Change in the variances after the switching of the fitness condition. After evolution under the fitness condition to favor xi >0 ("on") for all the target genes i = 1, 2, ... k(= 8) as studied already, the fitness condition was switched at a certain generation to favor xi >0 for i = 1, 2, .., k/2 and xi <0 for i = k/2 + 1, .., k (i.e., the fittest gene expression pattern was given by + + + + − − −−, instead of + + + + + + ++). The switching was applied after a sufficiently large number of generations when the fittest networks are evolved (i.e., with xi >0 for the target genes). The switch initially caused a decrease in the fitness, but after a few dozens of generations, almost all networks evolved to adapt to the new fitness condition if σ > σc. The values of the parameter and the procedure for computing the variances were identical with those in the previous cases. (i) The plot of the variances of the fitness, Vg versus Vip per generation after the switching of the fitness condition. The color represented the generation number from the switching. There was a correlation between the increase in both the variances after the switch, and then, there was a proportional decrease as adaptation to the new fitness condition progressed. (b)(c) The plot of (Vg(i) and Vip(i)) over all genes i at the generation 10, 20, and 30 for (b), and 60, 80, and 120 for (c). After the switch Vg(i) and Vip(i) increased up to 30-60 generations, while the ratio Vg(i)/Vip(i)approached unity for many genes. For generations >60, the variances decreased while the proportionality between Vg(i) and Vip(i) was regained.
Kaneko BMC Evolutionary Biology 2011 11:27 doi:10.1186/1471-2148-11-27