Double-layered epithelial tissues as a pathway to wing evolution in insects

Though it has been a topic of debate since the days of Darwin, how insects evolved wings is an ongoing topic of investigation with many remaining questions. Insect wings are double-layered epithelial (DLE) structures. In Drosophila, wings are the only DLE tissue type found and a large suite of genes that regulate wing development has been characterized (“wing genes”). In addition to wings, other insects have a variety of external structures composed of DLE (e.g., scutellum of Hemiptera) including structures that are inferred to have been present in wingless arthropod ancestors. However, little work has been done to evaluate the expression or function of “wing genes” in other features comprised of the same tissue type. Additionally, shared expression of “wing genes” is often used to infer serial homology to wings, although this could be a gene network conserved across DLE tissues more broadly. Many different structures have been hypothesized to be serially homologous to insect wings, from pronotal lobes, to abdominal gills, to leg segments. However, much of this work relies on the underlying assumption that the expression of “wing genes” identified in Drosophila in non-wing tissues indicates shared evolutionary origin rather than a shared tissue type (DLE). Here we present evidence that wings, and other DLE tissues are similarly impacted by a gene knockdown via RNA interference in two novel species representing hemi- and holometabolous lineages (Hemiptera and Coleoptera). Additionally, we present preliminary transcriptomic data on gene expression across wing and non-wing DLE features.