Colin M .Orians DEB-9981568 & Robert S. Fritz DEB 9981406 Tufts University Vassar College
Collaborative Research RUI: Introgression of Plant Resistance Traits: Selection on Hybrid Willows by an Herbivorous Slug
Orians and Fritz will study the importance of introgression in the evolution of adaptations. They will test the hypothesis that adaptive plant resistance traits can be favored among hybrid willow genotypes due to selection by a herbivorous slug. The system is a hybridizing pair of willow species that have broadly sympatric ranges, currently hydridize throughout their zone of overlap and appear to have undergone past introgression. The PI's will make F2 progeny from pure parents of each willow species and then subject some of these progeny to herbivory by the introduced slug, A. fasciatus. Preliminary evidence suggests that slug herbivory and mortaility of seedlings is related to plant chemistry. The first experiment will test if slug herbivory causes selection favoring F2 phenotypes with higher concentrations of phenolic glycosides. Experiment two will involve determination of the chemical basis of selective slug feeding among F2 progeny compared to parentals. For Experiment 3, the PI's will measure the resistance of selected and control F2 progenies to two other major willow phytophages, Japanese beetles and willow leaf rust. This will determine if there are ecological costs of selection for higher resistance to slugs in F2's ,or, if resistance to slugs is synergistic or independent of resistance to these other species. Experiment 4 will include two generations of backcrossing and selection by slugs to determine if phenolic glycoside traits persist in backcrosses and improve the fitness of some genotypes relative to non-selected backcrosses to the willow S. eriocephala. This experiment will directly test the Introgression model, and will permit tests of allocational and ecological costs among introgressed plants with different chemical defenses.
