Fig. 3. The evolutionary consequences of hosts migrations for Complex Life Cycle parasites (CLP) local adaptations.

Migration rates often vary among the different hosts of a CLP. The migration rate of a CLP is expected to be most similar to that of its most mobile host—in this case the definitive host. Immigration of mobile hosts into a population can supply novel parasite genotypes, promoting parasite LA to the less-mobile host (which experience movement restriction at smaller scales. In snail populations, finer grain movement restriction may foster tighter genetic local adaptations as one snail subpopulation is likely to be exposed to a unique Ov local strain (in the figure, eggs from one particular color only encounter snails from one particular color). Fish are likely to be exposed to several Ov strains as they can navigate entire wetlands or watersheds (fish from one colour can encounter a limited number of cercariae of different colors). Human hosts are sharing fish and parasite from different wetlands, watersheds and even regions which contributes to parasite genotype mixing and fosters exposure to a greater diversity of parasite lineages hence minimizing tight local co-adaptations. *AH = Alternate Hosts.