Nothing sets a Burmese python's heart beating quite like settling down to digest a nice meal. Pythons consume their food in a single gulp, which is why their heart rate rockets; digesting an intact meal, skin and all, takes a lot more effort than the finely minced mouthfuls that we swallow. Which made Stephen Secor wonder just how much energy a hungry python has to invest in digestion, before the prey pays back. Secor fed young pythons a range of specially selected rat- like meals and monitored them while their digestive juices got down to business, to find out how much effort it takes a python to get the most from a meal (p. 1621).
First, he wanted to see exactly how the snakes digested a large rat after swallowing it headfirst. X-raying the satisfied reptiles every day, he watched the meal as it slowly dissolved, skull first followed by the shoulders and body through to the tip of the tail six days later. And when he investigated the reptiles' stomach contents once the skeleton had vanished from the stomach, the only part of the rat that remained were tufts of hair.
Next Secor monitored the snake's stomach pH after a heavy meal. He attached a minute pH electrode to a rat's head, and fed the animal to the snake. The snakes wolfed down the rat, electrode and all. He adds that although they seemed a little distracted at first by the wire protruding from their mouths, within a matter of minutes, the snakes had lost interest in it, and settled down. Once the pH meter was in place, Secor and python couldn't be parted as he monitored the stomach pH round the clock. During the first day, the pH hardly fell below 7.5, but after 18 hours it plummeted to 1.5. What impressed Secor was how the snake maintained the stomach's extremely acidic environment for days, until the meal had moved on to the small intestine. As quickly as it had begun producing acid, the snake's stomach stopped, and the pH rose again. But how much energy were the pythons' expending by pumping hydrochloric acid and enzymes into the stomach?
Secor explains that when an animal feeds, its metabolic rate increases from the moment it swallows food, and remains elevated while the meal is digested, absorbed and, eventually, the released nutrients are incorporated into the animal's own body. How much of the increase was down to the stomach alone, wasn't clear. Secor fed pythons meals including intact rats, ground rats where the stomach hardly had to do any work. He even by-passed the stomach entirely and delivered rat-slurry directly to the small intestine. Then he measured the reptiles' metabolic rates.
The metabolic rate of the rat-fed pythons was three times higher than in the animals whose stomachs had been bypassed. And when he calculated the stomach's contribution to the snake's investment in its meal, it accounted for over 50%! How the python sustains this incredible metabolic leap for days on end isn't clear, but the next time you see a dozy looking python digesting its dinner, don't be fooled; according to Secor `they are on fire!'
- © The Company of Biologists Limited 2003