Figure 1

Life history of C. crescentus and selection imposed during experimental evolution. (A) The life cycle of C. crescentus begins with the release of a swarmer cell (at age 0). The swarmer cell differentiates to a stalked cell and divides for the first time at age a. The second division occurs at age a + b. The interval between divisions, b, is nearly constant early in life. The time axis is drawn to scale for C. crescentus strain UJ590; (B) The reproductive output of stalked cells of strain UJ590 decreased with increasing age (grey line, left axis; average over nine independent experiments with 30 cells; data from [12]). During experimental evolution, selection was very strong early in life, and decreased with increasing age. The red line (right axis) denotes the reduction in fitness through a mutation that leads to death at a given age, as a function of age. Death before the onset of reproduction leads to a reduction of fitness by 100%.