Macrogeographic differentiation by mtDNA restriction site analysis in the S.W. European Mytilus galloprovincialis Lmk

Abstract

The mussel Mytilus galloprovincialis Lmk. is distributed in Europe from the Mediterranean Sea to the English Channel and British Isles. Recently, an abrupt change at allozyme frequencies has been pointed out between Atlantic and Mediterranean Iberian populations. M. galloprovincialis samples on both sides of the allozyme discontinuity area were taken 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. Mitochondrial DNA (mtDNA) restriction site analysis of EcoRI enzyme was applied. Significant differentiation at the haplotype frequencies between Atlantic and Mediterranean M. galloprovincialis populations was found, which represented a mean variation of about 27% for the FA haplotype frequencies. This mtDNA differentiation pattern was geographically concordant with that for allozyme loci previously reported. Moreover, significant differences at haplotype frequencies between M. galloprovincialis from the hybrid zone and from pure Atlantic populations were unexpectedly found, exhibiting a mean variation of about 27% for FA haplotype. FA frequencies for M. galloprovincialis from the hybrid zone (> 68%) were not intermediate between those for Atlantic pure populations (43%) and for M. edulis (< 25%). Evolutionary implications of these macrogeographic genetic differentiations are discussed.