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When it comes to gliding, most snakes do it the same way: straight ahead. But for snakes that live in deserts, getting around can be a challenge.
“As we know when trying to move on sand on a beach or elsewhere, it can be difficult to move around these materials that give way under your feet as you go,” said Jennifer Rieser, professor of physics at Emory University in Atlanta.
This is why the sidewinders slide to the side. Although some snakes can move sideways under certain conditions, Dr Rieser said, sidewinders – the common name for a group of three distant vipers found in the deserts of Africa, the Middle East and North America. – have raised this unique form of movement. to an art. The crosswind rattlesnake, for example, can travel at a speed of 18 miles per hour, making it the fastest snake in the world.
Now, a new study by Dr Rieser and his colleagues may have found their secret: scales filled with tiny pits, instead of the tiny spikes found on the bottom of other snakes. Their research was published Monday in Proceedings of the National Academy of Sciences.
The microstructure of snake bellies is important to the way they move, Dr Rieser said, because this is how limbless animals interact with the ground. To examine the microstructure of the Sidewinder scales, his team used an atomic force microscope to scan naturally lost snakeskin, provided by institutions such as the Atlanta Zoo. They then built mathematical models to test how the structures they saw would perform under different types of friction.
Although they appear smooth to the naked eye, the belly scales of most snakes have microscopic tips oriented from head to tail. These create friction between the snake’s body and the ground, Dr Rieser said, which helps them move forward in a familiar slither head-first.
Snakes from a wide variety of habitats and ecological roles – including close relatives of the sidewinder rattlesnake, such as cottons or diamond-backed rattlesnakes – have these prominent spikes on their bellies.
But the lateral species have reduced or eliminated these spikes, exchanging them for abdominal scales which are covered with microscopic pits that can move in any direction. Dr Rieser suggests this is because directional friction makes movement in a frictionless environment more difficult: “Imagine a snake trying to move over linoleum or silk.”
Rather, sidewinding depends on lifting large pieces of the body into the air as the animal moves. Scales that create strong directional friction perform very poorly with this type of movement, according to Dr. Rieser. But if the friction of the ladder is uniform in all directions, it greatly facilitates the crosswind.
The Sahara horned viper and the Namib Desert side adder – which are closely related – have abdominal scales with uniform pits and no spikes. But the crosswind rattlesnake, which comes from a different branch of the viper family tree, still has some vestigial belly spikes as well as pits.
One possible explanation for the difference is that the deserts of southwestern North America are only 15,000 to 20,000 years old, compared to the deserts of North Africa, which are between 7 and 10 million years old. .
“So maybe there was less time for the American sidewinders to evolve the structures that could help this type of movement,” Dr. Rieser said.
While the team’s hypothesis on the precise function of microscopic pits will require further study, the loss or reduction of these abdominal spikes in distant sidewinders suggests that these changes are a direct adaptation to lateral movements, they suggest.
“Given that movement is so crucial for survival, it’s reasonable to think that’s part of the reason this shift has happened,” said Dr Rieser.
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