Rough periwinkle polymorphism on the east coast of Yorkshire: comparison of RAPD-DNA data with morphotype

A genetic analysis of 'morphotypes' of Littorina saxatilis from two locatio ns on the north-east coast of England (Filey and Ravenscar), using randomly amplified DNA polymorphisms (RAPD) generated with a single primer, reveale d quite different patterns of variation. Thin shelled, wide-apertured (H-fo rm) animals from Ravenscar tended to cluster separately from thick shelled (M) forms, indicating genetic differentiation of these morphs. Animals of s imilar morphology (H and M) from Filey (about 30 km distant) did not displa y such an obvious pattern, and although there was still evidence of differe ntiation from discriminant analysis of RAPD data, levels of correct classif ication were reduced at Filey. This suggests that the utility of a single R APD primer for separation of such forms varies over a relatively small dist ance. L. arcana from Ravenscar, included as an outgroup, were generally wel l differentiated from L. saxatilis and were noted to exhibit less variation , a phenomenon that has been noted previously in some allozyme and RAPD ana lyses. A similar RAPD analysis undertaken on small, barnacle dwelling, broo ding forms from Peak Steel, Ravenscar revealed that animals appeared to hav e as great a tendency to cluster together on a microgeographic scale (by co llection patch) as by 'species' (L. neglecta or L. saxatilis b) although pr edominance of certain species in individual patches largely explains this. Discriminant analysis of RAPD presence/absence data did correctly place ove r 90% of barnacle dwelling animals to their respective species, and we cons ider this as evidence of separate gene pools. RAPD is taken to be a useful tool for screening genetic variation in this complex of animals on a local scale when either a pre-selected informative primer is utilised or a batter y of primers is used, but its efficacy may be reduced when a single primer is employed for screening animals from different shores.