Tempo of degeneration in Microbotryum fungi. (A) Frequency of optimal codons N^optimal/(N^optimal + N^nonoptimal) as a function of time since recombination suppression (in Million years, My). Note that the statistical analyses were performed on the odds of optimal codons (N^optimal/N^nonoptimal) and not the frequency as plotted here. (B) Nonsynonymous over synonymous divergence (d_N/d_S) between alleles on the two mating-type chromosomes, as a proxy of the strength of purifying selection, as a function of time since recombination suppression (in My). (C) Accumulation of nonsynonymous changes accumulation (d_N) between alleles on the two mating-type chromosomes as a function of time since recombination suppression (in My). In all panels, the dots represent the data. Predictions from the models are show as red lines and the 95% confidence intervals of the prediction as grey areas.