For a creature made up of only a single cell, the stentor is a giant. This trumpet-shaped organism is among the largest unicellular organisms, stretching as long as a sharpened pencil tip. But sometimes it has a hard time vacuuming up the swimming bacteria and microscopic algae it eats to survive.
New research reveals that stentors, which are part of a group called protists, may address this challenge by eating “family style.” In a paper published on Monday in the journal Nature Physics, scientists shared the discovery that colonies of stentors can make water flow more quickly around them, helping them suck up more prey.
The new findings suggest that, although they lack neurons or brains, stentors can cooperate with one another.
“These single-cell organisms can do things that we assume are limited to more complex organisms,” said Shashank Shekhar, a biophysicist at Emory University in Atlanta who is the lead author of the new paper. “They form this higher order structure, like what we do as humans.”
Scientists believe that the ability of single-cell creatures to form groups was a key step that led to the eventual evolution of multicellular life on Earth. And the new findings spotlight the role played by physical conditions — and the interplay of predators and prey — in these cellular collaborations.
In the wild, stentors are found near the surface of ponds. The wider end of their bodies is fringed with ropelike cilia. These cilia can fluctuate in a wavelike pattern to generate water currents that sweep in prey.
To visualize these currents in the lab, Dr. Shekhar put drops of milk alongside stentors in a petri dish and then watched how the liquid flew under a microscope. “You see them create these swirls around their mouths that are just beautiful,” he said. He compared the movements to the whirling cosmos of van Gogh’s “The Starry Night.”
When food is scarce, stentors usually live alone. But when food is plentiful, they often congregate in writhing clusters. Little work has been done to explore why the protists form these colonies.
Dr. Shekhar and his colleagues first examined the interaction between pairs of stentors. Using microscope video footage, they measured the fluid dynamics as two stentors sucked in food particles in a petri dish.
The videos revealed an odd pattern: The stentors would drift toward each other before moving away, as if repelled by a magnet. “They constantly rotate between ‘I love you, I love you not,’” Dr. Shekhar said.
Further analysis then showed that stentor pairs were often in an unequal union, with one of the protists generating a stronger flow than its neighbor. When they got together, the resulting flow was the combined strength of both creatures. This meant that the weaker stentor benefited from the stronger one.
Such dynamics among the stentors inspire what Dr. Shekhar calls “promiscuous behavior.” When they gather in colonies, the stentors are constantly pairing with one another to find stronger partners and increase their feeding capabilities. This behavior increases the colony’s overall flow velocity, allowing the stentors to siphon in larger, fast-moving prey from farther away, and increase the nutrients consumed by the group’s members.
The formation of groups by single-cell organisms to improve survival is viewed as an important early step in the evolution of multicellularity. According to William Ratcliff, an evolutionary biologist at the Georgia Institute of Technology who was not involved in the new paper, once groups of predators like stentors formed, single-cell prey were more susceptible. To survive, the prey often teamed up themselves.
“The improved feeding efficiency by group predators like stentors selects for multicellularity in their prey,” Dr. Ratcliff said. “If you’re a single cell, you’re dinner. But if you can form large groups of cells, now you’re too big to eat.”
The new findings highlight how physical forces influence biological evolution.
“We always think about genes and chemicals, but there’s also a strong underpinning of physics in the development of multicellular life,” Dr. Shekhar said. “Even something like the flow of water could have affected evolution.”
