FERRIS, M. T.*; BURCH, C. L.; University of North Carolina, Chapel Hill; University of North Carolina, Chapel Hill: Host range evolution of the bacteriophage &Phi 6: Are trade-offs required?

Viral adaptation to novel hosts can alter fitness on other hosts, and this change depends on the host-specific effects that mutations exhibit. Here we show that mutants of the RNA bacteriophage &Phi 6 that allow growth on the novel host, Pseudomonas syringae pv. glycinea, are most often costly for growth on the ancestral host, P. syringae pv. phaseolicola. We isolated a random sample of mutants which allowed growth on the novel host. We measured the fitness effects of these mutations on both the novel host, as well as the ancestral host. The majority of mutations which allow growth on the novel host come with a fitness cost on the ancestral host, although the other mutations allowing growth on the novel host have no inherent cost on the ancestral host. These results suggest that while adaptation to novel host types often has a fitness cost on other host types, such a cost is not a requirement for adaptation to novel host types. These results parallel other studies which have found that adaptation to novel environments often results in fitness losses in other environments.