While snakes are famous for the venom they can inject with every bite, this is not the case with all species. Some actually use a more “crafty” method to overcome their prey. For example, so-called constriction snakes use their muscular bodies to pull their victims together until they interrupt their circulation or suffocate them.
Among them is the reticulated python, the great anaconda or the famous boa constrictor. But how do these reptiles not suffocate themselves by killing their prey? By enclosing the latter, they could very well also block their own breathing. This is the mystery that researchers wanted to reveal through a new study.
And they came up with a fascinating discovery. According to their work published in late March in the journal Journal of Experimental Biology, the boa constrictor is able to modulate the segments of its chest that it uses to breathe. A method he also uses to rest or digest his most hearty meals in peace.
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Muscles to move the ribs
The boa constrictor has two lungs, but only one, the right one, is fully developed and functional. Moreover, like other snakes, it does not have a diaphragm, this muscle that plays a crucial role in the ventilation of mammals – including humans – by allowing the expansion and contraction of the chest.
To breathe, reptiles must use other muscles attached to each of their ribs to vary the volume of their chest. “In the absence of a diaphragm, they must rely entirely on the movements of their ribs“, confirmed in a press release, John Capano, researcher at Brown University and first author of the study.
Researchers already suspected that boas were able to finely modulate this arrangement to allow their lungs to continue to breathe. Still needed to be confirmed. To do this, Capano and his team placed metal markers on two ribs of adult specimens to visualize how the bones moved using X-ray scanners.
They then placed a blood pressure cuff at both rib areas and used it to increase the pressure gradually. “Either the animals were undisturbed by the armband, or they became aggressive and hissed in an attempt to lure the researcher away.“, said the specialist.
Whistling allows reptiles to fill their lungs, “it was an opportunity to measure some of the greatest breaths taken by snakes“, he continued. The data set made it possible in three dimensions to observe the movements of the ribs and the chest and to recreate detailed models of them.
Independently controlled portions of ribs
The observations confirmed the suspicions: they showed that the Boas are able to control the movements of the ribs in the different parts of their cage independently. Thus, when the subjects were compressed at the level of the first third of their body, they breathed using the ribs located lower down.
Conversely, when the compression took place lower, the snakes breathed using the ribs located closer to their head. The strategy is all the more remarkable as not all parts of their lung are alike: the first upper third contains tissues capable of performing gas exchange, particularly to direct oxygen into the bloodstream.
On the other hand, this is not the case with the lower ones, which act more like a simple balloon by storing air. Thus, the researchers observed that when the upper part is compressed, the lower part of the lung can always take over by storing the air and then leading it back to the upper zone to allow breathing.
“Even if your upper lung is unable to move, or even if something is compressing it, you can still get air through it. And by doing this, you continue to send oxygenated air through your vascular tissue.“, John Capano confirmed LiveScience. The boa would thus modulate the movements of its ribs as desired according to the compression exerted.
An important strategy for the survival of the snake
However, the narrowing is only the starting point for the meal. The predator must then swallow it up and digest it. Two other activities that without such an adjustment could also compromise his breathing. “It would have been difficult for snakes to develop this behavior without the ability to breathe.“, Supported the co-author of the study.
This research sheds new light on the biology of the boa constrictor, which despite its reputation and success as a pet remains relatively unknown. Until recently, for example, it was believed that the constriction exerted by the snake killed the prey by suffocation.
However, research published in 2015 showed that it instead caused a stop in the blood circulation and lack of oxygenation of the organs. Earlier in 2012, a study conducted by the same team also found that the reptile could monitor its victim’s heart rate so it knew when to stop compressing.
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