Congruence between allozyme and RAPD data in assessing macrogeographical genetic variation in the periwinkle Littorina striata (Mollusca, Gastropoda)

The population genetic structure of the Macaronesian planktonic-developing periwinkle Littorina striata was analysed, using random amplified polymorphic DNA analysis (RAPD). Two primers, yielding six polymorphic loci, were surveyed to infer the population genetic structure of five geographically separated populations (i.e. 10-2000km). Biased and unbiased allele frequency and heterozygosity levels were estimated and were found to be highly similar. As in previous allozyme studies, our results suggest that populations of L. striata display (i) only little amounts of genetic heterogeneity and population differentiation, (ii) high levels of gene flow, between geographically separated populations and within a single population, between two distinct shell morphs (i.e. nodulose and smooth shells) and (iii) a tendency for northern populations to be less heterozygous than southern populations. The current results reveal a high congruence between allozyme and RAPD data, suggesting that geographically separated populations and different shell morphs share a common gene pool. Given the fact that our RAPD loci might be considered as neutral markers, we conclude that the previously analysed allozymes were representative for L. striata's entire genome.