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

Many single-celled organisms exhibit both solitary and colonial existence. An important step towards multicellularity, which is associated with benefits such as enhanced nutrient uptake, was the formation of colonies of unicellular organisms. However, the initial drivers that favoured individual cells aggregating into more complex colonies are less clear. Here we show that hydrodynamic coupling between proximate neighbours results in faster feeding flows for neighbouring ciliates, such that individuals within a dynamic colony have stronger average feeding flows than solitary individuals. Flows generated by individuals acting together reach higher velocities, thus allowing access to a wider range of prey resources than individuals acting on their own. Moreover, we find that accrued feeding benefits are typically asymmetric: whereas all individuals benefit from acting together, those with slower solitary currents gain more from partnering than those with faster currents. We find that colonial organization in simple unicellular organisms is beneficial for all its members. This provides fundamental insights into the selective forces favouring the early evolution of multicellular organization.