Severed Gecko Tails Have a Mind of Their Own

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Even after they’re no longer connected to a lizard brain, gecko tails can flip, jump and lunge in response to their environment — and may even be able to evade predators.

Researchers have known for centuries that some animals can voluntarily shed parts of their bodies to keep from being eaten, but few studies have looked at the behavior of disposable body parts once they’ve fallen off. Now, using high-speed video and a technique called electromyography, scientists have discovered that severed gecko tails exhibit complex behavior and even seem to react to environmental cues.

“We expected a series of rhythmic movements that would slow down over time,” said biologist Anthony Russell of the University of Calgary, who co-authored the paper published Wednesday in Biology Letters. “What we found, however, was that the tail would flip left-right-left-right for awhile, and then do a jump, pivot around, and do another flip.”

The scientists say that figuring out what controls the jumping gecko tail may help us understand why the paralyzed muscles of spinal cord injured patients sometimes exhibit spontaneous muscle contractions, which they hope could someday lead to treatments that restore some control over such movements.

After attaching electrodes to the tails of four adult leopard geckos, the researchers gently pinched the lizards to encourage them to shed their tails. As soon as a gecko felt threatened, its tail began to twitch and eventually detached from the rest of its body in an amazing, but nearly bloodless, feat.

The researchers immediately placed the severed tails into a recording arena, as shown in the video below.

http://www.wired.com/wiredscience/2009/09/geckotail/



Rather than using up all their energy in a single short burst, the gecko tails seemed to modulate their muscle movement to conserve energy and maximize the unpredictability of their behavior. The tails also changed direction and speed depending on what they bumped into, which suggests that the tails can independently sense and respond to their environment.

“The tail is buying the animal that shed it some time to get away,” Russell said. If the tail simply moved rhythmically back and forth, predators would quickly recognize a pattern and realize they’d been duped. Unpredictable tail movements keep predators occupied longer, and in some cases, they may even allow the tail itself to escape.

“Leopard geckos store fat in their tail, and a lot of their resources are tied up in there,” Russell said. “The tail may move far enough away that it actually evades the predator, so that the owner can come back and eat its own tail to recoup some of the resources.”

Although the researchers understand the benefits of a detachable tail with a mind of its own, they don’t yet know what’s controlling the tail’s complex movement. According to Russell, figuring out what controls severed gecko tails might help us understand and treat some aspects of human spinal cord injury. “With a spinal cord injury, what tends to happen is skeletal muscles tend to be paralyzed behind that event,” he said. “For instance, if you injure your mid back, your lower limbs are put out of commission.”

But for several days to weeks after a spinal cord injury, paralyzed muscles often exhibit spontaneous, uncontrolled bursts of activity. “People really don’t understand how that happens,” Russell said, “what’s actually bringing about these spontaneous contractions without any major central nervous system control.”

Scientists know that networks of neurons called central pattern generators, or CPGs, can produce rhythmic movements that aren’t controlled by the brain, but they don’t know exactly how these neural networks function. To study CPGs, scientists usually have to surgically damage an animal’s spinal cord in a procedure called a “spinal preparation”; geckos provide a unique model system because they naturally sever their own spinal cords.

“This is a system that has evolved to be a spinal preparation that’s out there in nature,” Russell said, “doing something valuable for the animal.”

This is awesome! Thanks for sharing this!
My leo dropped her tail before I got her (a rescue) and that was really interesting. I've seen videos on youtube of leos dropping their tails, but this was really interesting!

Very interesting!