Why Does A Starving Diamond-Back Continue To Grow? Optimism!

Faced with up to two years without food, rattlesnake cuts metabolism by 80%, changes energy source to lipids

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Hints of diet engineering in diabetes, post-recovery and space travel

SAN FRANCISCO (April 4, 2006) – Nearly every organism has developed its own mechanism to cope with starvation or reduce food availability, whether for hours or months.

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, and food shortages 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, 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 monitored 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 each animal employs. “Perhaps the greatest starvation adaptation in rattlesnakes is their ability to reduce routine energy expenditures by an average of 80% over 168 days of starvation,” McCue said.

Turning protein into carbs prevents diabetes-like glucose “crashes”

In addition to slowing down metabolism to conserve energy, McCue found that the snakes “chiefly ‘fed’ on their energy-rich lipid stores. Nevertheless, continual conversion of internal protein by these snakes into carbohydrates prevented glucose ‘crashes’ similar to those that can result from starvation and diabetic conditions in humans,” he noted.

Another surprising finding was that despite literally eating themselves from within, the snakes actually grew in length over the 5 ½ months of starvation. Earlier reports on some starving reptiles said they shrank, but McCue found in this study of 16 diamond-backs – as well as other studies with rat snakes, but not pythons – growth continued during starvation. “This supports the hypothesis that length in some snakes may be strongly correlated with its fitness,” McCue said.

Because it takes more energy to grow than to simply eat yourself, the snake changes shape by reducing its girth and putting its resources into skeletal muscles and bone.” Another new line of evidence that starving snakes are devoting resources to growth is the increased relative calcium levels in the body. In addition to increasing length, these animals apparently reduce expected rates of mass loss by increasing the water content in retained tissues. “This phenomenon is likely beneficial because it serves to maintain cellular sizes during starvation” according to McCue.

Some of retained fatty acids actually become “polyunsaturated”

Among many other metabolic changes detected, McCue pointed to a general decrease in fatty acids in the snakes. But as time went on, “the retained fatty acids became less saturated and many became polyunsaturated because in addition to beta-oxidation, they’re undergoing some really dramatic changes as ‘desaturase 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 perhaps humans in space, can tolerate food-deprivation better. We probably 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.

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Editor’s Note: For further information or to schedule an interview with Marshall McCue, please contact Donna Krupa at the APS newsroom @ 415.905.1024 (March 31-April 5); or (703) 967-2751 (cell) or (301) 634-7209 (office), dkrupa@the-aps.org; or Christine Guilfoy at 978.290.2400 (cell) or 301.634.7253 (office).

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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.

APS  provides a wide range of research, educational and career support and programming to further the contributions of physiology to understanding the mechanisms of diseased and healthy states. In May 2004, APS received the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring (PAESMEM).

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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.

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Comparative At comparative meeting: using stable isotope label metabolic tracers specifically leucene and glucose to examine where these materials are allocated in various tissues in three species of pit vipers.