Researchers examine mechanical bases for the emergence of undulatory swimmers

Jun 24, 2013

How do fish swim? It is a simple question, but there is no simple answer.

Researchers at Northwestern University have revealed some of the that allow fish to perform their complex movements. Their findings, published on June 13 in the journal PLOS Computational Biology, could provide insights in and lead to an understanding of the of movement and development of bio-inspired .

"If we could play God and create an undulatory swimmer, how stiff should its body be? At what should its body undulate so it moves at its top speed? How does its brain control those movements?" said Neelesh Patankar, professor of mechanical engineering at Northwestern's McCormick School of Engineering and Applied Science. "Millennia ago, undulatory swimmers like eels that had the right mechanical properties are the ones that would have survived."

The researchers used to test assumptions about the preferred evolutionary characteristics. For example, species with low frequency and high body stiffness are the most successful; the researchers found the optimal values for each property.

"The stiffness that we predict for good swimming characteristics is, in fact, the same as the experimentally determined stiffness of undulatory swimmers with a backbone," said Amneet Bhalla, graduate student in mechanical engineering at McCormick and one of the paper's authors.

"Thus, our results suggest that precursors of a backbone would have given rise to animals with the appropriate body stiffness," added Patankar. "We hypothesize that this would have been mechanically beneficial to the evolutionary emergence of swimming ."

In addition, species must be resilient to small changes in physical characteristics from one generation to the next. The researchers confirmed that the ability to swim, while dependent upon mechanical parameters, is not sensitive to minor generational changes; as long as the body stiffness is above a certain value, the ability to swim quickly is insensitive to the value of the stiffness, the researchers found.

Finally, making a connection to the neural control of movement, the researchers analyzed the curvature of its undulations to determine if it was the result of a single bending torque, or if precise bending torques were necessary at every point along its body. They learned that a simple movement pattern gives rise to the complicated-looking deformation.

"This suggests that the animal does not need precise control of its movements," Patankar said.

To make these determinations, the researchers applied a common physics concept known as "spring mass damper"—a model, applied to everything from car suspension to Slinkies, that determines movement in systems that are losing energy—to the body of the fish.

This novel approach for the first time unified the concepts of active and passive swimming—swimming in which forcing comes from within the fish (active) or from the surrounding water (passive)—by calculating the conditions necessary for the fish to swim both actively and passively.

Explore further: Birds 'weigh' peanuts and choose heavier ones

More information: "A Forced Damped Oscillation Framework for Undulatory Swimming Provides New Insights into How Propulsion Arises in Active and Passive Swimming," PLOS Computational Biology, 2013.

Related Stories

Recommended for you

Birds 'weigh' peanuts and choose heavier ones

19 hours ago

Many animals feed on seeds, acorns or nuts. The common feature of these are that they have shells and there is no direct way to know what's inside. How do the animals know how much and what quality of food ...

Estuaries protect Dungeness crabs from deadly parasites

May 22, 2015

Parasitic worms can pose a serious threat to the Dungeness crab, a commercially important fishery species found along the west coast of North America. The worms are thought to have caused or contributed to ...

An evolutionary heads-up—the brain size advantage

May 22, 2015

A larger brain brings better cognitive performance. And so it seems only logical that a larger brain would offer a higher survival potential. In the course of evolution, large brains should therefore win ...

Our bond with dogs may go back more than 27,000 years

May 21, 2015

Dogs' special relationship to humans may go back 27,000 to 40,000 years, according to genomic analysis of an ancient Taimyr wolf bone reported in the Cell Press journal Current Biology on May 21. Earlier genome ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.