Figure 7.

Histogram of the parsimony score S_p of the presence/absence of the variable regions of size greater than 500 bp, computed for the tree shown in Figure 1. For a given dispensable region, S_p represents the number of acquisition and loss events (S_p = N_a + N_l, where N_a and N_l are the number of acquisitions and losses, respectively) required for its pattern of presence/absence on the tree in Figure 1. The colors indicate the number of acquisitions N_a, while the number of losses can be calculated as N_l = S_p -N_a. For simplicity, all segments with N_a > 1 have been collapsed in a single bar. Since an acquisition followed by a recombination event can always be explained by multiple acquisitions, events with N_a > 1 are possible intra-species recombination events.