Flow physics of nutrient transport drives functional design of ciliates

Phagotrophy, the ability of cells to ingest organic particles, marked a pivotal milestone in evolution, enabling the emergence of single-celled eukaryotes that consume other organisms and leading to multicellular life. However, reliance on food particles also created a mechanical challenge—how to coordinate the transfer of particles from the exterior environment to the cell interior? Here, we investigate this important link using mechanistic models of ciliates, a clade of single-celled eukaryotes that either swim or attach and generate feeding currents to capture prey. We demonstrate that ciliates optimize their feeding efficiency by designating a specific portion of the cell surface as a ‘mouth,’ and optimal cilia coverage varies by life strategy: for sessile ciliates, prey encounter is most efficient when cilia are arranged in bands around oral structures while ciliates that swim display diverse ciliary arrangements that meet the cell’s nutritional needs. Importantly, beyond a threshold of doubling nutrient uptake, further increases in feeding flux do not seem to be a dominant selective force in cell design.