Parasite host range and the evolution of host resistance

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