Determining Genetic Diversity of the Seagrass Halodule Wrightii Using Random Amplified Polymorphic DNA (RAPD)

The genetic diversity of two populations of the sea grass Halodule wrightii from Christmas Bay and a Flour Bluff cooling pond in Corpus Christi was determined using Random Amplified Polymorphic DNA (RAPD). H. wrightii from Florida Bay was used for comparison. H. wrightii with a high level of genetic diversity has the best chance of adapting to a recipient site after being transplanted to Galveston Bay, Texas, which has lost over 90% of its sea grass since 1956. Sea grass beds are economically important because they provide a nursery habitat for 28% of commercial fish species and 30% of blue crab and shrimp populations in Galveston Bay. Recent technological advances have made it possible to transplant large areas with sea grass using less time and money than previous methods. Isozyme analysis had shown that H. wrightii populations in Texas had low genetic diversity. RAPD is more sensitive to detecting genetic diversity than isozymes because it samples coding and noncoding sections of the genome. The number of loci amplified allows identification of individuals within a population. RAPD revealed a high level of polymorphism. An Analysis of Molecular Variance (AMOVA) showed that approximately 60% of genetic variation was found among populations indicating a heterogeneous species. UPGMA cluster analysis showed every individual except one clustered within its population. All individuals appeared to have unique genotypes. Corpus Christi clustered more closely to Florida Bay than to Christmas Bay. These results were not expected since Corpus Christi and Florida Bay are separated by 1600 km whereas Corpus Christi is only 400 km from Christmas Bay. The similar habitats of Corpus Christi and Florida Bay may be acting as a selection agent or mating time may differ between Christmas Bay and Corpus Christi thus preventing gene flow.