The Lizard Tail Paradox, Solved

When choosing between life and limb, many animals voluntarily sacrifice the limb. The ability to drop the appendages is known as autoto...


When choosing between life and limb, many animals voluntarily sacrifice the limb. The ability to drop the appendages is known as autotomy or autoamputation. When cornered, the spiders let go of their legs, the crabs drop their claws and some small rodents shed tufts of skin. Some sea ​​slugs will even decapitate themselves get rid of their parasite-infested bodies.

But lizards are perhaps the best-known users of autotomy. To escape predators, many lizards drop their still-wagging tails. This behavior confuses the predator, giving the lizard time to flee. While there are downsides to losing a tail – they’re handy for maneuvering, impressing friends, and storing fat – it’s better to be eaten. Many lizards are even able to regenerate lost tails.

Scientists have studied this anti-predatory behavior meticulously, but the structures that make it work remain puzzling. If a lizard can lose its tail in an instant, what keeps it attached in non-life threatening situations?

Yong-Ak Song, a biomechanical engineer at New York University Abu Dhabi, calls this the “tail paradox”: it must be both grippy and detachable. “It has to detach its tail quickly to survive,” Dr Song said of the lizard. “But at the same time, he can’t lose his tail too easily.”

Recently, Dr. Song and his colleagues sought to resolve the paradox by examining several freshly amputated tails. They didn’t want test subjects – according to Dr. Song, the NYU Abu Dhabi campus is crawling with geckos. Using tiny loops attached to fishing rods, they collected several lizards of three species: two types of geckos and a desert lizard known as Schmidt’s Fringe Lizard.

Back in the lab, they pulled the lizards’ tails with their fingers, prompting them to perform acts of autotomy. They filmed the resulting process at 3,000 frames per second using a high-speed camera. (The lizards were quickly taken back to where they were first found.) Then the scientists glued the wriggling tails together under an electron microscope.

On a microscopic scale, they could see that each fracture where the tail had detached from the body was full of mushroom-shaped pillars. Zooming in even further, they saw that each mushroom cap was dotted with tiny pores. The team was surprised to find that instead of parts of the tail fitting together along the fracture planes, the dense pockets of micropillars on each segment appeared to touch only lightly. This made the lizard’s tail look like a snapping constellation of loosely connected segments.

However, computer modeling of the tail fracture planes revealed that the mushroom-shaped microstructures were adept at releasing stored energy. One reason is that they are filled with tiny gaps, like tiny pores and spaces between each mushroom cap. These voids absorb the energy of a tug, keeping the tail intact.

Although these microstructures can withstand pulling, the team found that they were susceptible to breaking if slightly twisted. They determined that tails were 17 times more likely to fracture when bending than when pulling them. In the slow-motion videos taken by the researchers, the lizards twisted their tails to cut them cleanly in half along the fleshy fracture plane.

their findings, published Thursday in the journal Science, illustrate how these tails strike the perfect balance between firm and fragile. “It’s a great example of the Goldilocks principle applied to a model in nature,” said Dr Song.

According to Animangsu Ghatak, a chemical engineer at the Indian Institute of Technology, Kanpur, the biomechanics of the tails of these lizards are reminiscent of the sticky microstructures found on the sticky toes of geckos and tree frogs. “It has to be just the right balance of grip and detachment because it allows these animals to scale steep surfaces,” said Dr Ghatak, who was not involved in the study. He added that the animals’ legs were covered in billions of tiny hairs that were themselves made up of mushroom-shaped caps.

The researchers believe that understanding the process that allows lizards to shed their tails could be useful for attaching prosthetics, skin grafts or bandages, and could even help robots get rid of broken parts.

However, Dr. Song is very happy to finally understand how the creatures on campus escape predators.

“This project was completely driven by curiosity,” he said. “We just wanted to know how the lizards around us cut off their tails so quickly.”

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Newsrust - US Top News: The Lizard Tail Paradox, Solved
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