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Four competing Escherichia coli strains in a spatially expanding population.

To quantitatively study the dynamics of competing genotypes in a population growing into new territory (a range expansion), four strains of E. coli, differing only by a heritable fluorescent marker, were mixed and inoculated onto a nutrient-rich agar plate. Over the course of eight days, cells at the front divided and formed a dense colony. The resulting image, which can be analyzed and understood quantitatively, depicts the formation of monoclonal sectors and provides insight into the evolutionary consequences of population expansions. Weinstein et al.

Image Credit: Bryan T. Weinstein