When a Python Has You Over For Dinner
Posted by Richard Conniff on December 7, 2013
Let’s say you’ve just been swallowed headfirst by a 15-foot-long Burmese python. The good news: Your worries are over. They’ve been over ever since those awkward getting-acquainted minutes when the snake was hanging on to you with its backward-raked fangs while squeezing the teeny-weeniest last bit of life from your lungs. Now you’re just a very large piece of meat, somewhat tenderized.
The snake, on the other hand, is revving up like a mothballed factory suddenly called back into full production. Over the next few hours, its heart will race up to 50 or 55 beats a minute, from 15 beats a minute during the sluggish month or so it has been lying around waiting for dinner to turn up. The amount of blood pushed out by each beat will increase five-fold. Heart, liver, kidneys, and small intestine will double in size, or more, to tackle the work at hand.
The 40-fold surge in the python’s metabolism is essential to digest the huge lump in its gut over the next five or six days, and it can’t stop until it’s done, says Stephen Secor, co-author on a study, published this week in Proceedings of the National Academy of Sciences, about how the python’s extraordinary digestive powers work. It’s a study that could have far-reaching implications for our understanding of how organs work and for the treatment of diseases like diabetes and heart failure.
But back to the original scenario, in which you become lunch. You probably saw the photograph that recently went viral of the python that had supposedly gobbled down a sleeping drunk beside a liquor store in India? A hoax, says Secor, who is a snake physiologist at the University of Alabama. The species in the photo lives in Indonesia, not India, and that huge mass of food swelling its gut was a deer, not a person.The truth is that even very big snakes almost never eat adult humans, says Secor. Though a child may occasionally make this unfortunate trip, the span of adult shoulders is generally just a little more than even the largest snakes can swallow. (UPDATE: I stand corrected. See below.)
But the python’s ability to perform digestive magic is nonetheless real. “They mostly eat smaller mammals and birds, says Secor. “But porcupines, pangolins—things you think ‘That’s a really tough meal’—they still eat ‘em.” The Burmese pythons that have invaded the Everglades will even take on alligators, he adds, “and they can digest them as easily as they digest a rat.”
Among the new study’s other results, Secor and his co-authors found that the arrival of a meal in the gut elicits “a rapid and massive” response from the snake’s digestive tract. Thousands of genes light up and go to work. One of Secor’s previous studies showed that even the number and variety of bacterial species in the gut seems to double from what’s present in a resting gut.
The new python paper, and another study published at the same time about the king cobra’s extraordinarily toxic venom, are the first ever to sequence a complete snake genome. The authors of the two studies collaborated, lining up parts of both snake genomes against each other and against the genomes of other vertebrates, to figure out how each snake acquired its extreme abilities.
The basic shift away from other vertebrates, and particularly from lizards, to “what makes a snake a snake, especially a snake that eats big things,” probably took place 100 to 150 million years ago, according to Todd Castoe, lead author on the python study and a biologist at The University of Texas at Arlington. Then, beginning 100 million years ago, a dramatic series of adaptations involving more than 500 genes rapidly changed python and cobra into their distinct forms.
Current thinking says big differences like this generally develop as a product of gene expression. That is, changes in when particular genes get turned on or off can produce major differences in form and function. But the snake studies call that idea into question. Both studies found far more extensive changes, involving not just the timing of gene expression, but the structure of the genome itself and also the proteins it produces. It was a major and rapid evolutionary reorganization.
Does that mean snakes will have the evolutionary nimbleness to adapt to rapid changes in the modern world? Not necessarily, Harvard evolutionary biologist Scott Edwards commented this week in New Scientist magazine. Even the rapid changes described in the two studies accumulated over millions of years. Whether snakes are “labile enough to resist all the challenges of habitat loss and climate change is unclear. It’s a different timescale.”
Secor believes, however, that the python study will help medical researchers understand the biochemistry of how organs function. That could eventually lead to treatments, he says, for heart disease, ulcers, intestinal malabsorption, Crohn’s disease, diabetes, and other conditions.
Experiments have already shown, for instance, that blood plasma from a fasting python has no effect on organ function in mammal species. But substitute blood plasma from a python that is revved up to digest its prey, and you can get human pancreas cells to increase insulin output by more than 20-fold.
With diabetes now afflicting about 285 million people worldwide—and rapidly rising—the python could turn out, against all odds, to be a lifesaver.
UPDATE: Herpetologist Harry Greene, author of the highly-praised new book Tracks and Shadows, has spent me a 2011 paper he co-authored in Proceedings of the National Academy of Sciences, including this doleful sentence:
‘Here, we report ethnographic observations of 120 Philippine Agta Negritos when they were still preliterate hunter–gatherers, among whom 26% of adult males had survived predation attempts by reticulated pythons. Six fatal attacks occurred between 1934 and 1973.”
Killing is not necessarily swallowing, of course. But the authors also comment:
Herpetologists have long claimed that giant serpents eat humans only under exceptional circumstances, but indigenous people living where large boas and pythons occur (Africa, Asia and nearby archipelagos, Australia, and South America) are well within the prey size range of those species; an adult male Agta would constitute ≤60% of the mass of a large female P. reticulatus, which is not a heavy meal by snake standards, and especially not for a species whose natural diet includes pigs weighing up to 60 kg.