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Drinking in Snakes: Resolving a Biomechanical Puzzle

Video of drinking Agkistrodon piscivorus (A, B) and Nerodia rhombifer (C, D) during closed (A, C) and open (B, D) phases to show the nature of records analyzed for kinematics, performance, and, for C and D, pressure.

A Lehigh University research team lead by biologist David Cundall has found that some species of snakes drink using sponge-like properties in the skin folds of their lower jaw to absorb water.

The finding contradicts previous research—and conventional wisdom—that all snakes suck water through a tiny hole in their mouths like humans drink through a straw. The research may impact the fields of micro fluidics. Snakes have, it seems, solved a problem most other animal species still struggle with—beating gravity while taking a drink. The new “sponge” method of drinking may represent an evolutionary by-product of changes in the mouth driven by the demands of feeding.

“I find this method fascinating because it allows snakes to move water slowly,” said Cundall. “Most methods of drinking in the Animal Kingdom—imagine people, dogs or cats—require rather rapid movements, like lapping. You’re working against gravity. You have to do it faster than the water will fall.  Snakes have gotten around this problem.”

In 1993, Ken Kardong and Joseph Haverly at Washington State University found that boa constrictors sucked water in through a tiny hole in their mouths. This straw-like mechanism is also known as the buccal-pump model, which proposes that snakes alternate negative and positive pressures in the oral cavity to produce a pulsed inflow of water. In order to draw water in, snakes depress their lower jaw to create negative pressure. Then, as the mouth closes, the lower jaw and buccal floor rise and seal the margins of the mouth, which creates positive pressure and forces water into the pharynx.

Cundall, who has studied snakes for more than 40 years, began to question the buccal-pump model after finding that a number of species of snakes could drink without sealing the margins of their mouths. Without a seal, the mechanism for water flow to the pharynx was left in limbo. However, after examining recordings of muscle activity of four different species of snakes and noticing unsealed mouths, Professor Cundall and his team were able to conclude that mouth sealing, which is critical to the buccal-pump model, is incidental to many species.

“One thing that didn’t fit the model was that these species don’t seal the sides of their mouth,” said Cundall. “From there, it took a long time for me to realize that the anatomy of the system and the lining of the lower jaw suggested a sponge model.”

One of the reasons this method works is the bizarre way snakes eat, said Cundall. “Snakes spread the tips of their mandibles apart, and they manage to do this by unfolding a lot of the soft tissues, not stretching them as observers might conclude.  They are unfolding rather than stretching and it’s the folding of the lining of the lower jaw that creates the sponge-like morphology.”

To come to this conclusion, Cundall and his team used synchronized video and electromyographic recordings of muscle activity in three species and pressure recordings in the jaws and esophagus of a fourth species. By studying the kinematic data and performance data—combined with the muscle activity and pressure recordings of drinking—Cundall and his team were able to determine that water could be moved through sponge-like properties of the lower jaw.

Cundall works with a number of collaborators as well as undergraduate biology students to conduct his research, which has included studies on snake drinking, striking mechanics in boas, pythons, and vipers, the evolution of drinking mechanisms and even snake play. On this study, Cundall worked with undergraduates Doug Grapski and and Joe Constantino, as well as scientists from Brown University, Minot State University in North Dakota and Stony Brook University.

The mysterious new drinkers Cundall tested were the Agkistrodon piscivorus, or cottonmouth, a type of pit viper; Heterodon platirhinos, the Eastern hognose snake; Pantherophis spiloides, or gray rat snake; and Nerodia rhombifer, the diamond-backed watersnake.

Story by Jordan Reese

Posted on Thursday, February 23, 2012

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