MACROGEOGRAPHIC DIFFERENTIATION BY MTDNA RESTRICTION SITE ANALYSIS INTHE SW EUROPEAN MYTILUS-GALLOPROVINCIALIS LMK

The mussel Mytilus galloprovincialis Lmk. is distributed in Europe fro m the Mediterranean Sea to the English Channel and British Isles. Rece ntly, an abrupt change at allozyme frequencies has been pointed out be tween Atlantic and Mediterranean Iberian populations. M. galloprovinci alis samples on both sides of the allozyme discontinuity area were tak en between 1992 and 1994. Four samples were from pure populations and one from the French hybrid zone of M. galloprovincialis and M. edulis L. A pure M. edulis sample was used as the control population, Mitocho ndrial DNA (mtDNA) restriction site analysis of EcoRI enzyme was appli ed. Significant differentiation at the haplotype frequencies between A tlantic and Mediterranean M. galloprovincialis populations was found, which represented a mean variation of about 27% for the FA haplotype f requencies. This mtDNA differentiation pattern was geographically conc ordant with that for allozyme loci previously reported. Moreover, sign ificant differences at haplotype frequencies between M. galloprovincia lis from the hybrid zone and from pure Atlantic populations were unexp ectedly found, exhibiting a mean variation of about 27% for FA haploty pe, FA frequencies for M. galloprovincialis from the hybrid zone ( > 6 8%) were not intermediate between those for Atlantic pure populations (43%) and for M. edulis (<25%). Evolutionary implications of these mac rogeographic genetic differentiations are discussed.