Speciation by hybridization in Heliconius butterflies

Two into three does go Speciation is generally considered to result from the splitting of a single lineage into two, but recent research suggests that hybridization, where two ancestral taxa give rise to a third species by hybridization without a change in chromosome number, is a much more important motor for the origin of species than was realized. The phenomenon is still considered rare, but new examples are emerging. The latest is in the tropical butterfly Heliconius heurippa, known to have a hybrid genome, and which looks like a cross between two other species, H. cydno and H. melpomene. Further, it is shown by experiment that a hybrid trait directly causes reproductive isolation. Breeding experiments were used to recreate the intermediate wing coloration of H. heurippa and to show that its distinctive patterning reproductively isolates it from the parent species.