While organisms can sometimes expand the range of environments they live in, the genetic and ecological conditions which facilitate expansion are unclear. Proposed here are two experiments which will investigate these conditions using a virus and its bacterial host, Pseudomonas syringae. Both experiments will expose the virus to new hosts, and determine two critical determinants of the likelihood that viral populations will evolve to use the new host: 1) the number of mutations that adapt the virus to these hosts, and 2) the costs these mutations have on the virus' normal host. In the first experiment, host range mutants will be isolated on a number of new hosts to determine if the similarity between the new hosts and the normal host influences the likelihood of host range expansion. In the second experiment, mutations that allow growth on a new host will be compared to mutations that further adapt the virus to this new host. This comparison will enable the investigators to determine if these two ecological scenarios differ in their likelihood of environmental range expansion.
Understanding the conditions that facilitate the expansion of an organism's environmental range has long been a fundamental question in ecology and evolutionary biology, and also has importance for addressing applied questions such as the emergence of disease in new host populations (as when SARS emerged in human populations). While theoretical studies have provided an intuitive framework to address this issue, there has been relatively little empirical work investigating factors that influence the likelihood of range expansion. This study seeks to examine some of the ecological and genetic factors that are predicted to influence the likelihood of environmental range expansion.
