News in Science

Gecko tails dance to their own tune

Geckos are known to discard their tail to distract a predator, but researchers have discovered what happens to the appendage after its owner flees.

Professor Anthony Russell of the University of Calgary in Canada says the new finding could shed light on the functions of the spinal cord and the effects of spinal cord injury.

According to the study, in the journal Biology Letters, the detached member continues to leap, lurch and lunge, sometimes in intricate patterns never before detected, for up to 30 minutes.

The remarkable ability of geckos to drop tail and run has been the object of scientific scrutiny for over a century.

Earlier experiments have shown that 'lizard tail autonomy' provides a visual decoy that entices an attacker to pounce on the tail rather than the gecko.

In addition, travelling light allows the lizard to run even faster, boosting its chances of escape and survival.

On the down side, a tail-less gecko is at a distinct disadvantage when it comes to jumping and climbing. It may also find itself scrambling to find a suitable mate.

Russell, along with Assistant Professor Timothy Higham of Clemson University in South Carolina, wanted to take things a step further by analysing exactly how the severed tails move.

Complex movement

Using electromyography (EMG) and high-speed video, they monitored tails from the instant of separation from four specimens of Eublepharis macularius, also known as the leopard gecko.

EMG detects the electric potential generated by muscle cells, both when they are active and at rest, and is frequently used to analyse the biomechanics of movement.

Unlike most animals or animal parts moving without the active control of a brain, the gecko tails didn't simply jerk about in a regular pattern.

"We discovered that the tail has an intricate repertoire of varied and highly complex movements, including acrobatic flips up to three centimetres in height," says Russell.

From an evolutionary vantage point, rhythmic movements interlaced with sudden jumps and flips enhance unpredictability, further distracting the predator, the researchers write.

Natural selection may also have favoured sustained and complex movement so that the tail can escape too: geckos have been known to return to the scene of their dismemberment to eat their own tail, presumably to compensate for the loss of the precious fats stored there.

Sensory feedback

More research is needed to understand exactly how a bundle of nerves detached from a brain can perform such complex behaviours, the researchers says.

"The most plausible explanation is that the tail relies on sensory feedback from the environment. Sensors on its surface may tell it to jump, pivot or travel in a certain direction," says Russell.

While many of the movements seemed to be self-initiated, the tails almost always lunged in a certain way when they touched the edge of the enclosure in which the experiments took place.

The study shows that the signal triggering movement starting at the far tip of the tail, the likely location of a control centre activated only after detachment from the rest of the body, and the brain, has occurred.