Epistatic interactions are prevalent in Drosophila 3UTR evolution. Ying Zhen, Peter Andolfatto. Ecology and Evolutionary Biology, Princeton University, Princeton, NJ.

   It has been shown that a large fraction of noncoding DNA in Drosophila is evolutionarily constrained and may be target of substantial adaptive evolution. With the available population polymorphism data in Drosophila melanogaster and D. simulans, we identify candidate 3UTRs showing strongest evidence of recurrent adaptive evolution. In a panel of five these candidate 3UTRs, we use GAL4-driven Luciferase-3UTR reporter assays in D. melanogaster transgenic lines to test the effects of 3UTR divergence on the levels of gene expression divergence between species, controlling for chromosome location and genomic context. In addition, chimeric 3UTRs are used to understand how substitutions interact and contribute to changes in gene expression. Our results indicate that in all of our five 3UTR candidates sequence divergence is associated with differences in gene expression and that expression divergence is the result of complex interactions among substitutions, and epistatic interactions are prevalent. We also find that the interaction between substitutions and the final expression difference output is sex and tissue specific.