Pythons are notorious for their eating habits. After suffocating their prey with their lithe bodies, these large snakes swallow the animal whole. Now, researchers have shed new light on the cellular mechanisms that allow them to digest entire skeletons.
The study, presented July 9 at the Society for Experimental Biology Annual Conference in Belgium and published in the Journal of Experimental Biology, investigated the intestinal cells of Burmese pythons. Adult males can grow to be 10 to 16 feet (3 to 5 meters) long, and their impressive size allows them to feed on a wide variety of mammals and birds, including deer and alligators. Unlike other carnivores that only eat flesh, snakes rely on animal skeletons as a calcium source. Absorbing all the available calcium from a skeleton, however, could result in too much of this nutrient entering the serpent’s bloodstream. Called hypercalcemia, it can lead to heart conditions, high blood pressure, bone defects, and kidney failure in reptiles.
“We wanted to identify how [pythons] were able to process and limit this huge absorption of calcium through the intestinal wall,” said Jehan-Hervé Lignot, lead author and a professor at the University of Montpellier, in a statement.
To that end, Lignot and his colleagues fed pythons one of three different diets: normal rats, boneless rats, or boneless rats enriched with calcium carbonate to match natural bone calcium levels. One group of snakes did not receive any of these diets and instead fasted for three weeks to provide a baseline. Three to six days post-feeding, the researchers humanely euthanized and dissected the snakes to extract their small intestines.
They then analyzed the enterocytes, or intestinal lining cells, of the pythons using light and electron microscopes alongside measurements of blood calcium and hormone levels. This revealed a never-before-seen type of cell that produces large particles made from calcium, phosphorus, and iron. These particles form structures that Lignot calls “spheroids.”
“A morphological analysis of the python epithelium revealed specific particles that I’d never seen in other vertebrates,” Lignot said. He and his colleagues found these particles inside the internal “crypt”—a small pocket or cavity—of specialized cells that differed from traditional intestinal cells. “Unlike normal absorbing enterocytes, these cells are very narrow, have short microvilli [finger-like membrane protrusions], and have an apical fold that forms a crypt,” he added.
The three different diets that the pythons ate allowed the researchers to assess the function of these unique cells. In snakes that ate boneless prey, the enterocytes did not produce the calcium and phosphorous-rich particles. In those that ate either whole rodents or calcium-supplemented boneless rodents, however, the cells’ crypts filled with large particles of calcium, phosphorus, and iron. This suggests that these cells play an important role in breaking down the bones of a python’s prey. The researchers found no bones in the snakes’ feces, confirming that all skeletons were completely digested and dissolved inside their bodies.
Though it was first identified in Burmese pythons, this new cell type isn’t unique to them. Since that initial discovery, the researchers have found these specialized bone-digesting cells in other species of pythons, boas, and the Gila monster, a species of venomous lizard native to the southwestern U.S. and Mexico.
The findings seem to point to an understudied system of mineral regulation in the digestive tracts of reptiles. However, it is possible that this mechanism extends to other types of bone-eating carnivores too, such as sharks and other marine predators, aquatic mammals, or raptors like the bearded vulture, according to Lignot. He told Gizmodo he hopes this work will inspire other researchers to search for these newly discovered cells across the animal kingdom.
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