title: Genetic admixture and heterosis may enhance the invasiveness of common ragweed.
abstract: Biological invasions are often associated with multiple introductions and genetic admixture of previously isolated populations. In addition to enhanced evolutionary potential through increased genetic variation, admixed genotypes may benefit from heterosis, which could contribute to their increased performance and invasiveness. To deepen our understanding of the mechanisms and management strategies for biological invasions, we experimentally studied whether intraspecific admixture causes heterosis in common ragweed (Ambrosia artemisiifolia) by comparing the performance of crosses (F1) between populations relative to crosses within these populations for each range (native, introduced) under different ecologically relevant conditions (control, drought, competition, simulated herbivory). Performance of admixed genotypes was highly variable, ranging from strong heterotic effects to weak outbreeding depression. Moreover, heterosis was not uniformly observed among between-population crosses, but certain native population crosses showed considerable heterosis, especially under simulated herbivory. In contrast, heterosis was largely absent in crosses from the introduced range, possibly implying that these populations were already admixed and benefit little from further mixing. In conclusion, these results support the hypothesis that heterosis may contribute to biological invasions, and indicate the need to minimize new introductions of exotic species, even if they are already present in the introduced range.
authors.affiliation: Department of Botany and Biodiversity Research Centre University of British Columbia Vancouver BC Canada.
authors.forename: Min A
authors.initials: MA
authors.lastname: Hahn
authors.affiliation: Department of Botany and Biodiversity Research Centre University of British Columbia Vancouver BC Canada; Department of Biology Indiana University Bloomington IN USA.
authors.forename: Loren H
authors.initials: LH
authors.lastname: Rieseberg
keywords: Ambrosia artemisiifolia; biological invasion; common ragweed; genetic admixture; heterosis; intraspecific hybridization; outbreeding depression