Genome-wide relaxation of selection and the evolution of the island syndrome in Orkney voles

Sample distribution and comparison of d_N/d_S ratios. (A) Sample locations of the common vole M. arvalis in western Europe and Scotland. Continental samples are marked with green; Orkney samples, with brown. The distribution range of M. arvalis is marked with light green. Note that the species is absent from the British Isles except for Orkney. (B) For each gene, the d_N/d_S ratio of continental voles was plotted against the ratio of Orkney voles. There were more genes with higher ratio in Orkney than in the continent. The dashed line marks an equal d_N/d_S in both groups. The density of the points is marked with colors. (C) Distribution of d_N/d_S ratios of Orkney voles versus continental voles. (D) For the genes with |Δ d_N/d_S| > 0 between Orkney and continental voles, values were overall biased toward a higher d_N/d_S ratio in Orkney voles.