updated 4/7/2009 12:30:31 PM ET 2009-04-07T16:30:31

How does a worm crawl? And how does it swim? The answer is simple: The same way.

A new study of the worm C. elegans finds these lowly creatures crawl and swim using the same gait, overturning the widely accepted belief that these two behaviors are completely different.

The tiny worm, just a millimeter long, was the very first animal species to be completely genetically sequenced. It has many of the same genes that are found in humans, and so is used by scientists as a model system to gain a fundamental understanding of the basic principles of life.

In fact, the human brain's origins can be traced back to the central nervous system of worms, a study in 2007 concluded.

C. elegans is so simple it has no brain, only a minimal nervous system of 302 nerve cells (as opposed to the 100 billion or so in the human brain).

Yet the worm exhibits a wide range of behavior, including foraging, learning, memory and even social behavior. Scientists are fascinated with this tiny worm, anticipating that this will be the first animal species to be completely understood. (See a video.)

That's one reason the new finding matters.

"Our discovery suggests that it's important to study the function of the worm's nervous system in a range of environments, where the mode of operation of the nervous system and the specific role of individual genes may be more apparent," said Netta Cohen of the University of Leeds in the UK.

In its natural habitat, C. elegans can encounter a range of environments where its motion can be quite varied — from muddy water and moist surfaces in dry ground to the center of rotten fruit, where it likes to dine.

The worm's swimming and crawling, observed in different environments, look so distinct, there was a long-held consensus that these are separate gaits — as with horses, where galloping and trotting are entirely different motions.

Using a combination of experimental laboratory work and computer simulations, Cohen's team found otherwise.

"We raised the question of how such a minimal nervous system can exhibit different behaviors and instantly switch between them," Cohen said. "Our finding is the first unified description of a whole range of behaviors and should hopefully make the modeling of this animal more accessible."

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