Evolution of Macroscopic size in nascent multicellular organism

The evolution of multicellular organisms on earth is one of the most transformative events in the history of life. Despite its importance, we know little about the process by which nascent microscopic multicellular organisms overcome substantial mechanical constraints and dramatically increase their size. We experimentally study this process with the snowflake yeast model system: baker's yeast (S. cerevisiae) with a single mutation in ACE2 gene allows mother and daughter cells to remain attached via uncut chitin bonds. These yeast clusters are composed of a few hundred cells and grow to a maximum diameter of 200 microns. After a year of artificial selection for larger multicellular size, five populations of snowflake yeast surprisingly evolved to grow to a diameter of 1 mm. In this work we show how small changes at the cell level trait lead to emergent properties in the microscopic level and helped to overcome tremendous mechanical constraints on their size.