Parasite host range and the evolution of host resistance

Parasite host range plays a pivotal role in the evolution and ecology of hosts
and the emergence of infectious disease. Although the factors that promote
host range and the epidemiological consequences of variation in host range
are relatively well characterized, the effect of parasite host range on host
resistance evolution is less well understood. In this study, we tested the
impact of parasite host range on host resistance evolution. To do so, we used
the host bacterium Pseudomonas fluorescens SBW25 and a diverse suite of coevolved
viral parasites (lytic bacteriophage Φ2) with variable host ranges
(defined here as the number of host genotypes that can be infected) as our
experimental model organisms. Our results show that resistance evolution
to coevolved phages occurred at a much lower rate than to ancestral phage
(approximately 50% vs. 100%), but the host range of coevolved phages did
not influence the likelihood of resistance evolution. We also show that the
host range of both single parasites and populations of parasites does not
affect the breadth of the resulting resistance range in a na€ıve host but that
hosts that evolve resistance to single parasites are more likely to resist other
(genetically) more closely related parasites as a correlated response. These
findings have important implications for our understanding of resistance
evolution in natural populations of bacteria and viruses and other host–parasite
combinations with similar underlying infection genetics, as well as the
development of phage therapy