A distributed neural “pacemaker” system has been discovered in the Red Sea Xenia umbellata: each arm beats independently but synchronizes with the others; the findings were published in PNAS and may change the understanding of rhythmic movement in evolution
A joint study by Tel Aviv and Haifa universities attempted to solve the scientific mystery: how soft coral manages to perform rhythmic pulsating movements of its arms without a central nerve center. The research findings are very surprising and may even change the way we understand movement in the living world in general and in the corals under study in particular.
The research was led by Elinor Nadir, a doctoral student at Tel Aviv University, under the joint supervision of Prof. Yehuda Benyahu. from the School of Zoology in the George S. Wise Faculty of Life Sciences at Tel Aviv University, Together with Prof. Tamar Lotan from the Department of Marine Biology, from the Czarny School of Marine Sciences, University of Haifa. The study was published in the prestigious scientific journal PNAS.
Like an orchestra without a conductor
As part of the study, the team of researchers revealed that the soft coral Xenia umbellata, one of the spectacular corals in the Red Sea reefs, activates the rhythmic movements of its eight polyp arms using a distributed neural pacemaker system. This means that it does not have a control center that manages the action, but rather a network of neurons scattered along the coral's arms, with each arm performing the movement independently, yet they all manage to synchronize with each other.
"It's a bit like an orchestra without a conductor," explains Prof. Tamar Lotan from the School of Marine Sciences at the University of Haifa: "Each arm operates independently, but somehow they manage to 'listen' to each other and move in perfect harmony that is so intriguing to the observer. This is a completely different model from the way we understand rhythmic movement in other animals."
"The studied coral allows us to look back in time, to the beginning of the evolution of the nervous system in the living world"
The ancestor of the pacemaker
Corals from the Xenia family are known for their hypnotic movement – the cyclical opening and closing of their arms. Until now, it was unclear how they do this. The researchers conducted experiments cutting the arms of the coral and examined how they regenerate and return the pulsations of movement to themselves. To their surprise, even when they cut the arms and separated them from the coral, or even cut pieces from them – each segment retained its ability to pulsate on its own.
The researchers then performed advanced genetic analyses and examined gene expression during the different stages of regeneration of the tentacles that were separated from the coral. They discovered that the coral uses the same genes and proteins involved in transmitting nerve messages in much more advanced animals, including acetylcholine receptors and ion channels that determine rhythm. According to the researchers, the discovery suggests that the origin of rhythmic movements, familiar to us from the processes of breathing, heartbeat, or walking, is much older than we thought. The corals under study illustrate how movement can arise from a distributed and simple system, long before sophisticated control centers were created in the brains of advanced animals.
Prof. Benyahu adds: "It is fascinating to come to the conclusion that the same molecular components that activate our pacemaker also operate in a coral that appeared in the oceans hundreds of millions of years ago. The coral being studied allows us to look back in time, to the beginning of the evolution of the nervous system in the living world. It shows that it is possible to produce rhythmic and harmonious movement even without a brain, with the help of spectacular communication between nerve cells that work together like a smart network. There is no doubt that the research adds an important layer to understanding the wonders of the coral reef's animal world in general and of corals in particular, and raises the supreme need to preserve these wonderful natural values."
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