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Regeneration is central to life and every animal is capable of it at the small scale of cells and tissues. Some animals take this much further: the hydra flatworm, for example, can remodel whole sections of itself; if you cut one in half, you end up with two.
Caudata, the order of tailed amphibians which includes newts, is probably the most adept vertebrate group at regeneration. They can regenerate tails, limbs, internal structures, and apparently even eyes! Autotomy (self amputation), is a defensive action seen in geckos, lizards and some salamanders. It allows them to drop tails or limbs when threatened by a predator. After the tail or limb has been dropped, cells at the site are activated and the tissues regenerate. This occurs in two stages:
- The cells work backwards – dedifferentiate – to become stem cells again;
- re-differentiate and multiply.
Tail regeneration in lizards has recently been extensively studied. Contrary to previous belief, the regenerated tail of a lizard is not a perfect replica of the orignial but a copy grown simply for aesthetic reasons.
The new tail of the green anole lizard, studied by ASU’s School of Life Sciences, consists of a single long tube of cartilage, with muscles spanning its whole length instead as opposed to the shorter fibres of the original.Pores in the regenerated cartilage allow blood vessels to pass through, but not nerves, which would normally pass through the gaps between the vertebrae of the original backbone. This suggests that the nerves grow from the tail stump into the regenerated part. “These differences suggest that the regenerated tail is less flexible, as neither the cartilage tube nor the long muscle fibers would be capable of the fine movements of the original tail, with its interlocking vertebrae and short muscle fibers,” said Rebecca Fisher, an associate professor in ASU’s School of Life Sciences.
To regrow an exact replica of the original tail, sections of vertebrae and spinal cord would have to be regenerated – a much more complicated process which would take up a lot more of the lizard’s time and resources. The simple regrown tail gives the lizard more balance than it would have with no tail at all, but is nowhere near as well engineered. As Fisher said, “The regrown tail is not simply a copy of the original, but instead is a replacement that restores some function.” (ASU News)