The role of the pleiotropic genes of the majorhistocompatibility complex in evolution : the example of the three-spined stickleback.

In this thesis, I (with colleagues) brought together the role of natural and sexual selection on the evolution of the genes of the Major histocompatibility Complex (MHC). To this end, we investigated the fitness consequences of parasite infection on both males’ and females’ fitness traits in a laboratory-study (Chapter I). Then, in two independent field-study experiments, we investigated MHC based female mate choice (Chapters II and III). In the following chapter (IV) we used the knowledge acquired on MHC-related fitness traits to predict a potential speciation mechanism mediated by these immune genes and their response to being parasitized. The fifth chapter presents correlative evidence for the proposed speciation mechanism, while the next chapter (VI) reports an empirical test of it. Finally, the last chapter reports an experimental trial to test negative-frequency-dependant selection by parasites. Except for the fourth, all chapters are structured in abstract, introduction, methods, results and discussion. In cases where the chapter has already been published, the section sequence of the original article has been maintained (Chapters 1 & 4)