Ecological immunology of a tapeworms' interaction with its two consecutive hosts.

Host-parasite interactions in parasites with complex life cycles have recently gained much interest. Here, we take an evolutionary ecologist's perspective and analyse the immunological interaction of such a parasite, the model tapeworm Schistocephalus solidus, with its two intermediate hosts, a cyclopoid copepod and the three-spined stickleback. We will be focussing especially on the parallel links between the different phases during an infection in the different hosts; the immunological interactions between host(s) and parasite; and their impact on parasite establishment, growth, host manipulation and parasite virulence in the next host in the cycle. We propose to extend the 'extended phenotype' concept and not only include the ultimate but also the proximate, physiological causes. In particular, parasite-induced host manipulation is suggested to be caused by the interactions of the parasite with the hosts' immune systems.