A joint study by Tel Aviv University and the University of Haifa set out to solve a scientific mystery: how a soft coral is able to perform the rhythmic, pulsating movements of its tentacles without a central nervous system. The study's findings are striking, and may even change the way we understand movement in the animal kingdom in general, and in the corals studied in particular.
The study was led by Elinor Nadir, a PhD student at Tel Aviv University, under the joint supervision of Prof. Yehuda Benayahu of the School of Zoology at Tel Aviv University and Prof. Tamar Lotan of the Department of Marine Biology at the Leon H. Charney School of Marine Sciences at the University of Haifa. The findings were published in the prestigious scientific journal PNAS.
An Orchestra Without a Conductor
The research team discovered that the soft coral Xenia umbellata - one of the most spectacular corals on Red Sea reefs - drives the rhythmic movements of its eight polyp tentacles through a decentralized neural pacemaker system. Rather than relying on a central control center, a network of neurons distributed along the coral's tentacle enables each one to perform the movement independently, while still achieving precise, collective synchronization.
"It's a bit like an orchestra without a conductor," explains Prof. Tamar Lotan of the School of Marine Sciences at the University of Haifa. "Each tentacle acts independently, but they are somehow able to 'listen' to each other and move in that perfect harmony that so captivates observers. This is a completely different model from how we understand rhythmic movement in other animals."
Testing the Limits of Coordination
Corals of the Xeniidae family are known for their hypnotic movements - the cyclic opening and closing of their tentacles. Until now, however, it was unclear how they perform this. To investigate, the researchers conducted cutting experiments on the coral's tentacles and examined how they regenerated and restored their rhythmic motion. To their surprise, even when the tentacles were cut off and separated from the coral - and even when further divided into smaller fragments - each piece retained its ability to pulse independently.
Ancient Genes, Modern Insights
Subsequently, the researchers conducted advanced genetic analyses and examined gene expression at different stages of tentacle regeneration after separation from the coral. They found that the coral uses the same genes and proteins involved in neural signal transmission in far more complex animals, including acetylcholine receptors and ion channels that regulate rhythmic activity. According to the researchers, this discovery suggests that the origin of rhythmic movements - familiar to us from those underlying breathing, heartbeat, or walking - is far more ancient than previously thought. The corals studied demonstrate how coordinated movement can emerge from a simple, distributed system, long before sophisticated control centers evolved in the brains of advanced animals.
Prof. Benayahu adds: "It is fascinating to reach the conclusion that the same molecular components that activate the pacemaker of the human heart are also at work in a coral that appeared in the oceans hundreds of millions of years ago. The coral we studied allows us to look back in time, to the dawn of the evolution of the nervous system in the animal kingdom. It shows that rhythmic and harmonious movement can be generated even without a brain - through remarkable communication among nerve cells acting together as a smart network. There is no doubt that this study adds an important layer to our understanding of the wonders of the coral reef animal world in general, and of corals in particular, and underscores the paramount need to preserve these extraordinary natural ecosystems."
