Copy number variation and the limits of natural seleciton in Drosophila yakuba and Drosophila simulans. Rebekah L. Rogers¹, Julie M. Cridland², Ling Shao¹, Kevin R Thornton¹. 1) Ecology and Evolutionary Biology, University of California, Irvine, CA; 2) Department Of Evolution and Ecology, University of California, Davis, CA.

   Gene duplications are key contributors to adaptive evolution and mophological diversity. We have used paired-end Illumina sequencing to identify segregating duplications in populations of Drosophila yakuba and Drosophila simulans. We find evidence for natural selection favoring duplications in D. simulans especially those that fall on the X chromosome. Furthermore, we see overrepresentation of duplicate genes involved in rapid evolutionary processes such as immune defense, and evolution of chemosensory and photosensory perception, chitin cuticle formation, and chorion development. We identify large numbers of abnormal gene constructs such as chimeric genes and recruitment of formerly noncoding sequence. In addition, many tandem duplications may disrupt or silence genes, suggesting that tandem duplications can serve as forces of destruction in addition to their role in generating new genes. While we observe large numbers of segregating gene duplications in both species, the likelihood that a duplication of any single gene is present in the population is still low. Hence, evolution is likely to be severely limited by mutation with respect to duplicate genes, especially in cases where environments change rapidly or often.