Figure 4.

Evolution of sex-biased gene expression in gonads (a) and liver (b). Ancestral state reconstructions for sex-biased gene expression are shown along the species tree in gonads and liver. Pie charts indicate the number of MBGs (blue) and FBGs (red) reconstructed at nodes, numbers in blue above edges indicate gain and loss of MBGs and numbers in red below edges indicate gain and loss of FBGs. Pairwise Spearman's rank correlation coefficients for male gene expression (blue box) and female gene expression (red box) as a function of their divergence times [11] is depicted in the categories MBG (blue background), FBG (red background) and unbiased (white background) for gonads and liver. Pairwise species comparisons are plotted with two coloured symbols which refer to each species sex chromosome as depicted in figure 1 together with the regression line (black) and 95% confidence interval (grey).