In the arctic winter, penguins and polar bears store up huge amounts of fat but stay active. Hibernators such as squirrels and groundhogs fatten up for the winter then lower their metabolism by sleeping off.
But desert snakes don't display any such outward manifestation that might hint at how they manage to survive blistering summers while remaining relatively active.
Presenting a paper in an American Physiological Society session at Experimental Biology 2006, Marshall McCue notes that "birds, fish and mammals including humans have been studied in terms of food-deprivation, but surprisingly, the desert snakes haven't been studied in this regard considering that in the wild they'll go for up to two years without food. So McCue carefully studied 16 diamond-back rattlesnakes for 168 days, nearly 5 ½ months.
*Paper presentation: "Characterizing the starvation syndrome in the western diamond-back rattlesnake, a species well-suited to tolerate long-term fasting," 12:30 p.m.- 3 p.m. Monday April 3, APS Physiological Ecology & Evolutionary Physiology Section 492.4/board #C769. Research was by Marshall D. McCue, Department of Biology, University of Arkansas, Fayetteville.
First McCue came up with the phrase "starvation syndrome" to reflect the whole range of physiological coping mechanisms that the snakes employ. "Perhaps the greatest adaptation in this species is their ability to reduce energy expenditures by an average of 80% over 168 days of starvation," McCue said.
In addition to slowing down to conserve energy, McCue found that the snakes "chiefly 'fed' on their energy-rich lipid stores. The continual conversion of internal protein by these snakes into carbohydrates prevented glucose 'crashes' similar to those that can result from diabetic conditions in humans," he noted.
Another surprising finding was that despite literally eating themselves from within, the snakes actually grew over the 5 ½ months of starvation. Earlier reports on some starving reptiles said they actually shrank, but McCue found in this study of 16 diamond-backs – as well as another with rat snakes, but not pythons – measured growth. "This supports the long-standing hypothesis that a snake's length correlates with physiological fitness," McCue said. But beyond that and more.
In a sense, he says, even though the snake's mass is shrinking, as it must although it's increasing its own water content probably to maintain cellular shape, "it isn't panicking. Another line of evidence is the increased amount of relative calcium, which in fact doubled over the experiment. Because it takes more energy to grow than to eat yourself, the snake changes shape by reducing its girth and putting its resources into skeletal muscles and bone."
Among the many other metabolic changes, McCue pointed to an increase in fatty acids in the snakes. But as time went on, "the fatty acids became less saturated and they became polyunsaturated because in addition to beta-oxidation, they're undergoing some really dramatic changes as enzymes 'pick off' bits of hydrogen for energy."
In addition to the possible diabetes implications, McCue believes that all these metabolic changes point to ideas on "how we might be able to engineer diet so animals, and say humans in space, can tolerate food-deprivation better. Probably we can't do that with amino acid manipulation, but perhaps with fatty acids," he said. Another place where reduced food intake is vital, he adds, is in some post-operative recuperation where food intake needs to be strictly controlled.
Editor's Note: For further information or to schedule an interview with Marshall McCue, please contact Mayer Resnick at the APS newsroom @ 415.905.1024 (March 31-April 5); or 301.332.4402 (cell) or 301.634.7209 (office), mresnick@the-aps.org; or Christine Guilfoy at 978.290.2400 (cell) or 301.634.7253 (office).
The American Physiological Society was founded in 1887 to foster basic and applied bioscience. The Bethesda, Maryland-based society has more than 10,500 members and publishes 14 peer-reviewed journals containing almost 4,000 articles annually.
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A searchable online program for EB is at http://www.faseb.org/meetings/eb2006/call/default.htm
Experimental Biology is an annual scientific meeting convened by the Federation of American Societies of Experimental Biology, including the American Physiological Society (APS) and other biomedical societies. The meeting features "nominated" lectures, symposia, research presentations, awards, a job placement center, and an exhibit of scientific equipment, supplies, and publications. This year's participating Societies are APS, American Association of Anatomists, American Society for Biochemistry and Molecular Biology, American Society for Investigative Pathology, American Society for Nutritional Sciences, and the American Society for Pharmacology and Experimental Therapeutics.