Genetic characterisation of Mytilus galloprovincialis Lmk. in North West Africa using nuclear DNA markers

The genetic relationships among Mytilus galloprovincialis populations over their range in the northeastern Atlantic and the western Mediterranean were investigated using polymerase chain reaction (PCR)-amplified nuclear DNA m arkers. We used long-range polyacrylamide gel electrophoresis for character ising an intron-length polymorphism at the actin gene locus mac-1 in Mytilu s. Sharp resolution was obtained with this technique, which revealed a high level of size polymorphism. It also allowed to discriminate between M. gal loprovincialis and M. edulis. A sample of the Padstow mussel - reported to be M. galloprovincialis according to allozyme and morphological data - exhi bited allele frequencies that were rather intermediate between M. galloprov incialis and M. edulis. We compared Mytilus samples from the northwestern A frican coasts (Morocco, Western Sahara, and Mauritania) to reference M. edu lis and M. galloprovincialis samples, and to the Padstow mussel. The northw estern African Mytilus were M. galloprovincialis as formerly suggested on t he basis of morphology and geographic location. Significant differentiation was observed between M. galloprovincialis from northwestern Africa and the reference M. galloprovincialis sample from the Mediterranean Sea, but not with M. galloprovincialis from a northeastern Atlantic population, a result that is consistent with previous allozyme- and mitochondrial DNA-based rep orts of an abrupt genetic change between northeastern Atlantic/Alboran Sea and western Mediterranean M. galloprovincialis populations. Slight heterozy gote deficiencies were possibly present within each sample as usually repor ted in bivalve populations. Additional PCRs using a second pair of primers indicated that this could hardly be explained by the occurrence of 'null' a lleles that would have resulted from mis-priming during DNA amplification. (C) 1999 Elsevier Science B.V. All rights reserved.