The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.
This award will support a twenty-four month research fellowship by Dr. Britt Koskella to work with Dr. Angus Buckling at the University of Oxford in the UK (thirteen months) and with Dr. John Thompson at the University of California, Santa Cruz (eleven months).
It is becoming abundantly evident that coevolution between hosts and their parasites occurs in relatively short time periods and is strongly influenced by the environment in which the interaction is occurring. Although it is clear that environmental conditions influence species interactions, exactly how the process of coevolution is shaped by gene flow across a heterogeneous landscape is yet to be resolved. This project takes a novel approach to experimental coevolutionary analysis by scaling up studies of pairwise coevolution to include interactions with a third species across a complex landscape. The PI and hosts will examine a tritrophic interaction between plant populations, the plant pathogenic bacteria Pseudomonas syringae, and its associated bacteriophages. This system is ideal for establishing the scale and magnitude of coevolutionary events at a microbial level in that the spread of bacteriophage influences both the movement and population size of bacteria, and thus the impact of bacteria on the host plant. Furthermore, since each species is directly influenced by the surrounding environmental conditions and is itself acting as a changing environment for the other two interacting species they will be able to use the three-way interaction to examine the implications of landscape heterogeneity for the coevolutionary process. Through a novel combination of carefully controlled selection experiments and surveys of natural populations they will systematically examine each component of the Geographic Mosaic Theory of Coevolution, first by quantifying the extent to which bacterial motility, known to affect bacterial virulence, and corresponding phage life-history traits vary among host plant species and populations. By setting up a series of artificial coevolution experiments between P. syringae and phage in which the plant host environment is manipulated, the variation in reciprocal selection and the relative role of gene flow is being evaluated. To complement this experimental coevolution work, a survey of phage prevalence, specificity, and local adaptation across natural populations from different geographic regions and host plant species is also being performed. Few studies have empirically explored the relative importance of geographic variation for reciprocal selection during species interactions; the proposed work will therefore greatly expand our understanding of how changing environmental conditions affect host-parasite coevolution. This research will additionally provide the basis for a novel use of phage therapy in controlling pathogenic plant bacteria. Furthermore, the project's focus on pathogen movement across complex landscapes will be particularly informative in the face of large-scale, human-mediated dispersal of crop pathogens.
