Conservation score (CS, blue open circles) and non-synonymous substitution rate (dN, red crosses) as a function of the degree of a gene's expression in social versus vegetative stages (a,b) or of sexual versus vegetative stages (c). (a) For D. discoideum RNA-seq reads (1,739 genes) both regressions are significant (CS, y = -0.17x + 0.68, R2 = 0.063, P < 0.0001; dN, y = 0.11x + 0.21, R2 = 0.032, P < 0.0001). (b) For D. purpureum RNA-seq reads (3,649 genes), both regressions are also significant (CS, y = -0.20x + 0.69, R2 = 0.11, P < 0.0001; dN, y = 0.14x + 0.21, R2 = 0.017, P < 0.0001). (c) Conservation score and non-synonymous substitution rate as a function of the percentage of D. discoideum ESTs expressed in the gamete stage (932 genes, including 835 and 16 genes with a gamete expression index of 0% and 100%, respectively). Both regressions are significant: CS, y = -0.0070x + 0.73, R2 = 0.0072, P < 0.01; dN, y = 0.00051x + 0.17, R2 = 0.00708, P = 0.01.