Saturday, August 18, 2007

How snakes starve to live

New York, Aug 17 (IANS) Mystery shrouding a snake's ability to go without food for nearly two years may have been finally uncovered with researchers claiming to have cracked the mechanism behind their survival despite starvation.

The research, which reveals some previously unknown serpentine tricks, sheds light on how serpents managed to drag on since before the days of the dinosaur Tyrannosaurus rex, biologists were quoted as saying in the Nature magazine.

Biologist Marshall McCue at the University of Arkansas, Fayetteville, kept ratsnakes, pythons, and rattlesnakes in cages where they could not alter their activity levels - they were forced to be inactive.

They were also unable to reduce body temperature, stuck with the laboratory temperature of a steady 27C. The animals were then starved for a period of up to 168 days.

McCue measured the animals' oxygen consumption and found that they had somehow managed to reduce their resting metabolic demands by up to 72 percent.

'We had no idea that these animals could reduce their metabolic rates lower than their standard resting rate,' says McCue. 'It would seem that their pilot light, which we already thought to be as low as possible, actually goes much lower.

'In most starving animals, allowing lipid (the compound that make up fat) levels to fall below 10 percent body mass is a death sentence,' says McCue. But snakes were able to go down to five percent body fat before making a switch to protein consumption, he found, letting them hold on for longer without food.

'Even then, consuming their own proteins had little effect on their health because they had slowed down their metabolism so drastically,' he says. 'The ability to selectively utilise lipids at low levels, thereby conserving structural proteins, could be a key breakthrough in understanding starvation survival,' says physiologist Anthony Steyermark of the University of St Thomas, Minnesota.

How the snakes were lowering their metabolic rates, without lowering their temperature - and while staying alert enough to attempt to bite their captor - is a mystery.

McCue thinks the snakes may be reducing the density of energy-generating cell machinery called mitochondria in highly active tissues such as those in the liver and heart.

In addition, the snakes had a cunning way to stretch out their resources while enduring starvation.

All animals burn lipids - the compounds that make up fat - for energy when they run out of food.

But lipids have some essential functions in the body, forming crucial parts of cells and organs needed for nutrient transfer, for example. So as starvation progresses and fat reserves run low, most animals turn to protein in the body and begin using that as an energy resource instead. This essentially means that they begin to digest themselves - a process that can only be tolerated for a short while before resulting in death.

Biologists have long argued that there are two main tactics used by animals to weather a period of starvation.

The core body temperature can be reduced, as is the case in penguins that go through torpor to reduce their calorie use during the winter. Hibernating animals such as hedgehogs utilise another method - they stock up on food and then reduce activity levels. Some species, including polar bears, do both.

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