Understanding how developmental mechanisms evolve to generate novel traits in form or disease is a major challenge of contemporary biology. By exploiting the knowledge of developmental mechanisms in genetic model organisms such as the fruit fly Drosophila, this challenge can be addressed in great molecular detail. This proposal takes advantage of a newly established experimental system, the hover fly Episyrphus balteatus (Syrphidae), to understand the genetic mechanism underlying the origin of the amnioserosa tissue, which guides important morphogenetic movements in the Drosophila embryo. The amnioserosa is not conserved but combines characteristics of two distinct tissues commonly found in other insects, the amnion and the serosa. The research goal is to understand how the genetic pathways specifying the serosa and the amnion merged into a single tissue. Episyrphus is the closest relative of Drosophila known to develop distinct amniotic and serosal epithelia and therefore of key importance for understanding this transition. By studying amnion and serosa specification in this species, it is expected to better understand how mechanisms of cell fate specification and tissue formation evolve to generate major novel traits. General benefits of this project to the research community and society will result from a deeper understanding of developmental and evolutionary mechanisms, from developing and promoting new experimental systems, and from inspiring a new generation to pursue a career in science.