Cellular multifunctionality in the muscle activity of Hydra vulgaris

Summary As a cnidarian, Hydra has an anatomically simple neuromuscular system likely similar to those of ancestral species, and its study could provide insights on the design logic and function of animal body plans throughout evolution. Here we have used calcium imaging to map the activity of the entire epitheliomuscular system of living Hydra in mounted preparations. We find seven basic spatiotemporal patterns of activation, with fast and slow kinetics of initiation and propagation. Contrary to previous assumptions, both endodermal and ectodermal epitheliomuscular tissues are systematically activated jointly during contractions, in spite of their muscle fibers being orthogonally arranged. We also find that individual cells surprisingly participate in multiple patterns, using different kinetics of activation. Our results reveal that Hydra’s epitheliomuscular tissue is a multifunctional system that can be flexibly reconfigured to generate different spatiotemporal activity patterns, enabling a structurally simple design to implement a varied behavior output.