Cooperative hydrodynamics accompany multicellular-like colonial organization in the unicellular ciliate .

Evolution of multicellularity from early unicellular ancestors is arguably one of the most important transitions since the origin of life. Multicellularity is often associated with higher nutrient uptake, better defense against predation, cell specialization and better division of labor. While many single-celled organisms exhibit both solitary and colonial existence, the organizing principles governing the transition and the benefits endowed are less clear. Using the suspension-feeding unicellular protist , we show that hydrodynamic coupling between proximal neighbors results in faster feeding flows that depend on the separation between individuals. Moreover, we find that the accrued benefits in feeding current enhancement are typically asymmetric- individuals with slower solitary currents gain more from partnering than those with faster currents. We find that colony-formation is ephemeral in and individuals in colonies are highly dynamic unlike other colony-forming organisms like . Our results demonstrate benefits endowed by the colonial organization in a simple unicellular organism and can potentially provide fundamental insights into the selective forces favoring early evolution of multicellular organization.