Severed gecko tails have a life of their own

By Richard Lam

The gecko, known for its ability to shed and re-grow its tail when threatened, may prove useful in researching traumatic human spinal cord injuries.

University of Calgary zoology professor Anthony Russell began studying leopard geckos during his sabbatical starting January 2009.

He worked with Tim Higham, a former U of C student of his, and now an associate professor at South Carolina. The original study concerned the energetics of tail re-growth.

“After a stress-induced detachment, we were interested in how the gecko proportions its energy to continue growing normally, while simultaneously regenerating its tail,” said Russell.

Testing with different diets, the goal was to find out what biological decisions were being made by the gecko during this process.

This eventually led to the study of the detached tails themselves. By measuring the electrodes and muscular outputs, combined with high-speed videography, the two made a surprising discovery.

“We were expecting the muscles to fire left and right in a predictable pattern, but something was released when the tail was shed; it behaved differently.”

Rather than the modest back-and-forth movement while still attached to the gecko, the tail began flipping and hopping at inconsistent intervals.

It was also found that this behaviour was unique to the leopard gecko. Russell explained that the gecko’s tail has evolved to react in this manner every time when facing a traumatic injury.

It is a useful defense mechanism to distract its predator long enough with its unexpected surges of kinetic energy to allow the gecko to escape. After a full minute of vigorous movement, the tail gradually slows down over half an hour, eventually running out of power.

This seemingly random activity — with no neurological input from the gecko’s brain — poses interesting questions.

What sensory input or stimulus, if any, is triggering the tail’s motor output? The detached tail now acts with an independent network of neurons known as a central pattern generator, explained Russell.

Until it is detached, these CPG signals appear to be suppressed by the brain’s higher neurological centre.

This leads to speculation of whether there is more than a one-way flow of information.

There is little research into the source or location of these CPGs, and Russell believes collaborating with neurologists can help illuminate injuries relating to the human spinal cord, which shares the same biological makeup as gecko tails.

The theory is that if a gecko doesn’t need a brain signal to move, perhaps a human won’t either.

There have been signs of involuntary movement in spinal cord injury victims, such as in the thenar pad below the thumb. These have been shown to be influenced by external stimuli such as changing temperature.

Additional studies are required to determine what influences the random movements of the detached gecko tails.

Russell is now hoping to learn if the skin receives sensory input, which may be feeding information back to the tail’s new CPG system to react in a certain way.

“By finding some way to isolate the various input stimuli, we hope to find out how much of these movements are biologically inherited, and how much is from environmental circumstances,” he said.