For most of us, settling down to digest a hearty breakfast isn't the most eventful part of the day. But for many snakes, every meal is breakfast, and digesting unchewed mouthfuls is probably the most energetic thing they do; their metabolic rates rocket. Knowing that a digesting snake has a souped-up metabolic rate, Glenn Tattersall wondered whether digestively active snakes warm up too? After all snakes are not endothermic; they don't normally generate inner warmth. Heading south to Brazil with an infrared camera, Tattersall decided to put well-fed snakes on the spot, and ask them whether they warmed when fed (p. 579).
But when Tattersall arrived at Augusto Abe and Denis Andrade's Rio Claro lab, he didn't find a colony of good-natured snakes waiting to work with him. Instead, he had the pick of a colony of Crotalus durissus South American rattlesnakes, with bad attitudes.
Unphased by the prospect of working with the venomous reptiles, Tattersall set about preparing small and large mouse meals ready to feed the snakes; but he hadn't banked on the reptile's contrary character. Some of the snakes tucked into their mice, while others didn't finish their portion, or simply ignored them. But after a day, enough snakes had satisfied their hunger for Tattersall to begin tracking the reptile's body temperatures while they patiently digested their snacks.
Over the first few hours, Tattersall didn't see much change through the lens of his infrared camera; the snakes blended in well with the thermal background. But after half a day, the snakes began to glow, and after 24 hours, they were clearly 1.5°C warmer then the background temperature. And when he tested the heat given off by a dead mouse after the same time, the mammal's corpse was stone cold. Tattersall wasn't seeing heat produced by a decaying mouse's body; this was a real increase in the reptile's body temperature, entirely due to the rise in their metabolic rate. Once, he even saw discrete hot spots on a snake's body, perfectly matching the number of mice that the reptile had swallowed the day before.
Delighted that the infrared camera had picked up the snake's postprandial hotspots, Tattersall began looking to see if the snakes had any other curious thermal habits. Noticing that the animals always rattled their tails vigorously whenever Simone Brito walked into their room, Tattersall trained the camera on the snake's tails. The shaker muscle lit up with warmth, while the air filled rattle stayed cool.
Having found that rattlesnakes warm after a mouthful of mouse, Tattersall and Brito are keen to see whether pythons do too. They explain that when a rattlesnake swallows its prey, the venom that killed the hapless victim often contributes to the snake's digestive task, breaking the rodent down from the inside. Pythons on the other hand, rely entirely on their gastric juices to digest their breakfasts. But as Tattersall had to return to his lab in Canada, Brito has been left wondering whether the python's extra internal effort might raise the snake's temperature even higher.
- © The Company of Biologists Limited 2004