Flow coupling and stochastic oscillations amplify feeding currents in Stentor colonies

Stentor coeruleus is a ciliated protist commonly found in freshwater lakes and streams. Stentor individuals attach their base to organic surfaces and form colonies. Each stentor in the colony has a horn-shaped body, that sways from side to side, with a band of beating cilia near its "head" that generates feeding currents and brings nutrients and particulates to the cell. Here, we investigate the effects of colony formation and stochastic body oscillations on colonial versus solitary feeding. We find that flow coupling between proximal neighbors results in faster feeding flows that depend on the separation between individuals, and that the accrued benefits are typically asymmetric in favor of weaker stentors. Additionally, we find that the stochastic oscillations of individuals within the colony lead to, on average, stronger feeding currents. Our results demonstrate how the interplay between two complementary physical mechanisms, flow coupling and stochastic body oscillations, boost colonial over solitary foraging. These findings highlight the benefits endowed by colonial organization in a simple unicellular organism and can potentially provide fundamental insights into the selective forces favoring the early evolution of multicellular organization.