For creatures made up of only a single cell, the Stenter is a giant. This trumpet-shaped organism is one of the largest single-celled organisms, stretching at the tip of a sharp pencil. However, sometimes it can be difficult to vacuum the swimming bacteria and microscopic algae that it eats to survive.
A new study reveals that Stentors, part of a group called Protists, could address this challenge by eating “family style.” In a paper published Monday in the journal Nature Physics, scientists shared the finding that stentor colonies can drain water around them more quickly, helping them suck more prey.
New findings suggest that stenters can cooperate with each other, although there is a lack of neurons and brains.
“These single-cell organisms can do what appears to be confined 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 structure, as we do as humans.”
Scientists believe that the ability of single-cell creatures to form groups is a critical step leading to the ultimate evolution of multicellular life on Earth. And new discoveries highlight the role played by physical states and predator-prey interactions in these cellular collaborations.
In the wild, stenters are found near the surface of the pond. At the wider ends of their bodies, there are cilia, like loppella. These cilia fluctuate in wave-like patterns and can produce water streams that clean prey.
To visualize these currents in the lab, Dr. Shekhar placed a drop of milk in a Petri dish along with a stenter and saw how the liquid flew under the microscope. “You see them just make these swirls around their beautiful mouths,” he said. He compared movement with the swirling cosmos in Van Gogh's “Starry Night.”
If food is lacking, the stent ter usually lives alone. However, when food is plentiful, they often gather in writhing clusters. There is little work done to explore the reasons why these colonies form.
Dr. Shekhar and his colleagues first examined the interactions between pairs of stentters. Using microscope video footage, two stenters were sucked into food particles in a Petri dish measured the liquid dynamics.
The video reveals some strange patterns. The stenters float towards each other before they leave, as if they were repelled by a magnet. “They are always spinning between 'I love you, I don't love you,'” Dr Shekhar said.
Further analysis subsequently showed that the stentol pairs are often in unequal connections, with one of their protists producing stronger currents than their neighbors. When they gathered, the resulting stream was a combination of the strengths of both creatures. This meant that the weaker stenters benefited from the stronger ones.
Such dynamics between stenters stimulate what Dr. Shekhar calls “indiscriminatory behavior.” When they gather in the colony, the stenters are always paired with each other, finding stronger partners and increasing their feeding ability. This behavior increases the overall flow rate of the colony, allowing the stenter to suck up with faster prey, even further distant sizes, increasing the nutrients consumed by group members.
The formation of groups by single-cell organisms to improve survival is considered an important early stage in the evolution of multicellularity. According to Georgia Tech evolutionary biologist William Ratcliffe, who was not involved in the new paper, but single-cell prey was more sensitive when groups of predators, such as stentters, formed. To survive, prey often combined themselves.
“Improved feeding efficiency with group predators like stentters selects multicellularity of the prey,” Dr. Ratcliffe said. “If you're a single cell, you're dinner. But if you can form a large group of cells, now you're too big to eat.”
New discoveries highlight how physical forces affect biological evolution.
“We're always thinking about genes and chemicals, but there's also a strong foundation in physics in the development of multicellular lifespan,” said Dr. Shekhar. “Even things like water flow can have an impact on evolution.”
