Genetic variation and population structure of the garden escaper Lupinus polyphyllus in Finland

Analysis of the amount and distribution of genetic variation can yield information about the number of introductions and history of an invasive species, which may be relevant for understanding the evolutionary potential and spread of invaders, as well as for creating best management practices for curbing them. We explored the genetic patterns and invasion history of the perennial, ornamental herb Lupinus polyphyllus Lindl. in Finland, where the species has spread rapidly during the past hundred years. Using 13 microsatellite loci, we determined the genetic variation of L. polyphyllus in 51 sites across a latitudinal gradient that reflected the invasion history of the species in this country. We found that the sampled populations were significantly genetically differentiated among sites, as indicated by the global F'(ST) value (0.19) and AMOVA results (16.7 % of total genetic variation occurred among sites), and this differentiation slightly increased with increasing geographic distance (r = 0.11, P = 0.006), indicating limited gene flow. Genetic variation of L. polyphyllus, measured as the average number of alleles per site or the average number of unshared alleles between pairs of individuals per site, was not associated with latitude. Our results suggest that the invasive populations of L. polyphyllus are genetically differentiated in Finland, but show no evidence of a loss of genetic variation during the invasion process. Overall, this pattern reflects human-mediated dispersal with multiple introductions from different sources rather than the natural spread of L. polyphyllus from a single or few sources in Finland.