Population genetic analysis of two species of non-indigenous riparian weeds in northeast England in the context of their spatial ecology
The population genetic structure of two species of invasive non-indigenous riparian weeds in the Northeast of England was investigated using microsatellite markers. Heracleum mantegazzianum and Impatiens glandulifera were introduced into the UK from Asia. The first records of the species in the Tees, Tyne and Wear catchment areas were in 1944 and 1892 respectively. Both species have spread rapidly, and are present over a wide area of the catchments. The pattern of genetic variation was investigated in order to determine the importance of anthropogenic introduction, and life-history and dispersal strategies to the distribution of the species. Twelve populations of each species were sampled from the Tees, Tyne and Wear catchments as well as an independent population for comparison. Genomic libraries were constructed and screened for dinucleotide repeat microsatellite loci. Four polymorphic loci of H. mantegazzianum and three of I. glandulfera were identified, and each species was also screened for variation using one universal chloroplast microsatellite locus. A large amount of variation was found in both species as the loci of H. mantegazzianum had between nine and twenty alleles and those of I. glandulifera between eight and sixteen alleles. Results revealed greater overall variation between populations from different catchments than those in the same catchment. Within a catchment, there was evidence of isolation by distance for both species in one out of two catchments examined. Populations of I. glandulifera showed greater temporal variation and there was more variation both overall and within a catchment in this species. This is likely to be due to the larger number of individuals present, and the wider distribution of this species. Low levels of chloroplast variation were found in both species. This may reflect a lack of variation in the material introduced into the UK.