Migration highways and migration barriers created by host-parasite interactions

Coevolving parasites may play a key role in host migration and population structure. Using coevolving bacteria and viruses, we test general hypotheses as to how coevolving parasites affect the success of passive host migration between habitats that can support different intensities of host-parasite interactions. First, we show that parasites aid migration from areas of intense to weak coevolutionary interactions and impede migration in the opposite direction, as a result of intraspecific apparent competition mediated via parasites. Second, when habitats show qualitative difference such that some environments support parasite persistence while others do not, different population regulation forces (either parasitism or competitive exclusion) will reduce the success of migration in both directions. Our study shows that coevolution with parasites can predictably homogenizes or isolates host populations, depending on heterogeneity of abiotic conditions, with the second scenario constitut...