Figure 1

Evolutionary networks and gene trees. Gene trees T and T' within species networks N. (a) The gene whose tree is depicted with a dashed line is transferred from the genome of species C to that of species B. (b) Species B and C exchanged the two genes whose trees are T and T'. (c) Species B is a hybrid whose two parents are species A and C; each gene in the genome of species B has an evolutionary tree that is either T or T'.