UNCOVERING THE EVOLUTION AND DEVELOPMENT OF A NOVEL ABDOMINAL APPENDAGE IN BLACK SCAVENGER FLIES (SEPSIDAE: DIPTERA)

Abstract

I explore the evolution and development of a novelty in sepsid flies where males have recently evolved an elaborate brush-like appendage on the fourth abdominal segment that varies in shape and size across the family. A comparative analysis showed that male sepsids pay for more ornate 4th sternite brushes by reducing their body size and extending pupal development. I then trace the evolution of the 4th sternite brush, using a phylogenomic analysis, and show that it evolved once, was lost multiple times and reacquired in at least two species. Next, I use an optimized CRISPR/Cas9 gene editing system to test the role of candidate genes in its development in two species with morphologically distinct sternite brushes: Themira biloba and Perochaeta dikowi. I find that doublesex and abdominal-A have been co-opted into the GRN underlying 4th sternite brush development in both species. In T. biloba, extradenticle and Distal-less are additionally co-opted while there was no evidence for the involvement of Distal-less in P. dikowi, suggesting that its role in the GRN was either lost in P.dikowi or gained in T.biloba. Surprisingly, I also demonstrate a potentially unique function of doublesex and Distal-less in patterning the adult abdominal epidermis in T. biloba.