Evolutionary genomics of the immune response against parasitoids in Drosophila

Parasites constitute a strong selective force in nature, and organisms evolve defence mechanisms to cope with them. The central questions of the thesis of Laura Salazar Jaramillo are how these mechanisms evolve and are encoded in the genome, and how they can be lost during evolution. Her research focused on an immune response called melanotic encapsulation, which is used by Drosophila fruit flies to survive attacks by parasitoid wasps that lay their eggs in the fruit fly larvae. Drosophila species and populations vary largely in how successful they are in surviving parasitoid attack, with some species completely lacking the ability to resist. Salazar’s research indicates that this defence mechanism evolved recently in a subgroup of Drosophila species that contains D. melanogaster. Its evolution is associated with the acquisition of new genes and a new type of blood cells. Comparisons among Drosophila species and populations of D. melanogaster revealed considerable variation in the expression of some of these genes. Inside the group of species able to resist, the encapsulation ability was lost in the endemic island species D. sechellia that specialized on a fruit that can be toxic to other insects. Salazar’s experiments and field study showed a reduced risk of parasitoid attack in these fruits. In conclusion, by combining evolutionary genomics with ecological information, she characterized the components that enable some Drosophila species to mount a successful immune response to a lethal parasitoid infection, how this response is modulated among populations of one species and how it was lost in a particular ecological setting.

Dissertation: http://irs.ub.rug.nl/ppn/386029377