Figure 2.

Reticulated patterns. Different processes can result in reticulated patterns of evolution. The left panel shows an idealized, fully bifurcating species tree representing the evolutionary relationships among species A to I. Three types of events are marked with circles, ellipses, and arrows: (1) an HGT event from species A to H; (2) a hybridation event between species D and F, originating the hybrid species E; and (3) a hybridization between species H and I resulting in introgression from species H into the genome of species I. The central panels shows gene phylogenies presenting incongruences or altered branch patterns resulting from these events: (1) a gene from species H clusters with homologs from the phylogenetically distant species A and B; (2) conflicting patterns found among gene trees in D and E form a clade to the exclusion of F; in others E and F form a clade to the exclusion of D; and (3) genes from the introgressed regions in species I show shorter distances with homologs of species H (right), as compared with nonintrogressed regions (left). The right panel shows a reticulated tree for the same species, here including information on the past reticulation events.