Cellular Packing, Mechanical Stress and the Evolution of Multicellularity

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Jacobeen, Shane
Brandys, Colin G.
Graba, Elyes C.
Pentz, Jennifer T.
Ratcliff, William C.
Yunker, Peter J.
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The evolution of multicellularity set the stage for sustained increases in organismal complexity. However, a fundamental aspect of this transition remains largely unknown: how do simple clusters of cells evolve increased size when confronted by forces capable of breaking intracellular bonds? Here we show that multicellular snowflake yeast clusters fracture due to crowding-induced mechanical stress. Over seven weeks (~291 generations) of daily selection for large size, snowflake clusters evolve to increase their radius 1.7-fold by reducing the accumulation of internal stress. During this period, cells within the clusters evolve to be more elongated, concomitant with a decrease in the cellular volume fraction of the clusters. The associated increase in free space reduces the internal stress caused by cellular growth, thus delaying fracture and increasing cluster size. This work demonstrates how readily natural selection finds simple, physical solutions to spatial constraints that limit the evolution of group size—a fundamental step in the evolution of multicellularity.
Georgia Institute of Technology. College of Sciences
Georgia Institute of Technology. Institute for Materials
Georgia Institute of Technology. Parker H. Petit Institute for Bioengineering and Bioscience
Georgia Institute of Technology. School of Materials Science and Engineering
Georgia Institute of Technology. School of Physics
American Physical Society
Exxon Mobil Corporation
National Science Foundation (U.S.)
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09:46 minutes
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