Few predators swallow their prey whole. Even fewer can digest their meals with bones and all. But for some reptiles like the Burmese python (Python bivittatus), calcium-rich skeletons aren’t a digestive concern—they’re a necessity.
Herpetologists have spent years trying to understand how bones are not only safe and healthy for the serpents, but how their biology manages to regulate when and how many bones to digest. Now, researchers believe they have identified an explanation hidden inside the “crypts” of specialized cells. Their findings are published this week in the Journal of Experimental Biology.
A team co-led by zoologist Jehan-Hervé Lignot at France’s University of Montpellier began peering inside Burmese python intestines using light and electron microscopy in an effort to better understand their dietary cycle of fasting and feeding. Lignot soon spotted tiny, unidentified objects along the snake’s intestinal lining, or epithelium.
“When I started analysing the ‘spheroids’ I initially thought it could be some bone fragments. But this rapidly proved to be wrong,” Lignot told Popular Science. “And, then, came the hypothesis that the particles could be produced by the intestine and by a specific cell type.”
A subsequent morphological analysis proved the theory correct: the spheroids were being produced from calcium, iron, and phosphorus within a newly identified type of cell. Specifically, the particles resided in what Lignot described as a “crypt” inside these narrow, specialized cells—but it wasn’t initially clear what these cells were programmed to do.
To find out, researchers studied the pythons’ intestinal cells after feeding them three different diets—a standard fare of whole rodents, a low-calcium variant of “boneless prey,” and a version that featured boneless rodents with higher-than-normal injections of calcium.
Pythons subsequently lacked the same calcium- and phosphorus-heavy particles when only fed boneless food. But when either snacking on regular bone-in rodents or a calcium-rich diet, snake cell crypts featured plenty of calcium, phosphorus, and iron spheroids. Additionally, those pythons’ droppings contained no bone fragments, showing that they had been dissolved entirely.
Lignot noted that while experts have previously located similar particles in insects and crustaceans, his team is the first to see something similar in vertebrates. Since then, he and his collaborators have also identified the bone-digesting cell in multiple other python and boa species, as well as the venomous Gila monster.
As for how many bones an average python in the wild can digest, Lignot isn’t quite sure—but he did offer a quick estimate.
“[It’s a] tough question… snakes can grab a prey that can be more than 30 percent of [its] body mass,” he said. “If we consider, as in humans, that our bones represent about 9-10 percent of our body weight, you can therefore have a significant amount of ions coming from the prey’s skeleton that is completely dissolved in the stomach.”
While Lignot has since moved on to other research areas, he hopes other investigators continue to search for the newly pinpointed cell type in other vertebrates.
“An evolutionary analysis would be awesome,” he said.
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