PROVIDENCE, R.I. [Brown University] — This won’t bring much comfort to a boa constrictor’s unlucky victims, but eating dinner puts the snake in a bit of a bind. The mechanics of squeezing a creature to death and then swallowing it whole create pressure on the boa’s ribs and lungs, restricting their ability to fill their lungs with oxygenated air.

Yet snakes have clearly overcome — some might even say mastered — the challenges of breathing while eating, and researchers have finally figured out how. A study published in Journal of Experimental Biology explains how boa constrictors are able to adjust which region of the ribcage they use to inhale, depending on whether they are resting, constricting or digesting.

“By showing how snakes were able to circumvent the mechanical constraints of constriction and large prey ingestion — the very things that helped distinguish them from other limbless elongate animals — this study provides a new perspective on snake evolution,” said John Capano, lead study author, who received his Ph.D. from Brown University in 2021 and is now a postdoctoral research associate in lab of Matt Fuxjager, a Brown associate professor in the Department of Ecology, Evolution and Organismal Biology.

Snakes don’t have diaphragms, so they rely entirely on the motions of their ribs to breathe, Capano said. To quantify individual rib motions, Capano and Elizabeth Brainerd, a Brown professor of biology and medical science, used a 3D imaging technology developed at Brown University called X-ray reconstruction of moving morphology (XROMM), which can show the rapid skeletal movement of live creatures. XROMM combines 3D models of bone morphology with movement data from x-ray video to create highly accurate re-animations of the bones moving in space (for example: birds flying, frogs jumping — and snakes breathing).

In the experiments, Capano and Brainerd secured a blood pressure cuff around the ribs of boa constrictors to restrict their movements. Capano attached tiny metal markers to two ribs in each reptile — one set of markers a third of the way down the snake’s body and another halfway along — to visualize how the ribs moved using X-rays. Then he positioned a blood pressure cuff over the ribs in both regions and gradually increased the pressure to prevent the ribs from moving.

Some of the snakes reacted to the feeling of the cuff by hissing defensively, thus filling their lungs with air and expanding their ribs “Hissing provided us with an opportunity to measure some of the biggest breaths snakes take,” Capano said.

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