Figure 4.

Geographic Pattern of the Genomic Signatures of Positive Selection in North American Arabidopsis lyrata, and Their Relationship with Distance from Core, Mainly Depicting Recolonization Distance after the Last Glaciation Cycle.

Results are shown on the estimate of the fraction of genes with a significant McDonald-Kreitman test (F_genesposSel) (A and B), and on the rate of adaptation, α, calculated by the aMK method on non-synonymous and synonymous sites (C and D). All panels are based on outcrossing populations only (and after correcting for all factors explaining >1% of variation, except for distance from core). The locations of selfing (red circles) and mixed-mating populations (pink circles) are shown for completeness (A and C). Maps show interpolated estimates within minimum convex polygon hulls surrounding populations of the western and eastern ancestral genetic clusters in purple and blue. Triangles indicate the core areas from which recolonization began after the most recent glacial maximum. Unshaded areas within the polygon hulls are regions with no outcrossing populations. The dashed blue line indicates the maximum extent of the ice sheet during the last glacial maximum. Plots on the right show regression lines (in black) and 95% confidence intervals (gray surface) of the relationship between population estimates of positive selection and distance from core (B and D). Signatures of positive selection declined with increasing distance from the core areas.