, Volume 98, Issue 1, pp 51-60

Evolutionary genetics of the Mytilus edulis complex in the North Atlantic region

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Genetic relationships among Mytilus populations throughout the North Atlantic region, including the Mediterranean and the Baltic Sea, were studied using enzyme electrophoresis. Three distinct groups of populations, each of a remarkably wide distribution, can be recognised on the basis of their multilocus allelic composition: (1) M. galloprovincialis L. of the Mediterranean and western Europe; (2) a genetically distinct form of M. edulis Lmk. from both the Baltic Sea and some localities in the Canadian Maritime Provinces (here provisionally termed the “trossulus type mussel”); and (3) the traditional “Atlantic” M. edulis populations of northwestern European coasts and most of eastern North America. These groups are regarded as representing three relatively old evolutionary lineages, which all deserve separate and equal systematic status. The main part of the differentiation at most of the loci studied is accounted for by this major systematic pattern, but considerable geographical differentiation within each of the three principal groups was also detected. At single loci, different electromorphs were found to prevail in disjunct populations of M. galloprovincialis (Mediterranean/Britain) and of the trossulus-type mussel (Baltic/eastern Canada). Within the Atlantic M. edulis, a major part of the differentiation is transoceanic. At one locus (Ap), geographic differentiation appeared to be relatively independent of the systematic boundaries; the possible role of interlineage hybridisation in contact areas in regulating the pattern of geographical variation is discussed.

Communicated by T. Fenchel, Helsingør