Host parasite interactions in a cestode with a complex life cycle, Schistocephalus solidus
Many parasites have complex life cycles, i.e. they have to pass through several host species to reach maturity. Hence complex life cycles often consist of invertebrate and vertebrate hosts, the parasite likely varies in the machinery required for infection, exploitation and transmission of each host. Does the ability to optimally exploit one host inevitably lead to a reduced ability for the parasite to exploit another host in its life cycle? To answer this question, I analysed parasite life history traits like transmission, infection, and establishment in the model system of the tapeworm Schistocephalus solidus in relation to its two intermediate hosts, a cyclopoid copepod, and the three-spined stickleback. In this thesis, I particularly focus on interactions with the hosts' immune systems and on constraints, which are potentially shaping the evolution of virulence in parasites with complex life cycles.