New research sheds light on animal locomotion

Posted on Monday, December 2, 2019

Understanding how centipedes move from walking to swimming

Animals move adaptively in various environments by flexibly coordinating their body and limbs. In particular, amphibious animals, such as salamanders and certain types of fish, possess outstanding adaptability: They can move between land and water by changing their body coordination patterns in real time. However, the essential mechanisms underlying how amphibious animals coordinate their body and appendages during adaptive locomotion have long been elusive.

That is until now. Researchers at Tohoku University, the Swiss Federal Institute of Technology in Lausanne, the University of Ottawa, and Hokkaido University, with the support of the Human Frontier Science Program, have, for the first time, decoded the flexible motor control mechanism underlying amphibious locomotion (the action to walk on land and to swim in water) in centipedes.

The team of researchers, including Emily M. Standen, Associate Professor in the Department of Biology at the University of Ottawa, focused on a specie of centipede, named Scolopendra subspinipes mutilans.  This centipede walks on land by coordinating its many legs, but when put in water, it folds its legs and swims by bending the body trunk similar to an eel. The homogeneous and segmented body structure of the centipede facilitates the visualization of behavioral changes as it crosses between terrestrial and aquatic environments, making it an excellent animal model.

Researchers led by Professor Akio Ishiguro of the Research Institute of Electrical Communication at Tohoku University, observed intact and nerve transected animals transitioning between walking and swimming and hypothesized that interactions between the central nervous system, the peripheral nervous system, the body, and the environment can explain gait transitions.

They hypothesized that walking or swimming signals generated in the brain are sent posteriorly via distributed neural networks belonging to the central nervous system and located along the body; these brain signals can be overridden by sensory signals felt by the peripheral nervous system of the legs when they touch the ground during walking. The researchers described this multiple-signal mechanism mathematically and reproduced the behavior of centipedes in different situations through computer simulations.

Photographs for the transition from swimming to walking in centipede

Photographs for the transition from swimming to walking in centipede (Scolopendra subspinipes mutilans). While it folds the legs and moves by undulating the body trunk in water (left in each photograph), it transitions to walking by coordinating leg movements on land (right in each photograph).

Dr. Standen worked with the Hokkaido and Tohoku teams to analyze live centipede data and discuss possible control systems that could provide that outcome. This input helped to guide the mathematical model developed by the Tohoku and EPFL teams.

“The big message here is that walking in centipedes can be controlled entirely by local sensory feedback from the legs, in the absence of the brain, while swimming requires top down brain signals to occur,” explained Dr. Standen. “This suggests two distinctly different roles of sensory feedback for swimming compared with walking. This adds information about how animal nervous systems can integrate and use sensory feedback to display functional locomotion.”

The researchers hope that this finding provides insights into the essential mechanism underlying adaptive and versatile locomotion of animals. It will also help develop robots that can move on various environments by flexibly changing body coordination patterns.

Their research Decoding the essential interplay between central and peripheral control in adaptive locomotion of amphibious centipedes was published on December 2, 2019, in Scientific Reports.

VIDEO: Navigating Land and Water: How Centipedes Walk and Swim (Available in English only)

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Justine Boutet
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