During the 1990s the Burmese Python (Python bivittatus) hit the headlines because of research done by Stephen Secor and Jared Diamond in Los Angeles. Secor was a postdoc in Diamond’s lab. Jared Diamond is of course the polymath who had three simultaneous careers: as a physiologist (in which capacity we have twice given invited papers at the same conference*); as an ornithologist and ecologist working in New Guinea; and as a student of the history of the human environment as exemplified by his book, Guns Germs, and Steel which earned him the Pulitzer Prize.
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| Burmese Python Photographed at Bardiya National Park, Nepal by Shadow Ayush Creative Commons Attribution-Share Alike 4.0 International |
This highly productive research line became possible because of advances made in the previous twenty years, largely by amateur herpetologists, in breeding snakes in captivity. This is one example of the upside of the commercial breeding of this species to be set against the awful practice of propagating colour varieties and the establishment of the Burmese Python as an invasive species in Florida.
Ambush predatory snakes like pythons spend long periods without food. Between their infrequent meals they shut down and reduce in size their digestive systems. But when food is caught, constricted and swallowed whole there is a burst of activity. The gut, liver etc grow rapidly while other organs like the heart are also involved in the rapid shift to digestion. Cardiac output—the volume of blood pumped per minute—increases to a greater extent than during exercise. This pioneering research has been continued by Stephen Secor, latterly at the University of Alabama, along with a number of collaborators.
When a snake ingests a whole animal, it gets the entire skeleton as well the nutrients contained in the other tissues. In other words it has to deal with very large amounts of calcium and phosphorus.
Although calcium plays a key part in providing strength to such structures as birds’ eggs, bone, and mollusc shells the process of biocalcification has long been of great interest simply because formation of these high-calcium structures and secretions, like milk, have to take place against a background of a low concentration of calcium in blood and a very much lower concentration inside cells. The concentrations are closely regulated and an excess in either compartment can be deadly even though large quantities of calcium have to pass through the cell involved in building the calcium-rich structures.
The latest discovery is described in a paper in Journal of Experimental Biology by Jehan-Hervé Lignot of the University of Montpelier, Robert Pope, an electron microscopist who also worked in France, and Stephen Secor. They found specialised cells in the intestinal epithelium that are involved in the production of calcium and phosphorus particles. The particles are released back into the gut and expelled as part of the faeces. In fasting snakes, the cells had no particles. Similarly, the cells of snakes fed meat bone-free sausages had no particles. However, when a calcium supplement was added the the bone-free sausages particles were present, as of course they were in snakes fed whole mice and rats.
Are the specialised cells in some way trapping excess calcium before it reaches the blood circulation? Or are they an excretory route activated by an excess calcium in blood? Clearly though, they are involved in removing calcium at times of excess input.
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| This is one of the photomicrographs from the paper by Lignot et al 2025. B. Alizarin red staining of a histological section of the proximal intestine. Arrow indicates a particle stained with Alizarine Red S. Scale bar: 100µm |
The authors have also found the particles in other snakes and in the Gila Monster. However, there have been no reports of such cells in the intestines of other vertebrates that ingest vertebrate prey whole. The question then of course is anybody looked, especially at times of really excessive calcium intake such that which could be obtained by supplemental feeding of calcium. They concluded:
It would be of great value to monitor a large-scale analysis within vertebrates that eat the entirety of their bony prey in order to identify how broadly distributed this cell type could be within the animal kingdom. Is it an ancestral cell type that remained within some snakes and lizards, or a modified enterocyte that could be highly plastic in nature? The presence of this cell type in fasting snakes with typically an empty crypt cell suggests that this is a specific cell type.
Amen to that.
*The first was exactly 55 years ago on the day I was drafting this article last week
Lignot J-H, Pope RK, Secor SM. 2025. Diet-dependent production of calcium- and phosphorus-rich‘spheroids’ along the intestine of Burmese pythons: identification of a new cell type? Journal of Experimental Biology 228, jeb249620. doi:10.1242/jeb.249620
