Fig. (3) Effect of migration rate among different hosts in the fraction of generalist viruses that can be maintained in the population. Migration rate increases from left to right. Increasing migration rate among different cell types favors generalist genotypes, whereas a reduced migration rate would favor viral genotypes specialized on each host. In the absence of migration, specialist viruses (black bars) dominate the population. Frequency of generalist viruses (red bars) increases with migration rate.