Geographic distance and genetic variation in Myriophyllum spicatum investigated by random amplified polymorphic (RAPD) markers

Myriophyllum spicatum, Eurasian watermilfoil, is an invasive species that has spread throughout the United States by fragments and seeds from waterfowl and boats. This species, originally from Eurasia, was introduced into North America possibly as early as the late 1800s. The number of introductions has not been established. In this study Random Amplified Polymorphic DNA (RAPD) marker variation in DNA extracted from seed-grown and plant fragments was analyzed to determine genetic diversity of plant samples from states within the United States, and countries in Asia and Europe. Four measures of genetic diversity were used: the percentage of polymorphic band fragments, Nei's diversity measure, and Nei's genetic distance and mean character difference as a distance measure. Dendrograms were created using the unweighted pair group method with arithmetic mean (UPGMA) and neighbor joining algorithms.; Geographic distance played an important role in differentiating the populations of Myriophyllum spicatum. The percentage of polymorphic fragments increased with geographic distance. The average percentage of polymorphic fragments in a single population (state or country) was 33.9 % +/− 15.2 %. This increased to 94.3% +/− 4.3% when the samples were grouped into the United States, Europe and Asia. Most of the genetic variation was between individual states (H_S) in the United States and countries in Europe and Asia. Individual states and countries formed distinct groups in the dendrograms. The European and Asian samples were genetically distinct from the United States samples. With the exception of New York State all the individual states in the United States formed discrete genetic units. Two genotypes were found in the samples from Minnesota, Wisconsin and the District of Columbia. New York State had the most genetic diversity. In New York State lakes the seed-grown fragments were clearly different from plant fragments. Geographically close lakes could not be separated by the distance measures. Only the most geographically distant lake, Lake George, formed a distinct unit. Myriophyllum spicatum 's hexaploid genome and clonal propagation maintained high polymorphism in its DNA when it invaded the United States. There are multiple genotypes and unique populations of Eurasian watermilfoil, possibly resulting from separate introductions and genetic drift.