Evidence for a dual origin of insect wings via cross-wiring of ancestral tergal and pleural gene regulatory networks

Scientists have long been fascinated by morphological novelties, which at times seem to spring out of the ancestral form from no pre-existing structure (or structures, i.e. a complex novel trait). With molecular biology, it is relatively straightforward to work out the genes and regulatory interactions responsible for the proper development of these structures in extant species. However, what is more important from an evolutionary perspective (and more difficult to determine) is how a developmental gene regulatory network (GRN) is first pieced-together to create a novel structure. An intriguing possibility is that two or more ancestral GRNs may become cross-wired to drive the formation of a complex novel structure that is radically different from its origin tissues. The objective of this dissertation is to better understand how pre-existing GRNs from more than one origin tissue may combine to spark the origin of a complex morphological novelty, focusing on the origin of the insect wing. This chapter will provide background knowledge on the evolutionary impact of wing origin on the insects (Section 1.2), as well as relevant information on the development and morphology of the wings and proposed origin tissues (Section 1.3). This is followed by a brief history of the wing origin debate utilizing traditional comparative morphology (Section 1.4), a review of the major components of the wing GRN in the fruit fly (Section 1.5), and finally, a discussion on what evo-devo studies have discovered regarding the origin of the wing GRN (Section 1.6).