When choosing between life and limb, many animals are willing to sacrifice limbs. The ability to fall off the appendage is called self-amputation, or self-amputation. When backing into a corner, spider let go, claw drop crab and some small rodents shed patches of skin. Some Sea slugs will even cut off their own heads to rid their body of parasites.
But lizards may be the most famous for autobiography. To evade predators, many lizards cut off their still wiggling tails. This behavior confuses the predator, giving the rest of the lizard time to run away. While there are downsides to losing a tail – they’re good for locomotion, impressing a mate, and storing fat – it beats being eaten. Many lizards even have the ability to regenerate lost tails.
Scientists have studied this anti-predator behavior meticulously, but the structure that makes it work remains elusive. If a lizard can instantly lose its tail, what keeps it from getting into situations that aren’t life-threatening?
Yong-Ak Song, a biomechanical engineer at New York University Abu Dhabi, calls this the “paradox of the tail”: It must be simultaneously attached and able to separate. Dr Song said of the lizard: “It had to quickly detach its tail to survive. “But at the same time, it can’t lose its tail so easily.”
Recently, Dr. Song and his colleagues sought to solve the paradox by examining several newly amputated tails. They don’t want test subjects – according to Dr. Song, the NYU Abu Dhabi campus is crawling with geckos. Using small rings attached to fishing rods, they rounded up a number of lizards from three species: two types of geckos and a species of desert lizard known as the Schmidt fringed lizard.
Back in the lab, they pulled the lizards’ tails with their fingers, luring them into the act of dissection. They filmed the acquisition at 3,000 fps using a high-speed camera. (The lizards were quickly returned to where they were first found.) The scientists then glued the zigzag tails under an electron microscope.
On a microscopic scale, they were able to see that each fracture where the tail part separated from the body had mushroom-shaped pillars. Zooming in further, they saw each mushroom cap dotted with tiny pores. The team was surprised to discover that instead of sections of the tail knitting together along the fault plane, the dense microscopic pockets on each segment appear to only touch lightly. This makes the lizard’s tail appear like a brittle constellation of loosely joined segments.
However, computer modeling of tail-broken planes shows that mushroom-shaped microstructures are adept at releasing accumulated energy. One reason is that they are filled with microscopic voids, like the little holes and spaces between each mushroom cap. These voids absorb energy from a drag, keeping the tail intact.
Although these microstructures are able to withstand tensile forces, the team found that they are prone to shattering when slightly twisted. They determined that the tails were 17 times more likely to break when bent than when pulled. In the slow-motion video the researchers captured, the lizards twisted their tails to cleanly split them in half along a plane of fleshy fault.
Their findings, published Thursday in the journal Science, which illustrates how these tails strike the perfect balance between sturdiness and fragility. “It’s a great example of the Goldilocks principle being applied to a pattern in nature,” said Dr. Song.
According to Animangsu Ghatak, a chemical engineer at the Indian Institute of Technology Kanpur, the biomechanics of these lizards’ tails are reminiscent of sticky microstructures found on gecko’s sticky toes and tree frogs. “It has to be the right balance between grip and detachment, as that allows these animals to scale up to steep surfaces,” said Dr Ghatak, who was not involved in the study. Ghatak, who was not involved in the study. The feet of these animals are covered with billions of tiny hairs, which themselves consist of mushroom-shaped caps, he adds.
The researchers believe that understanding the process that allows lizards to clip their tails could have the potential to have prosthetic limbs, skin grafts or bandages, and could even help robots remove damaged parts.
However, Dr. Song is most delighted to finally understand how the creatures on campus escape predators.
“This project is purely driven by curiosity,” he said. “We simply wanted to know how the lizards around us cut their tails so quickly.”
https://www.nytimes.com/2022/02/17/science/lizard-tails-break.html The paradox of the lizard tail, solved