title: Hybridization of an invasive shrub affects tolerance and resistance to defoliation by a biological control agent.
abstract: Evolution has contributed to the successful invasion of exotic plant species in their introduced ranges, but how evolution affects particular control strategies is still under evaluation. For instance, classical biological control, a common strategy involving the utilization of highly specific natural enemies to control exotic pests, may be negatively affected by host hybridization because of shifts in plant traits, such as root allocation or chemical constituents. We investigated introgression between two parent species of the invasive shrub tamarisk (Tamarix spp.) in the western United States, and how differences in plant traits affect interactions with a biological control agent. Introgression varied strongly with latitude of origin and was highly correlated with plant performance. Increased levels of T. ramosissima introgression resulted in both higher investment in roots and tolerance to defoliation and less resistance to insect attack. Because tamarisk hybridization occurs predictably on the western U.S. landscape, managers may be able to exploit this information to maximize control efforts. Genetic differentiation in plant traits in this system underpins the importance of plant hybridization and may explain why some biological control releases are more successful than others.
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University Fort Collins, CO, USA ; Oregon Department of Forestry, Private Forests Division Salem, OR, USA.
authors.forename: Wyatt I
authors.initials: WI
authors.lastname: Williams
authors.affiliation: U.S. Geological Survey, Fort Collins Science Center Fort Collins, CO, USA.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Friedman
authors.affiliation: USDA, Agricultural Research Service Sidney, MT, USA.
authors.forename: John F
authors.initials: JF
authors.lastname: Gaskin
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University Fort Collins, CO, USA.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Norton
keywords: Tamarix sp.; biological control; hybridization; latitudinal clines; rapid evolution; resistance; tolerance