Nat. Ecol. Evol. https://doi.org/gfkwp2 (2018)

Cells in the middle of a crowded colony get jostled around as they grow and divide. And they also have an evolutionary handicap: cells at the edge grow more rapidly, and their progeny enjoy the same advantage — endowing mutant clones with higher frequencies by chance. Now, Jona Kayser and colleagues have shown that crowding screens differences in evolutionary fitness, slowing down the elimination of mutations.

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Springer Nature Ltd

Kayser and colleagues tracked the evolution of model mutant cells competing with their wild-type counterparts in a colony of yeast cells (pictured), and found that the mutants were initially eliminated at a constant rate. But when the mutant subpopulation dropped below a critical size, their removal slowed down, allowing them to persist at the front longer than expected.

The team identified suppressed curvature at the leading edge as the culprit, and showed that an effective surface tension served to align the mutants with their wild-type neighbours, thereby masking the difference in fitness between the two subpopulations. They then demonstrated numerically that mechanical forces due to cellular crowding could reproduce the same effect.