Evolution and diversification of wing pattern elements in swallowtail butterflies (Papilionidae)

The pattern elements of a butterfly’s wings are thought to form a system of homologies, known as symmetry systems, that are assigned a formal nomenclature under a ground plan model. Thus far, studies on wing pattern homologies have largely focused on the Nymphalidae family, with a limited amount of work dedicated to understanding the ground plan of other groups, such as the Papilionidae. The first and only complete ground plan proposed for the Papilionidae was by Schwanwitsch (1943) almost eighty years ago, long before the advent of modern molecular means that can be used to test his hypotheses. While most of the elements Schwanwitsch recognized in Papilionidae do not differ from the nymphalid groundplan, he proposed two new elements unique to Papilionidae, “rubra” and “glauca”, that appear to have played a central role in their diversification. The goal of the study was to elucidate homologies among papilionid lineages by surveying photos of a wide range of species to better understand how Schwanwitsch’s elements have diverged in Papilionidae and what their relationship to the nymphalid groundplan may be. From these photos, ML ancestral state reconstruction of ground plan elements revealed that rubra becomes lost in later lineages whereas glauca is well conserved across the entire family but has diverged considerably in form.