Populationsgenetische Analyse und experimentelle Evolution der Virulenz: die Hummel Bombus terrestris und ihr trypanosomatider Parasit Crithidia bombi

Host-parasite interactions may be influenced by processes that follow the dynamics of the Red Queen hypothesis due to a cycling of virulence and resistance factors in the parasite and host, respectively. The evolution of virulence factorsmight be driven either by between-host selection or by within-host selection. However, the relative contributions of both factors to virulence evolution has not been tested empirically. Using the bumblebee (Bombus terrestris) and their intestinal parasites Crithidia bombi (Kinetoplastida: Trypanosomatidae) we will test hypotheses for the evolution of virulence factors as well as unravel their molecular basis. The Bombus / Crithidia system is well established in the field of evolutionary ecology. Besides that, there are useful molecular tools available, that will enhance the molecular dissection of this host-parasite system. We will study natural populations to reveal the popualtion structure of host and parasite in different populations. Isolates from these populations will be used to determine the naturally occuring levels of virulence in relation to the host population structure. These data will define the parameter space that is tested empirically in an experimental evolution approach. We will conduct serial passage experiments to study the evolution of virulence depending on different factors of the host population structure (between-host selection). Furthermore, we will study within-host selection by a multiple infection approach. Finally, for both, between-host and within-host selection experiments we will study virulence effects not only in bioassays, but also at the molecular level. Here we will analyse differential gene expression of the parasite to deepen our understanding of the evolutionary dynamics of virulence genes.