Causes and Consequences of Size Evolution in Drosophila melanogaster

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DESCRIPTION (provided by applicant): This research investigates the genetic basis, cellular mechanisms, and developmental consequences of body and wing size evolution in a newly discovered high altitude population of Drosophila melanogaster which represents the largest known flies of this species. This trait offers the unique opportunity to relate a biologically important phenotypic difference to its underlying cellular mechanisms and to specific genes and mutations responsible for this change. The Drosophila system offers a range of advantages to study adaptive evolution at the genetic level, from population genomic data to transgenic tools. Results will increase our knowledge of the polygenicity of adaptation and the properties of causative variants (e.g. coding vs. regulatory; new mutations vs. standing genetic variation). This research integrates biological subdisciplines to reveal cell-level mechanisms (e.g. cell proliferation and somatic ploidy) responsible for phenotypic evolution. It also takes a rare look a the potential influence of adaptive evolution on developmental stability. This work will reveal how evolution has altered the function of genes involved in insulin signaling and the cell cycle without harmful consequences to the organism - findings that may ultimately prove relevant for research on cancer, diabetes, and other medical conditions. 1. Conduct a genome-wide search for genes that play a role in body size evolution. Confirm their effects and test causative mutations using transgenesis. A novel QTL mapping method will localize causative genes to the ~100kb scale. A new population genetic statistic will reveal genes within QTL intervals that show evidence of population-specific selection in the highland sample (initial outliers include insulin signaling genes). Genes identified will be functionally tested for influence on body and wing size using a newly developed transgenic approach; specific mutations will be tested in the same way. 2. Reveal cellular mechanisms underlying body size evolution. Research will test whether changes in both cell size and number may give rise to the strikingly large wings of Ethiopian D. melanogaster. Research will also confirm whether the observed enlargement of larval muscles (polynucleate cells which strongly influence adult body size) is due to increases in the number of nuclei or their ploidy. Transgenic constructs will allow the cellular influence of specific adaptive mutations to be assessed. 3. Test whether wing size evolution disrupted developmental canalization. Ethiopian inbred lines show large wings but also very high frequencies of wing vein abnormalities. The hypothesis that phenotypic evolution has destabilized a more developmentally buffered ancestral wing state will be directly tested using a mutagenesis test of genetic perturbility. Artificial selection to recapitulate wing size evolution n the lab will further probe the generality of a link between adaptation and decanalization.