Phylogenetic Scopes and Divergence of Sets of Species

<div><p>(A) Phylogenetic scope comprising hypothetical species A, B, C, D, and E. Numbers are branch lengths indicating evolutionary distances (not necessarily reflecting temporal distances). The subtree connecting species B, C, and E is shown in red and has divergence 1 + 3 + 1 + 5 + 2 + 4 = 16. Applying the greedy algorithm always produces maximally divergent extensions of the original set. For example, the subsets constructed starting with B—BE (divergence 11), BCE (16), BCDE (19)—have maximum divergence among those obtainable by adding one, two, and three additional species, respectively. The series AE (12), ACE (17), ACDE (20) is optimal among all possible subsets of two, three, and four species.</p><p>(B) Phylogenetic scope comprising placental mammals that have been or are being sequenced (in red) and candidates for future sequencing (derived from [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.0010071#pgen-0010071-b017" target="_blank">17</a>]). If five groups choose the next five targets for sequencing using the greedy strategy described in the text, the following species (in blue) will be selected (in order): (1) tenrec, (2) hedgehog, (3) rock hyrax, (4) tree shrew, (5) dog-faced fruit bat (a megabat). Within the phylogenetic scope shown, this is guaranteed to be the choice of five species that maximises the total resulting divergence. These species have recently been announced amongst targets for future sequencing [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.0010071#pgen-0010071-b009" target="_blank">9</a>].</p>