Multisensory decision-making drives distinct aggregations in Paramecium: New collective phenomena and dynamics

We combine experimental characterizations and numerical simulations to explore collective behaviors of the model ciliate Paramecium. A novel collective structure named the icicle phenomenon is experimentally identified when paramecium populations undergo rapid proliferation, featuring vertical elongated cell aggregates accumulating near the water surface and growing downward. Three fundamental innate behaviors of paramecium-chemotaxis, negative gravitaxis, and avoiding reaction-are proven to be the indispensable drivers of this emergent pattern. Different from classic Active Brownian Particle and Run-and-Tumble models, our numerical framework incorporates a full active sensing-motility actuation strategy that mimics the microbe’s real environmental sampling and signal decision process. Corresponding molecular dynamic simulations successfully replicate the experimentally observed horizontal aggregation and icicle collective patterns, and clarify the synergistic interplay of multiple taxic behaviors in generating large-scale self-organized structures.