, Volume 161, Issue 1, pp 111-121

Genetic variation across VNTR loci in central North American Taraxacum surveyed at different spatial scales

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Dandelions (Taraxacum officinale Weber(sensu lato); Asteraceae) have been introduced to NorthandSouth America with human migration from Europe. While potential sourcepopulations have both sexually and obligate asexually (agamospermous)reproducing lineages, apparently only the latter have successfully colonizedtheAmericas. The consequences of obligate agamospermy on dandelion populationgenetic diversity in North America remain little explored. Here we use fourdifferent synthetic DNA probes that reveal genetic markers at multiplevariable-number-tandem-repeat (VNTR) loci to examine patterns of geneticvariation among plants collected along three different central North Americantransects with plants (21 to 22 individuals per transect) separated by: 1) >2 m and < 60 m (short transect); 2) > 5km and < 30 km (medium transect); and 3) > 30km and < 340 km (long transect). The mean numberofVNTR markers revealed per plant was 59.3. Co-clonal individuals (proportion ofbands shared exceeding 90%) were found in each transect, with the indexof clonality (the percent of co-clonal individuals detected in a transect)ranging from 34.12% for the short transect to 18.65% for the longtransect. Co-clonal individuals were separated by up to 200 km.With redundant examples of co-clonal individuals removed, mean similarity(proportion of band sharing) of distinct genotypes within transects was 0.426,and no statistical differences in level of similarity between transects, norindication of genetic differentiation between transects, was detected (meanFst between transect levels with all individuals included =0.05). These results indicate: 1) that dandelion genetic diversity ofcolonizinglineages in central North America is moderately high and does not reflectextreme bottleneck effects shown by some colonizing species; and 2) thatdandelion seed dispersal can be very effective in maintaining similar levels ofgenetic diversity at the different scales of sampling in this study, withcertain clones maintaining numerous, widespread individuals. Evidence that VNTRmutation is detectable within dandelion clonal lineages is presented,demonstrating that “clonal families” with lines increasinglydifferentiated from one another will continually evolve, and that Muller'srachet is, in all likelihood, turning for asexual lines.