Treehopper morphology evolution: comparative body part transcriptomes of three treehopper species and two relatives

Novel morphological traits often mark the origin of major clades. Novelties move taxa into new areas of morphospace, thereby conferring new adaptive potential on a lineage. Thus,determining how novel traits originate is central to our ability to explain how morphological diversification occurs, and is a core question in evolutionary developmental biology. In arthropods and many other taxa, body wall outgrowths serve as major sources of evolutionary novelty. Developmentally, morphological novelties arise through the emergence of organ-specific gene networks. Such networks generally do not arise from scratch (i.e., de novo), but rather by elaboration or cooption of existing gene networks. Thus, comparative data make it possible to determine the evolutionary source(s) of these regulatory networks and to reconstruct the developmental changes producing novelty. By combining RNA-seq with analyses of gene function in a phylogenetic context, this project will test multiple hypotheses for the origin of a novel, highly evolvable body wall outgrowth, the treehopper helmet.We will generate a dataset including 3 biological replicates of 8 tissues from 2 developmental timepoints in 4 species (and from 1 developmental timepoint in a 5th species) [144 transcriptomes]. The species include three treehoppers from across the treehopper phylogeny (Entylia carinata, subfamily Smiliinae, Enchenopa binotata, subfamily Membracinae, and Microcentrus caryae, subfamily Stegaspidinae), the leafhopper Homalodisca vitripennis, and a hemipteran outgroup, the milkweed bug Oncopeltus fasciatus. Tissues will include pronotum, mesonotum, forewings, hind wings, ovipositor, dorsal abdominal body wall, and eye. Like wings (and the treehopper helmet), the ovipositor is an adult-specific feature that undergoes a dramatic transformation during the last nymphal instar. Its inclusion serves as a control to distinguish sets of genes required for extensive premetamorphic proliferation from those with specific patterning functions. Abdominal body wall is serially homologous to the pro- and mesonota, providing an additional test of the expectation that serial homologs without major changes in structure or function remain transcriptionally similar. Finally, because it is divergent in structure, function and developmental origin, the eye acts analogously to a taxonomic outgroup in phylogenetic trees. As hemipteran metamorphosis is gradual, we will sample tissues at both the penultimate and last nymphal stages.