Jacobaea vulgaris(Asteraceae)is a species of Eurasian origin that has become a serious non-indigenous weed in
Australia, New Zealand, and North America. We used neutral molecular markers to (1)test for genetic bottlenecks in
invasive populations and (2)to investigate the invasion pathways. It is for the first time that molecular markers were used to unravel the process of introduction in this species.
The genetic variation of 15 native populations from Europe and 16 invasive populations from Australia, New
Zealand and North America were compared using the amplified fragment length polymorphisms(AFLP’s). An analysis of molecular variance showed that a significant part(10%)of the total genetic variations between all individuals could be explained by native or invasive origin.
Significant among-population differentiation was detected only in the native range, whereas populations from the
invasive areas did not significantly differ from each other; nor did theAustralian, NewZealand and North American
regions differ within the invasive range. The result that native populations differed significantly from each other and that the amount of genetic variation, measured as the number of polymorphic bands, did not differ between the native and invasive area, strongly suggests that introductions from multiple source populations have occurred. The lack of differentiation between invasive regions suggests that either introductions may have occurred from the same native sources in all invasive regions or subsequent introductions took place from one into another invasive region and the same mix of genotypes was subsequently introduced into all invasive regions.
An assignment test showed that European populations from Ireland, the Netherlands and the United Kingdom most
resembled the invasive populations.