Foodfree growth.

Animals endure famine--some more successfully than others--by cannibalizing their own tissues. Rattlesnakes, among the champions, can survive more than 2 years between meals.

To understand how, evolutionary physiologist Marshall McCue of the University of Arkansas in Fayetteville starved 2-yearold rattlers for more than 5 months and measured changes in their bodies. To his surprise, he found that although the snakes continued to move about and even to grow, "they undergo an almost hibernation-like drop in metabolic rate." In this state, the snakes consumed just 20 percent as much oxygen as when they were well fed, says McCue.

After initially putting Western diamondbacks (Crotalus atrox) on a regular feeding regimen of one mouse every 2 weeks for 6 months, McCue suddenly gave them only water. He reports that the animals relied largely on stored fats to survive.

But the rattlers' bodies didn't treat all fats equally. The snakes preferentially burned medium-chain fatty acids, while conserving longer fatty acids. The snakes also appeared to derive some energy by desaturating--or removing hydrogen atoms from--their stored long-chain fatty acids. Rarely, McCue found, did the snakes break down muscle protein for energy as some other malnourished animals do.

Throughout the prolonged fast, the snakes slimmed down. "However, in the wild, we regularly see snakes much skinnier than these," McCue says. Most amazing: Despite going months without food, the snakes' bodies, excluding their rattles, actually lengthened by 2 to 3 centimeters. "This is significant," McCue notes, because it reflects growth comparable "to what might be experienced with normal feeding."--J.R.