Thursday, January 19, 2012

LIFE - Zoologger: Gecko's amputated tail has life of its own

Don't follow that tail <i>(Image: Apostrophe Productions/Getty)</i>
Don't follow that tail (Image: Apostrophe Productions/Getty)

"It's just a flesh wound," claims the Black Knight after having both arms chopped off by King Arthur Рat least, that's how Monty Python imagined it. "I've had worse." Most of us are less blas̩ about loss of limb: in particular, we are reluctant to cut off our own appendages unless the situation really, really demands it.
In the animal kingdom, amputation is common: many city-dwellers are familiar with the sight of one-legged pigeons. Most cases are accidental, but some animals deliberately shed an appendage in order to distract predators.
The common leopard gecko does just that, shedding its tail when under attack. Rather unexpectedly, though, that's not the end of the tail. It keeps moving for half an hour, and may even be able to respond to events around it.

Off with his tail!

Shedding appendages to escape predators may sound extreme, but autotomy, as it's known, is actually rather common. Many lizards and snakes do it, as do octopuses, spiders and even a few mammals: threatened Cuvier's spiny rats sometimes shed their tails. Sea cucumbers are the true champions, though: when predators attack they literally spill their guts.
When a limb or organ gets separated from the body it normally stops working pretty quickly. People who have their heads chopped off, for instance, retain consciousness for seconds at most.
Not so the tails of leopard geckos: they can stay active for 30 minutes after their owners have abandoned them. Timothy Higham of the University of California, Riverside, and Anthony Russell of the University of Calgary in Alberta, Canada, showed in 2009 that the geckos' detached tails can pull off two different manoeuvres.
They rhythmically swing from side to side, and for the first few minutes after amputation they also flip and jump up to 3 centimetres into the air.


To find out how the tail keeps moving, Higham and Russell implanted four electrodes into the tails of four sedated leopard geckos. Then they woke the lizards up and pinched the bases of their tails, inducing the geckos to shed them. The researchers then recorded the electrical activity from the tails as long as they kept moving.
The two types of movement followed different patterns of electrical activity. The tail jumped or flipped when both sides were activated simultaneously, whereas – not surprisingly – it swung from side to side when first one side then the other was activated.
Jumps and flips were triggered by bursts of pulses that varied much more in length than those triggering rhythmic swinging. Higham says this suggests they are controlled by separate neural circuits, rather than a single circuit that can send out different signals.
The swinging seems to be controlled by an automatic process, but the jumps and flips are far more erratic. Higham says the circuit controlling them may be linked to the tail's touch receptors, so the jumps and flips could be a response to external stimuli.
Having a tail that remains responsive after being detached may seem pointless, but it could be a lifesaver. If the tail starts jumping when a predator tries to bite it, it may lure the hunter to chase after it. While this wild tail chase is going on, the gecko itself can make good its escape.
Fortunately, the Black Knight's limbs were not up to leopard gecko standards, or King Arthur might never have made it to confront the fearsome Rabbit of Caerbannog.

Journal reference: The Journal of Experimental Biology, DOI: 10.1242/jeb.054460

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