This Western Fence Lizard started life with the long and intricately patterned tail that’s natural in the species, see photo below. Then something happened. Either a natural predator — maybe a Barn Owl or another raptor — or a human seized the lizard by the tail, and the lizard cut it loose. The lizard is a member of the 13 families of lizards capable of dropping its tail when attacked. The process is termed caudal autotomy, or self-amputation of the tail. In most of these lizard species, the tail vertebrae have a fracture plane which the animal can break by tightening a sphincter muscle. A skin flap closes over the wound and prevents hemorrhage from the artery and impedes invasion by parasites and bacteria. After being jettisoned, the tail goes on twisting and curling for a few minutes, capturing the attacker’s attention and diverting it while the lizard minus tail scoots to safety. And then the lizard regrows the tail. Only, the second growth isn’t a perfect copy of the original. It’s not as long, it’s not bony, and it lacks the detailed scales and coloring. It’s like a stub, a job unfinished. That’s the best the lizard can do. That’s a lot better than a mouse can do, or a human. Mammals can’t regrow limbs at all, although two species of African spiny mice, when attacked, are able to release and then perfectly regrow patches of skin. But the lizard’s repair work is not as good as the salamander’s. Some salamanders can regrow not only perfect tails, but also brain and heart tissue, parts of their eyes, and limbs. Scientists probing these issues have pointed to differences in the stem cells in the spinal cord; see this summary and the original research article. The long-term objective of the research is to figure out a way that mammals can copy the regenerative abilities of salamanders, or at least the imperfect tail-work of lizards. That’s still a long way off.
Dropping the tail saves the lizard’s life, but there’s a cost. It takes energy to regrow the tail, and the new tail is not as good for quick mobility or for storage of fat as the old one. Stub-tailed lizards are not as attractive as mates, and in some species, loss of the tail exposes the lizard to heavier infestation of parasites. Can the lizard drop its tail a second time? Apparently yes, but only upstream from the new tail, because the new tail consists of ligament and does not have the bony vertebrae with their built-in fracture planes.
Thanks to Peter Rauch for the key to this tail tale.
The Western Fence Lizard is scientifically interesting in another way as well: it conveys immunity to Lyme disease. Read this earlier post to learn more.