Eutrophication of the Baltic Sea: effects of parasites on threespine stickleback populations.

Host-pathogen research highlights the importance of environmental factors in the expression of virulence in parasites and resistance in hosts. Recently increasing evidences suggest the potential role of community structures in host-pathogen coevolution. Now there is a real challenge in understanding how biotic and abiotic factors interact to shape coevolutionary dynamics.
The threespine stickleback Gasterosteus aculeatus and its parasites are becoming an established model for the study of host-parasite interactions. In Southern Finland, several stickleback populations undergo more or less pronounced environmental change due to the human-induced eutrophication of the Baltic Sea. Distrubed areas typically exhibit differences in parasite communities, with the loss of specialist and parasites with complex life-cycle. Since trophically transmitted parasite have profound effects on the fitness of their intermediate hosts, they are supposed to maintain strong selection pressures on the evolution of host immune functions. The formal research project is interested in identifying the effects of the eutrophication of the Baltic Sea on parasite communities affecting threespine stickleback populations and its consequences in host life-history.