Decomposition of shape variation. The total variation of Procrustes shape coordinates (Fig. 2b) was decomposed into three components: the variation between population mean shapes, the variation between sex-specific mean shapes within populations, and the pooled residual variation within sexes and within populations. The figure shows the landmark scatters with equal frequency ellipses for these three components along with the corresponding sum of squares. The variances of these components are 2.423, 0.512, and 3.681, respectively (summed over all landmarks and multiplied by 104).