation suggests that the traits enabling regeneration may be incompatible with other physiological demands of adult life.

"One striking example comes from axolotls, the famous regenerating salamanders."

We found that smaller body size and higher metabolic rates often correlate with greater regenerative capacity. This relationship hints at possible trade-offs between regeneration and other energetically costly processes like growth and reproduction. Animals investing heavily in rapid reproduction, for instance, may have fewer resources available for maintaining regenerative machinery.

These patterns raise provocative questions about human regeneration. Humans retain some regenerative capacity, being able to heal wounds and regenerate liver tissue, but cannot regrow limbs. Understanding what molecular and cellular mechanisms have been lost or suppressed could potentially inform medical approaches to enhance tissue repair.

The review also highlighted how much remains unknown. Why did some lineages lose regeneration while closely related species retained it? What specific genes and developmental pathways control this ability? As genetic tools become more powerful, researchers may be able to answer these questions and perhaps one day unlock latent regenerative potential in species, including humans, that have lost this remarkable ability.

Citation

Seifert, Ashley W.; Monaghan, James R.; Smith, Matthew D.; Pasch, Bret; Stier, Adrian C.; Michonneau, François; Maden, Malcolm (2012). The influence of fundamental traits on mechanisms controlling appendage regeneration. Biological Reviews.

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