Funding for the research was obtained in February 2011, with coauthors R. Ford Denison and Mark Borrello, adjunct and associate professors, respectively, in the Department of Ecology, Evolution and Behavior.
Ratcliff and Travisano gave the scientific community a glimpse of their discovery at a conference last summer and have subsequently been invited to talk about it at other meetings. The PNAS article represents the first time full details about the research have been disclosed. "The article provides us with the first opportunity to show the breadth of evolutionary change that we've observed," Travisano says.
In essence, here's how the experiments worked. The two chose brewer's yeast or Saccharomyces cerevisiae, a species of yeast used since ancient times to make bread and beer, because it is abundant in nature and grows easily. They added it to a nutrient-rich culture media and allowed the cells to grow for a day in test tubes. Then they used a centrifuge to stratify the contents by weight. As the mixture settled, cell clusters landed on the bottom of the tubes faster because they are heavier. They removed the clusters, transferred them to fresh media, and grew them up again. Sixty cycles later, the clusters now hundreds of cells looked roughly like spherical snowflakes.
Analysis showed that the clusters were not just groups of random cells that adhered to each other, but related cells that remained attached following cell division. That was significant because it meant they were genetically similar, which promotes cooperation. When the clusters reached a critical size, some cells essentially committed suicide (apoptosis) to allow offspring to separate. The offspring reproduced only after they attained the size of their parents.
"A cluster alone
|Contact: Jeff Falk|
University of Minnesota