Genetic variation in parasitoid resistance in natural populations of <i>Drosophila melanogaster</i>

The focus of my thesis is the variation in immunological resistance against parasitic wasps, that evolved in natural populations of the fruit fly Drosophila melanogaster. These parasitoids lay their egg in Drosophila larva and the larva can only survive by successfully encapsulating this egg. I showed that field lines differ substantially, both in encapsulation success and in genotypic variation in putative immunity genes. This led to the hypothesis that the genetic architecture for fine-tuning the immune response has evolved differently among the populations of D. melanogaster. Local adaptation of the D. melanogaster populations may have followed diverse, alternative mechanisms to resist parasitoids. The mechanisms and the influence of any particular gene is highly dependent on the genetic background and of the environmental factors that led to the evolution of resistance in the different lines. In this case, the occurrence a good “team of genes”, so called co-adapted gene complexes, would be as important as the acquisition or retaining of specific single high resistance conferring gene variants. Furthermore, the diversity and composition of bacterial communities, the microbiome, differed among the D. melanogaster field lines. That the microbiomes also is an important factor is shown by the fact that antibiotic treatment of the fly significantly altered resistance to the parasitoid Asobara tabida. This thesis highlighted the dynamic evolution of innate immune responses in natural populations