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Gecko's tail an energy powerhouse

It may help them escape, but when geckos drop their tail to flee a predator it appears they are also dumping the fuel that gives them energy to run away.

The finding by an international team is published in this week's Physiological and Biochemical Zoology.

Co-author Dr Trish Fleming, of the School of Veterinary and Biomedical Sciences atMurdoch University, says caudal autotomy, or the ability to shed the tail in response to attack, is a major predator escape mechanism in species within 13 of the 20 lizard families.

The loss of the tail allows the lizard to break away from a predator that has seized it by the tail.

The tail may then also act as a distraction through spontaneous writhing or wriggling movements, engaging the predator's attention while the lizard flees, Fleming says.

Ahead of the study, Fleming and her colleagues predicted South Africa's Cape dwarf gecko Lygodactylus capensis would become faster after loss of its tail as a result of reduced friction with the ground or reduced body mass.

However, "contrary to our expectations, tailless geckos overall expended less effort in escape running, moving both slower and for a shorter distance, compared with when they were intact", she says.

Fleming says she suspects the results will translate across lizard species.

Speed measured

For the study the tiny geckos, which are just a few centimetres long and weigh less than one gram on average, were made to run along a one metre glass tube with a wax floor while their carbon dioxide production, speed and distance travelled were measured.

Each gecko was trialled with its tail intact. The researchers then induced the lizards to lose their tail by holding it with a pair of tweezers.

Two days later the geckos were put through the running trial again.

Fleming says initially the tailless geckos were slightly faster, but not by a statistically significant amount.

However over a distance of about 10 metres the tailless geckos were both slower and the distance covered was reduced, although the time they ran for remained the same.

"We found a 19% reduction in the distance ran for our tailless geckos compared with when intact," says Fleming.

She believes the results show the geckos use the fat stored in their tails, which make up about 8.7% of body mass, as "fuel for running".

Energy loss

Fleming says without the tails the geckos may have less fatty acids in the bloodstream to sustain locomotion.

She says reduced stamina suggests that lack of energy reserves stored in the tail (eg fat) may play a signiﬁcant role in the locomotory energetics of these animals.

However Fleming believes more work needs to be done on understanding the biochemistry of the gecko to support this hypothesis.

A follow-up study, which is yet to be published, shows the geckos' behaviour also changes post tail loss.

She says field trials looked at how quickly tailless geckos would run away from a perceived predator and how long it would take them to re-emerge.

The tailless geckos were much more wary, says Fleming.

"They recognise their altered state and vulnerability and are altering how they behave."