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Lizards are well known for snapping off their tails when a predator snags them from behind, but that defense strategy doesn’t mean it's game over for the disembodied tail. The abandoned appendage has a network of neurons that guides it to flail about even after losing its connection to the brain.
Biologists at Clemson University and the University of Calgary noticed that the movements of the luckless tails of leopard geckos seemed more complicated than those of other lizard tails. So the scientists tracked the gecko tails post-snap and found that they jump, flip and lunge, presumably to distract predators and give the gecko time to make its getaway.
"No one had ever documented anything other than simple swinging, sort of like a pendulum,” says Timothy Higham, an assistant professor in the Department of Biological Sciences at Clemson. Higham and Anthony Russell at the University of Calgary published their results last week in Biology Letters.
To arrive at the findings, four leopard geckos first were anesthetized so four small electrodes could be inserted in their tails. Once the lizards recovered from the anesthetic, their tails were pinched at the base to trigger the animals to "autotomize," or cast off, their tails. Then, the researchers created a timeline of the movements of each tail using the electrode data on muscle activity as well as images captured by a high-speed video camera.
The four tails exhibited similar movements that lasted about 30 minutes and did not seem to depend on cues from the environment. By looking at different sections of the tails, the team will now "try to get to the neurobiology of it, and try to figure out where the signals are coming from," Higham says.
This strange finding could help illuminate why people with spinal cord injuries experience spontaneous muscle contraction, and also could provide insights into how to help these patients restore normal movement.
One idea for how the signals work, Higham explains, is that, after severing a lizard's tail or injuring a spinal cord, neurons in these areas lose connections to other neurons that inhibit motion. Identifying the inhibitory signals could help doctors treat the twitching that typically occurs after spinal cord injury.
The current approach to studying spontaneous spinal movement involves cutting the link between the spine and brain in cats or fishes. Besides being difficult systems, the spines of these decerebrated animals only show the simple swinging motion that researchers have seen for other species of lizards.
Higham thinks that the tails of leopard geckos have adapted an advanced movement repertoire to distract predators because "this species lives in the desert so it might benefit to have complex motion…out in the open," he says.
Photograph of leopard gecko: ©iStockphoto/ Branislav Senic