(A) Venn diagram demonstrating the number of genes showing evidence of positive selection between four different combinations of species. As illustrated, several genes showed a significantly higher Ka value in more than one pairwise species combination. (B) The parameter α estimated for all genes and for a subset of genes encoding signal peptides. The figure contrasts estimates of the two groups of genes on chromosomes 1–13 in the two combinations of species M. graminicola and S1 (MgS1) and M. graminicola and S2 (MgS2). Although the chromosomes show a high extent of heterogeneity, the signal peptide encoding genes overall have a significantly higher extent of adaptive evolution.
