Coordinated Behavior in Choanoflagellates Provides Evolutionary Clues

A new study published in Science Advances reveals evidence of electrical signaling and coordinated behavior in choanoflagellates, the closest living relatives of animals. This elaborate example of cell communication offers key insights into the early evolution of animal multicellularity and nervous systems.

Researchers from the Burkhardt group at the Michael Sars Centre, University of Bergen, uncovered a remarkable diversity of behaviors within the rosette-shaped colonies of the choanoflagellate Salpingoeca rosetta - and the small organisms held even more surprises. "We found communication among the cells of the colonies, which regulates shape and ciliary beating across the rosette," explains first author Jeffrey Colgren. "We didn't have clear expectations of what we would see in the cultures before putting them under the microscope, but when we did, it was very exciting."

Multicellularity is a defining characteristic of all animals, enabling them to interact with their environment in unique ways by integrating the input of highly specialized cell types, such as neurons and muscle cells. For choanoflagellates, flagellated organisms found in marine and aquatic environments all over the globe, the boundary between uni- and multicellularity is less distinct. Some species, including S.rosetta, exhibit complex life cycles that include colonial stages. While the colonies are formed through cell divisions, much like the developing embryos of animals, they lack specialized cell types and are more akin to a group of individual cells than a cohesive organism.

S. rosetta is a powerful model for investigating the emergence of multicellularity during animal evolution. Since our study reveals that colonial choanoflagellates coordinate their movements through shared signaling pathways, it offers fascinating insights into early sensory-motor systems."

Pawel Burkhardt, Last Author

Using a newly developed genetic tool that enables visualization of calcium activity in S. rosetta, the team found that the cells synchronize their behavior through voltage-gated calcium channels, the same type of channels used by animal neurons and muscle cells. "This evidence of how information flows between cells in choanoflagellate colonies demonstrates cell-cell signaling at the cusp of multicellularity", says Colgren. Strikingly, the discovery suggests that the ability to coordinate movement at the cellular level predates the first animals.

Moving forward, the team plans to further investigate how signals propagate between cells and whether similar mechanisms exist in other choanoflagellate species. "The tools developed and findings from this study open up a lot of new and interesting questions",

Colgren concludes. "We're really excited to see where ourselves and others take this in the future."