An evaluation of Random Amplified Polymorphic DNA (RAPD) for the identification and phylogeny of freshwater snails of the genus Bulinus (Gastropoda: Planorbidae)

Abstract

The Random Amplified Polymorphic DNA (RAPD) assay was used to study genetic variation within and between 9 species of the genus Bulinus and to determine whether RAPD profiles could be used as markers for identification purposes. RAPDs were generated with 8 primers of two different sizes (10mers & 15mers) and were visualised using both polyacrylamide gel electrophoresis (PAGE) with silver staining and agarose gel electrophoresis with ethidium bromide staining. The species groups of Bulinus had few similarities in their RAPD profiles and there was interspecific variation within groups. Intrapopulation variation was observed, with all primers, for B. globosus collected from a single site in Zimbabwe. PAGE/silver staining methods visualised a greater number of RAPDs in comparison with agarose/ethidium bromide methods. Phenetic analysis indicated that distance estimates between taxa were sometimes non-additive and the phylogenetic analysis of such non-metric data is discussed. The resultant phenograms, constructed using a least squares method, were constrained almost into a polytomy with topologies often differing between data sets. It was concluded that this phenomenon was most likely attributable to large nucleotide divergences between the species groups which go beyond the phylogenetic scope of RAPD analysis. RAPD profiles, when used in conjunction with other taxonomic methods, may contribute to the identification of species of Bulinus on a regional basis, but the observed variability in a natural population suggests that a diagnostic RAPD profile for each species throughout its geographic range is unlikely.