The tail of the Tokay gecko instantly breaks off during a predator attack with the help of pre‑formed lines of weakness.

Geckos are small lizards that can escape an attacking predator using an unusual strategy—by instantly losing their tails. This process of actively shedding a whole body part is called autotomy. When a predator grasps onto a gecko, releasing the tail can help the gecko wriggle free and escape while the attacker is holding onto a severed tail or distracted by it.

In the Tokay gecko (Gekko gecko), structures in the tail appear to help the shedding process. First, the base of the tail has built-in lines of weakness going across it, similar to perforated lines or score lines that make pieces of paper easier to tear apart. These lines of weakness, or fracture planes, cross the tail’s skin, muscles, bones, and other tissues. Like many animals, the gecko’s muscles form segments spanning the length of the body and tail. Sheets of connective tissue separate neighboring segments. The fracture planes run through the connective tissue between muscle segments and continue through the bony vertebrae that make up the backbone in the tail.

When not under threat, the gecko’s tail is likely held in place by adhesion between the two sides of a fracture plane. This adhesion may be enhanced by the shape and arrangement of the muscle segments. Each segment can be thought of as a sideways “W” that interlocks with neighboring W-shaped segments. Compared to simple flat surfaces, the W-shaped structures have more surface area for adhesion. Micro-sized structures on the tips of individual muscle fibers also appear to play a role in tail adhesion and release. Researchers hypothesize that the shape of muscle fiber tips at the fracture plane can change to reduce adhesion during autotomy, making the tail easier to release. Contracting muscles around the fracture plane are also likely to help break tissues and release the gecko’s tail. Adhesion in this system appears to be a balance between enabling easy tail release when it’s needed, but preventing accidental release when it’s not.

Autotomy occurs in many other animals, including other lizards, as well as amphibians and sea stars. Many of these animals can also regenerate their lost body parts over time.

Image: Sanggaard et al. 2012 / CC BY - Creative Commons Attribution alone

A) Blue stain: connective tissues and scales; red stain: muscles; white: adipose tissues. B) Close up of the fracture plane in the skin. C) Electron microscope image showing cells that might be part of a “cellular zipper” in the fracture plane. © 2012 Sanggaard et al. Unique Structural Features Facilitate Lizard Tail Autotomy. PLoS ONE 7(12): e51803. http://dx.doi.org/10.1371/journal.pone.0051803

Image: Sanggaard et al. 2012 / CC BY - Creative Commons Attribution alone

Scanning electronic microscope image of the W-shaped muscles extending from the gecko tail stump. The tips of individual muscle fibers are visible on most sides of the muscle. © 2012 Sanggaard et al. Unique Structural Features Facilitate Lizard Tail Autotomy. PLoS ONE 7(12): e51803. http://dx.doi.org/10.1371/journal.pone.0051803

Image: Sanggaard et al. 2012 / CC BY - Creative Commons Attribution alone

A and B) Parts of the W-shaped muscles extend from the tail stump. C) The exposed end of the gecko where the tail once attached shows pockets where extensions from the W-shaped muscles fit. © 2012 Sanggaard et al. Unique Structural Features Facilitate Lizard Tail Autotomy. PLoS ONE 7(12): e51803. http://dx.doi.org/10.1371/journal.pone.0051803

Image: Richard Ling / CC BY SA - Creative Commons Attribution + ShareAlike
Last Updated April 20, 2018