Document: JOH-3-16-2

Invasion and subsequent biological control of St. John's Wort (Hypericum perforatum): rapid evolution of herbivore tolerance?

MARON, J.* ¹ and C.LUKE ²

University of Washington, Seattle, WA 98195 USA ¹
San Diego State University, San Diego, CA USA ²

Abstract:
Introduced species offer superb opportunities for examining how rapid evolution can influence ecological interactions. We revisited one of the most successful weed biocontrol programs ever initiated in the United States, the control of St. John's Wort (Hypericum perforatum) to determine: 1) whether plants introduced into the western U.S. that have been exposed to 54 years of biocontrol have evolved resistance or tolerance to the biocontrol beetle, Chrysolina quadrigemina and 2) whether plants introduced into the mid-west of the U.S. that have long grown free from specialist herbivores have lost resistance or tolerance to C. quadrigemina. Regardless of their history of exposure to biocontrol, plants from introduced populations were larger than were plants from native populations in Europe when grown in a greenhouse. But in laboratory feeding trails using C. quadrigemina, introduced plants exhibited lower herbivore resistance than did their native counterparts. Despite the apparent loss of resistance, in the field, plants from populations with a history of biocontrol suppression were more tolerant of herbivory by C. quadrigemina than were plants from either the native range or the herbivore-free introduced range. Genetic analysis revealed that differences in herbivore tolerance between introduced populations are unlikely to have been caused by a founder effect. Instead, results are consistent with the hypothesis that shifting selection pressure in the introduced range has led to the loss or gain of resistance/tolerance.

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This abstract is being presented at: 2:05 PM in session:
Symposium #6: Ecological Consequences of Adaptive Evolution Among Invasive Species in Terrestrial and Marine Systems.