After 30 days, the algae in the center were still single-celled. But when the scientists looked at the algae under a microscope in the thickening rings, they found larger clumps of cells. The largest were clusters of hundreds of cells. But what interested Simpson most were mobile clusters of four to 16 cells, arranged so that their flagella were all on the outside. The clusters moved by coordinating the movement of their flagella. The ones at the back of the cluster were stationary, while those at the front wiggled.
Comparing the speed of these clusters to the single cells in the middle revealed something interesting. “They all swim at the same speed,” Simpson said. By working together as a group, the algae were able to maintain their mobility. “That was really exciting,” he said. “Using a rough mathematical framework, we were able to make some predictions. And the fact that we can actually see it empirically means that there’s something to this idea.”
Interestingly, when the scientists took these little clusters out of the high-viscosity gel and put them back in a low-viscosity gel, the cells stuck together. In fact, they stayed that way for about 100 generations, as long as the scientists kept watching. Simpson says the changes they had made to survive in the high viscosity were hard to reverse. It may not be a short-term change, but rather a move toward evolution.
illustration
Caption: In a gel as viscous as the ancient ocean, algae cells began to work together. They clumped together and coordinated the movements of their tail-like flagella to swim faster. When the viscosity was restored to normal, they stayed together.
Source: Andrea Halling
Modern birds are not early animals, but the idea that these physical pressures would have forced single-celled organisms into an alternative way of life that would be difficult to reverse is very compelling, Simpson said. He thinks that if scientists explore the idea that viscosity governs existence when organisms are very small, we might learn something about the conditions that might have led to the explosion of life on a grand scale.
Cellular perspective
We are large creatures, so we don’t think much about the thickness of the fluid around us. It’s not part of our everyday experience, and we are so large that viscosity doesn’t affect us much. The ability to move relatively easily is something we take for granted. Ever since Simpson first realized that such a limitation of movement could be a monumental obstacle to microscopic life, he hasn’t been able to stop thinking about it. Viscosity may have been quite important in the origin of complex life.
“[This perspective] “This allows us to think about the deep time history of this transition,” Simpson said, “and what happened in Earth history when all of the obligately complex multicellular groups evolved, which we think were relatively close together.”
Other researchers find Simpson’s idea quite novel. Before Simpson, no one seemed to have thought much about the physical experiences of organisms in the ocean during Snowball Earth. Nick Butterfield A PhD in early life evolution at Cambridge University. But he cheerfully noted that “Karl’s ideas are peripheral” because most theories about the influence of snowball earth on the evolution of multicellular animals, plants and algae focus on how oxygen levels inferred from isotope levels in rocks might have tipped the scales in some way.
