Evidence for Balancing Selection at Immunity Genes in Drosophila

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The goal of this project ist o gain insights into the evolution of genes involved in the innate immunity response to parasite infection. We utilize next-generation sequence data from an ancestral (African) and a derived (European) population to detect evidence for balancing selection along the genome of Drosophila melanogaster. Balancing selection is an important biological force for maintaining advantageous genetic variation in populations. However, being mediated by diverse population genetic causes, such as genetic mechanisms (e.g. heterozygote advantage), population structure and/or complex temporal population processes, this form of selection is rather hard to study. Hence, its prevalence, patterns and targets in the genomes of most species are largely unknown. In coevolutionary host-parasite systems, it may occur on very different time scales, from very recent selective episodes to long-term processes causing trans-species polymorphism. We use specific population genetics methods to identify the target genes of balancing selection, searching for genomic signatures indicating balancing selection on short to very long evolutionary time scales. Then we analyze the immunity genes that show the strongest evidence for balancing selection to study the underlying mechanisms of this type of selection.