title: Propagule pressure, genetic structure, and geographic origins of Chondrilla juncea (Asteraceae): an apomictic invader on three continents.
abstract: OBJECTIVE
  Assessing propagule pressure and geographic origins of invasive species provides insight into the invasion process. Rush skeletonweed (Chondrilla juncea; Asteraceae) is an apomictic, perennial plant that is invasive in Australia, South America (Argentina), and North America (Canada and the United States). This study comprehensively compares propagule pressure and geographic structure of genotypes to improve our understanding of a clonal invasion and enhance management strategies. •
  
  
  METHODS
  We analyzed 1056 native range plants from Eurasia and 1156 plants from three invaded continents using amplified fragment length polymorphism (AFLP) techniques. We used measures of diversity (Simpson's D) and evenness (E), analysis of molecular variance, and Mantel tests to compare invasions, and genotype similarity to determine origins of invasive genotypes. •
  
  
  RESULTS
  We found 682 unique genotypes in the native range, but only 13 in the invaded regions. Each invaded region contained distinct AFLP genotypes, suggesting independent introduction events, probably with different geographic origins. Relatively low propagule pressure was associated with each introduction around the globe, but levels of among-population variation differed. We found exact AFLP genotype matches between the native and invaded ranges for five of the 13 invasive genotypes. •
  
  
  CONCLUSIONS
  Invasion dynamics can vary across invaded ranges within a species. Intensive sampling for molecular analyses can provide insight for understanding intraspecific invasion dynamics, which can hold significance for the management of plant species, especially by finding origins and distributions of invasive genotypes for classical biological control efforts.
authors.affiliation: USDA Agricultural Research Service, Northern Plains Agricultural Research Laboratory, 1500 N. Central Ave., Sidney, Montana 59270, USA.
authors.forename: John F
authors.initials: JF
authors.lastname: Gaskin
authors.forename: Mark
authors.initials: M
authors.lastname: Schwarzländer
authors.forename: C Lynn
authors.initials: CL
authors.lastname: Kinter
authors.forename: James F
authors.initials: JF
authors.lastname: Smith
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Novak
mesh_terms: D054458:Amplified Fragment Length Polymorphism Analysis; D019659:Asteraceae / Q000235:genetics*; D001315:Australia; D035264:Flowers / Q000235:genetics; D005819:Genetic Markers; D040342:Genetic Structures; D014644:Genetic Variation; D005828:Genetics, Population; D005838:Genotype; D005843:Geography; D006239:Haplotypes; D058865:Introduced Species; D009656:North America; D011157:Population Dynamics; D017422:Sequence Analysis, DNA; D013020:South America
chemical_list: D005819:Genetic Markers
keywords: AFLPs; Asteraceae; Chondrilla juncea; biological control; invasive; origins; propagule pressure; rush skeletonweed; weed