Figure 1. Experimental evolution with position-dependent selection.

a, Schematic illustration of the evolution experiment. Exponentially growing E. coli CLM cells²⁷ (the ‘ancestor’) were inoculated at the center of 0.25 % TB agar plate; after 24h incubation at 37°C, after the bacteria have colonized the entire plate, a 2μl cell-agar mixture was taken at a distance X away from the plate center and inoculated at the center of a fresh plate; see Methods for details. The cycle was repeated with the samples always taken after 24 hours at the same distance X as in previous cycles. b, Expansion speeds of population samples from each of the 5 selection series are shown from Lineage 1 at various evolution cycles. Experiments were repeated 3 times obtaining similar results (see text and Extended Data Fig. 2). c, The expansion speed of 300 individual clones (60 for each selection series) isolated from the population samples at the 50^th cycle. Histogram for each series is shown with the corresponding colors. The average expansion speed of the mixed population of each selection series at 50^th cycle (shown in Extended Data Fig. 1d) are shown as the dashed lines for comparison. The expansion speeds of the ancestor and 6 mutant strains isolated at the 50^th cycle (strain A, B, B’, C, D, E) are indicated on the top of the panel, which resembled the averge expansion speed of the corresponding mixed population of lineage 1.