Relative ages of A. thaliana LTR retroelement lineages. (a) Box-plot showing the age distribution of Pseudoviridae full-length elements contrasted with those of the Metaviridae. The position of the median is shown as a gray bar in the box that delimits the boundaries of the lower and upper quartiles. Data points more than 1.5 times the inter-quartile range above the upper quartile or below the lower quartile are indicated by individual horizontal lines. Ages were calculated as described in Materials and methods. (b) Relative-age box-plots of Metaviridae sublineages. Permutation test p-values for the significance of the displayed age distributions are shown below each box-plot.