Unicellular organisms form temporary groups

A team of researchers from the Marine Biological Laboratory (MBL) has uncovered a potential explanation for how early life might have transitioned from single-celled organisms to more complex multicellular forms. Their study focused on Stentors, large unicellular organisms that can temporarily form groups, suggesting that fluid dynamics might have played a role in this evolutionary shift.

Stentors use cilia to create feeding currents

Stentors are trumpet-shaped unicellular organisms found in ponds and lakes. They feed by using cilia—tiny hair-like structures around their mouths—to create water vortices that help them draw in small prey like bacteria. When placed in a laboratory setting, these organisms formed temporary colonies by positioning themselves side by side, creating stronger feeding currents together than they could alone.

Cooperation increases feeding efficiency

The study found that when Stentors grouped together, they could absorb twice as much water as when feeding individually. This increased water flow allowed them to capture more food and faster-moving prey. The organisms also changed partners, moving between neighbors to maximize their collective feeding efficiency, a behavior researchers humorously described as "she loves me, she loves me not."

Cooperation is temporary and resource-dependent

The researchers observed that when food became scarce, the Stentors separated and returned to solitary feeding. This suggests that cooperation was a flexible strategy, beneficial when resources were abundant but less so when they were limited. This dynamic might reflect an early evolutionary strategy, where temporary cooperation allowed organisms to survive better under favorable conditions.

Temporary cooperation may reflect early multicellularity

The study suggests that the temporary grouping of genetically distinct Stentors could mirror an early stage in the evolution of multicellular life. Around 2.5 billion years ago, organisms may have experimented with cooperation to maximize resources before evolving into stable, complex multicellular forms. This behavior of living together but not permanently might have been an essential step in that evolutionary journey.