Fig. 4

Overview of galaxy biplots. The association between allele frequency and one variable is plotted against the association between allele frequency and a second variable. The Spearman’s ρ correlation between the two variables (mean annual temperature or MAT and mean annual precipitation or MAP in this example) is shown in the lower right corner. When the two variables are correlated, genome-wide covariance is expected to occur in the direction of their association (shown with quadrant shading in light gray). The observed genome-wide distribution of allelic effects is plotted in dark gray, and the 95% prediction ellipse is plotted as a black line. Because derived alleles were coded as 1 and ancestral alleles were coded as 0, the location of any particular SNP in bivariate space represents the type of environment that the derived allele is found in higher frequency, whereas the location of the ancestral allele would be a reflection through the origin (note only derived alleles are plotted)