How do boa constrictors avoid choking when they rush their prey?


Boa constrictors hunt by ambushing their prey and then squeezing captured animals to death with their muscle coils.

But like a boa tightens its body around a victim and cut off blood flow to this animal’s brainhow does the snake avoid squeezing all the air out of its own lungs and choking in the process?

It turns out that a boa constrictor can quickly adjust the section of its ribcage it uses to breathe, according to a study published March 24, 2022 in the Journal of Experimental Biology (JEB). So if a boa traps a squirrel or rat using the front half of its body, then the constrictor will use the ribs lower on its noodle-like body to keep breathing while it crushes the rodent. And similarly, the ribs closer to the animal’s head will take over if the dorsal ribs are currently pressed against an immobilized animal.

“Constriction is an incredibly energetically taxing behavior and almost certainly requires high oxygen demand,” said David Penning, assistant professor of biology at Missouri Southern State University, who was not involved in the study. The new research “helps clear up some of the confusion surrounding how oxygen delivery occurs during this harrowing process.”

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In addition to revealing how boas breathe during constriction, “I think this work can be used to make broader inferences beyond the boa constrictor,” Penning told Live Science in an email. “Not only do we know very little about how snakes work, but we also know little about the true metabolic demands of most of their activities.”

Snake Lung Evolution

This ability to control which part of their rib cage is involved in respiration likely allowed boas to evolve into their current forms, said study first author John Capano, a postdoctoral research associate in the Department of Ecology. , Evolution, and Organismal Biology from Brown University. “It doesn’t look like you can scale constriction to kill really big things if you compromise lung ventilation,” Capano said.

This precise breathing strategy likely also helps boas survive the process of ingesting and digesting large prey, as these large meals limit the movement of the interior animals’ ribs, Capano told Live Science. In their report, the study authors hypothesize that other species of snakes likely use this same breathing method, and that the method likely evolved in tandem with snakes’ highly mobile skulls, which contort to that animals can wrap their jaws around huge prey and swallow it. a sip, he added.

Unlike humans, snakes lack diaphragmsthe large domed muscles that contract and flatten to allow a person lungs to expand and fill with air, then relax and compress the lungs to expel the air. Instead, snakes use muscles attached to their ribs to change the volume of their rib cage and allow air to move in and out of the lungs.

When animals breathe with their ribcage, they typically use small muscles called intercostals that stretch between adjacent ribs, Capano said. These animals use intercostal muscles to move entire “blocks” of ribs at once, rather than having precise, independent control of individual ribs.

In comparison, boas and other snakes primarily use the levator muscles of the ribs for breathing; each levator costa extends from the vertebral column to one of the snake’s more than 400 ribs. In their new study, the team revealed how each levator costa “essentially can control movement much more discreetly,” Capano said. “He can just lift that individual rib.” When a levator costa contracts, it pulls the rib back, like a door on a hinge, while causing the bone to rotate slightly; these delicate movements control when and where the snakes’ lungs can inflate.

All snakes have fully developed right lungs, but depending on the species, a snake may have a puny left lung or no left lung at all, according to a 2015 report in the journal. PLOS One. Boa constrictors belong to the first group, in that they have a very small left lung and a long right lung that is about one-third the length of the snake’s body, the JEB report notes.

The front third of the long lung, closest to the snake’s head, contains tissue capable of gas exchange, meaning it can pass oxygen into the blood and remove or exhale waste products, such as carbon dioxide. The back two-thirds of the lung cannot perform gas exchange and is essentially “just a sac,” Capano said.

This image highlights the different regions of the ribs that a boa constrictor uses for breathing while resting, constricting prey, and digesting a meal. (Image credit: Scott Boback)

Scientists have different theories as to the function of this sac-like region, but the new study supports the idea that it acts as a kind of bellows that helps draw air through the front part of the lung which exchanges throttles, Capano said. So when the front of the lung cannot fully expand – when the boa is busy mastering a snack – the back of the lung can still suck air through the tissues and allow gas exchange.

“Even if your forehead [lung] can’t move, or even if something crushes it, you can still suck air through it,” Capano said. “And then in doing so, you’re still sucking oxygenated air through your vascular tissue .”

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The team found that boa constrictors use this unique breathing method by placing blood pressure cuffs on adult boas in their lab to restrict the movement of certain snake ribs. The team used a variety of techniques to measure the airflow in and out of the snakes’ lungs and the electrical activity of different muscles. They also used a technique called “X-ray reconstruction of morphology in motion” (XROMM) to track the movement of the snakes’ ribs, in real time.

Using XROMM involved placing small metal markers on a few of the snakes’ ribs, then scanning the animals from the side and above as they moved. By combining images taken from both viewpoints, the team captured how the ribs moved in three dimensions and created detailed models of the moving rib cage, Capano said.

The new study shows how the boas’ rib movement changes in response to the blood pressure cuff, which presses the animal from all sides, Penning said. That said, when a snake actually constricts an animal, the side of the snake that makes contact with the prey “probably does most of the work by exerting force”, while the other side of the snake may be compressed less, in comparison, he noted.

So there may be slight differences in how snakes adjust their breathing to accommodate cuff pressure, compared to how they choke their prey; Penning said he would be interested in seeing these differences studied in the future. For the future, Capano said he wants to study how boas and other snakes move their ribs during different dynamic behaviors, such as gliding.

Originally posted on Live Science.


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