Figure 8. Evolutionary models of Spok diversification.

See main text for a description of the models. The models assume that an ancestral Spok homolog was present in the ancestor of both P. anserina and P. comata. The Spok diversification is traced by the inner lines. Spok2 is not included because its genomic location and sequence provide little clue as to its evolutionary history with respect to the other Spok homologs. Brown boxes represent divergence among the lineages, eventually forming P. comata and P. anserina. P. pauciseta is excluded for simplicity as in all cases it would need to obtain Spok3, Spok4 and the Spok block prior to diverging from P. anserina, and then have no divergence since the species split, or the Spok block would have to be transferred between the species.