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Experimental evolution of multicellularity
Edited* by Richard E. Lenski, Michigan State University, East Lansing, MI, and approved December 14, 2011 (received for review September 19, 2011)

Abstract
Multicellularity was one of the most significant innovations in the history of life, but its initial evolution remains poorly understood. Using experimental evolution, we show that key steps in this transition could have occurred quickly. We subjected the unicellular yeast Saccharomyces cerevisiae to an environment in which we expected multicellularity to be adaptive. We observed the rapid evolution of clustering genotypes that display a novel multicellular life history characterized by reproduction via multicellular propagules, a juvenile phase, and determinate growth. The multicellular clusters are uniclonal, minimizing within-cluster genetic conflicts of interest. Simple among-cell division of labor rapidly evolved. Early multicellular strains were composed of physiologically similar cells, but these subsequently evolved higher rates of programmed cell death (apoptosis), an adaptation that increases propagule production. These results show that key aspects of multicellular complexity, a subject of central importance to biology, can readily evolve from unicellular eukaryotes.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: ratcl009{at}umn.edu.
Author contributions: W.C.R., R.F.D., and M.T. designed research; W.C.R. performed research; W.C.R., R.F.D., M.B., and M.T. analyzed data; and W.C.R., R.F.D., M.B., and M.T. wrote the paper.
The authors declare no conflict of interest.
↵*This Direct Submission article had a prearranged editor.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1115323109/-/DCSupplemental.
Freely available online through the PNAS open access option.
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- Evolution