O’DONNELL, Brigid; University of Connecticut, Storrs: The development and evolution of abdominal gills in mayflies

Insects have highly diversified appendages, including mouthparts, antennae, wings and legs; this diversification no doubt played a role in the evolutionary success of the insects. Mayflies have highly diversified abdominal gills as aquatic nymphs, exhibiting the greatest variation in abdominal appendages in all of insects. What developmentally underlies this great diversity of mayfly gill morphology? I am investigating the proximate causes of this diversity with a combined morphological and molecular study of gill development in three focal species: Centroptilum triangulifer has single branched, lamellate gill plates, Ephoron leukon has long, bifurcate gills with many setae, and Caenis simulans has bifurcate gills with the dorsal branch modified into a hardened opercula; both E. leukon and C. simulans also exhibit differentiation of gill morphology along the abdomen. Using SEM imaging, I am describing the morphological progression of gill development. Gills appear after the first nymphal molt, and are uniramous, thread-like, and lack morphological modification in species examined to date. With subsequent molts, gills gain characteristic features: extra branches, setae, changes in gross shape and sclerotization. From a molecular standpoint, I am investigating the early patterning of gills, gill branching events and intra-individual variation in gill morphology by characterizing the expression patterns of wingless and distal-less, both used in the axial patterning of appendages, and Ultrabithorax, implicated in anterior to posterior differentiation of appendages. Investigating the development of gills in mayflies offers exciting promise for clues as to whether these structures are homologous to legs or wings in other insects.