Fig. 1.
Given the guide species tree (A), each species delimitation is represented by a set of flags indicating whether each of the four ancestral nodes (6, 7, 8, 9) is collapsed (0) or resolved (1). For this guide tree, there exist seven species delimitations, shown in B, where 0000 indicates all nodes are collapsed so that there is only one species, and 1111 indicates the fully resolved tree with five species. The reversible-jump algorithm allows moves between species delimitations connected in B. The probabilities of the species delimitations under the uniform Dirichlet prior with equal probabilities for each labeled history are shown in parentheses. For example, tree 1101 has prior probability 0.2 because this tree corresponds to two labeled histories, with node 9 being older or younger than node 7, respectively (node 8 is collapsed in tree 1101). The prior with equal probabilities for the rooted trees assigns probability 1/7 for each of these species delimitations.