Single-celled marine organisms offer a valuable window into major evolutionary transitions
We’re used to the saying “you are what you eat.” But you’re also how you eat – in other words, the physical form of living organisms adapts to optimize for nutrient intake.
But what are the earliest origins of this relationship between form and function, related to feeding? The study of flow physics holds the clue.
In a paper published by Nature Communications, researchers at Kanso Bioinspired Motion Lab at USC in collaboration with Marine Biological Laboratories use mechanistic models of ciliates — single-celled organisms that use cilia to either swim or generate feeding currents to capture prey — to demonstrate how living creatures have evolved for feeding efficiency. Cilia are hair-like micron-scale appendages that protrude from the cell surface and beat cyclically to generate flows. They preceded the evolution of muscles as one of the first “mechanical actuators.”
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?
The paper documents how ciliates designate a specific portion of the cell surface as a “mouth,” and how they use cilia to transport particles from the external environment to the mouth. Particularly, the paper focuses on optimal cilia coverage – cilia coverage that maximizes the transport of nutrients to the cell surface — and how it varies by life strategy – swimming or sessile. It turns out that the flow physics governing the transport of food particles to the cell surface explains the morphological diversity observed in ciliates. This is important because it implies that flow physics may have acted as a selective force in the evolution and morphological adaptations of ciliates.
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.
In sum – the evolution of phagotrophy by microbes required effective particle transport and ingestion, enabling the rise of ciliates as key grazers in aquatic ecosystems. The paper shows that the morphological adaptations of ciliates for feeding were shaped by hydrodynamic forces – revealing the role of flow physics in a major transition in the evolution of life on this planet.
Read the paper in Nature Communications.
Published on May 9th, 2025
Last updated on May 9th, 2025
