Summary of gene loss and dN/dS ratios of the Loss and the Retained groups in the Prochlorococcus phylogeny.

Time: LCA is the root of the tree, where is also the last common ancestor of Prochlorococcus and Synechococcus; Branch labels are same as those in Figure 3.Lost: are genes that are missing in all the 12 extant Prochlorococcus genomes.Retained: are genes that are present in all the extant Prochlorococcus genomes.P-value: P-values of Student's t tests. The null hypothesis is: the Lost group has the same mean as the Retained group