Boa constrictors are known for their chokehold in attacking their prey. As these snakes coil around their prey, they squeeze the life out of their victim within minutes before swallowing it whole. But it remained a mystery how boa constrictors do not suffocate as they squeeze hard their prey and swallow as big as a monkey.
Now, researchers from Brown University observed via X-ray videos and other technology how the rib cage of these snakes are compressed when eating without affecting their breathing. As Science News reported, snakes would not have been able to swallow their prey whole without this ability.
A recovering boa constrictor feeds on a mouse at the Animal Hospital at the Niteroi Zoo, some 25 kms north of Rio de Janeiro, Brazil on August 5, 2009.
Snakes Use Their Rib Cage and Blood Pressure to Avoid Suffocation
Researchers led by biologist John Capano from Brown University attached metal markers on the ribs of three boa constrictors to track how these ribs move over different parts of the lungs of the snakes. Per NPR, boa constrictors have over 200 pairs of ribs running down the length of their bodies and breathe by rotating the muscles of their rib bones and pumping air in and out.
Snakes have lungs that are long and stretch down through their length. The part of their lungs nearest to their heads are rich in blood vessels because it is where gas exchange seems to take place, while the parts of the lung near the tail resemble an empty bag.
When a snake swallows its prey, its rib cage also expands wide open to accommodate the large animal. Researchers said that there is a chance that their ribs can not move during this time because they are at full capacity.
In their study, titled "Modular Lung Ventilation in Boa Constrictor, " published in the Journal of Experimental Biology, researchers described how they put blood pressure cuffs on different parts of the bodies of the snakes to prevent their ribs from moving. Capano said it was like putting a tiny helmet on the snake to measure the airflow and see how it was breathing.
The team monitored the nerve signals using X-ray videos that let them watch bone movement inside the snakes. Capano noted that the snakes would switch to breathing with a set of ribs back towards the tail when they put the blood pressure cuff on the front section of the snakes. When they take it off, the snakes would stop moving in the back and start breathing to the front.
The team suggests that the bag-like section of the snakes' lungs at its rear part operates like a bellows to air through the front part of the lungs, which is at the front side of the snake where gas exchange happens.
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The Trick Likely Contributed to the Success of Snake Evolution
Capano, the study's first author, said that the snakes' ability to control which section of their ribcage is involved in breathing probably allowed boa constrictors to successfully evolve into their present forms. "It doesn't seem like you could evolve constriction to kill really big things if you're compromising lung ventilation," Capano told Live Science.
Moreover, the trick also likely helps boas survive the process of swallowing and digesting large prey, given that its size could restrict the movements of their ribs. The authors reported that other snake species likely use the same trick in breathing while constricting and swallowing their prey.
They added that the method likely evolved with the highly mobile skulls of snakes so they could wrap their jaws around their enormous victims and swallow them in one gulp.
Unlike humans, snakes do not have diaphragms, so they use the muscles attached to their ribs to alter the volume of their ribcage and allow airflow. Researchers said that these muscles are integral to the snakes' ability to selectively engage ribs, and this likely developed very early in snake evolution.
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