A boa constrictor is feeding on a lizard in Tijuca Forest National Park.
Vitor Marigo / Aurora Photos/Getty Images/Aurora OpenSnakes that swallow huge prey have evolved a way to keep themselves from suffocating.
When the scaley coils closest to the snake are busy squeezing its dinner to death, the reptile can simply change how it breathes so that it uses ribs and muscles farther down the length of its body.
A new study shows that inflated blood pressure cuffs can be used to immobilize different parts of boa constrictors while simultaneously doing X-ray scans to monitor their ribs. Researchers observed that the snakes could easily shift to using different sets of ribs to draw in air.
The author of the study, John Capano, says it was remarkable that they had such fine control.
The boa constrictors have more than two hundred pairs of ribs running down the length of their bodies, and normally breathe by using muscles to rotate their rib bones and pump air in and out.
Like the rest of their bodies, the lungs of a snake are long. The part of the lungs closest to the head is rich in blood vessels, while the part of the lungs closer to the snake's tail is empty.
The front part of a snake's body is used to subduing a meal when it bites. The rib cage has to be spread wide open when a snake ingests a large animal.
When he was working in the lab of Scott Boback at Dickinson College, Capano and Boback noticed that when they fed snakes, it looked like they were breathing with another section of the body.
It was not clear if this was a change in breathing on the snakes. The physical demands of squeezing and swallowing prey kept some ribs from being able to move in order to breathe.
That was the beginning of the project, can they control it?
In the Journal of Experimental Biology, Capano and a team of researchers describe how they put blood pressure cuffs on different parts of snakes to prevent the ribs from moving. X-rays were used to watch bone movement inside the snake.
When they put the cuff on the front section of snakes, the animals would switch to breathing with a set of ribs back towards the tail.
The bag-like section of lung at the back of the snake appears to act like a bellows to draw air through the front of the snake, because the ribs at the far end of the snake only got involved when the front section was unable to move.
Jake Socha, a researcher who studies animal biomechanics at Virginia Tech University, says that the study shows that the snake has control over where it is ventilating.
Thousands of snake species thrive in environments from the ground to trees to the ocean. The long, limbless body has proven to be very adaptive, in part due to the fact that snakes have evolved ways of killing big animals.
The idea is that there had to be some respiratory innovations that went along with the evolution of constriction. There would have been pressure to move breathing to a different part of the ribcage.
She has been fascinated by how the mechanics for pumping air in and out of the lungs differ between animals.
While humans have an entirely different breathing setup from snakes, including a diaphragm and a breast bone that snakes don't have, Brainerd can't help but notice that people have a couple of more snake-like ribs.
Brainerd is interested in the extent to which we control the floating ribs separately.
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