Comparison of genetic diversity of the invasive weed Rubus alceifolius Poir. (Rosaceae) in its native range and in areas of introduction, using amplified fragment length polymorphism (AFLP) markers

Theory predicts that colonization of new areas will be associated with popu lation bottlenecks that reduce within-population genetic diversity and incr ease genetic differentiation among populations. This should be especially t rue for weedy plant species, which are often characterized by self-compatib le breeding systems and vegetative propagation. To test this prediction, an d to evaluate alternative scenarios for the history of introduction, the ge netic diversity of Rubus alceifolius was studied with amplified fragment le ngth polymorphism (AFLP) markers in its native range in southeast Asia and in several areas where this plant has been introduced and is now a serious weed (Indian Ocean islands, Australia). In its native range, R. alceifolius showed great genetic variability within populations and among geographical ly close populations (populations sampled ranging from northern Vietnam to Java). In Madagascar, genetic variability was somewhat lower than in its na tive range, but still considerable. Each population sampled in the other In dian Ocean islands (Mayotte, La Reunion, Mauritius) was characterized by a single different genotype of R. alceifolius for the markers studied, and cl osely related to individuals from Madagascar. Queensland populations also i ncluded only a single genotype, identical to that found in Mauritius. These results suggest that R. alceifolius was first introduced into Madagascar, perhaps on multiple occasions, and that Madagascan individuals were the imm ediate source of plants that colonized other areas of introduction. Success ive nested founder events appear to have resulted in cumulative reduction i n genetic diversity. Possible explanations for the monoclonality of R. alce ifolius in many areas of introduction are discussed.