Host-parasite co-evolution and co-infection of invasive parasitic Mytilicola copepods in blue mussel hosts
Parasites are ubiquitous in nature and the strong natural selection pressures they impose on their hosts are predicted to elicit rapid evolutionary adaptive responses of hosts towards their parasites, leading to antagonistic host–parasite co-evolution. While most of what we know about these processes stems from laboratory studies with a restricted set of model organisms, much less is known about host–parasite co-evolution in the wild, largely due to logistical challenges of experimental manipulations on an ecosystem scale. Biological invasions represent excellent opportunities to overcome these logistical issues and study host–parasite interactions and co-evolution in non-model species in the wild, as they can be seen as “natural experiments” in which different invasion scenarios lead to different ecological and evolutionary dynamics. This dissertation utilises the invasions of two parasitic copepods Mytilicola intestinalis and Mytilicola orientalis in the Wadden Sea to address the study of host–parasite co-evolution and co-infection in non-model species in the wild. In general, this dissertation demonstrates the value of using biological invasions to investigate host–parasite co-evolution in the wild, which is especially promising for research on non-model organisms. Future research should, however, further unravel the relative importance of phenotypic plasticity and genetic determinism for the co-evolutionary dynamics between hosts and parasites, but should also investigate the potential effects of other factors, such as, in the case of Mytilicola, the roles of the mussel microbiome and the hyperparasite Unikaryon mytilicolae.