Genetic differentiation in<i>Mytilus galloprovincialis</i>Lmk. throughout the world

Abstract

Abstract The mussel Mytilus galloprovincialis Lmk. has been recognized in disjunct geographic areas such as the European shore, the Pacific coasts of Asia and North America and in South Africa and Australasia. This mussel form is considered genetically fairly homogeneous within each geographic area, and the evolutionary relationships among disjunct populations are unclear. European Mytilus galloprovincialis populations from a total of 54 sampling places were examined for 3 allozyme polymorphisms (AP, Odh and Pgi) from published data. Cluster analyses show that all studied European M. galloprovincialis populations split in 2 geographically delimited clusters: Mediterranean and Atlantic. These two sets of populations are geographically separated by the Almería-Oran oceanographic barrier and the degree of genetic differentiation within each group seems to be limited. Mytilus galloprovincialis representative populations from world-wide disjunct geographic areas were analyzed for 5 allozyme loci (AP, Lap, Mpi, Odh and Pgi) from published data. Ordination and cluster analyses reveal three groups: a cluster includes the Mediterranean and the Asian and North American Pacific populations, another the European Atlantic populations, whereas the Australasian samples do not constitute a well defined cluster. Several hypotheses are advanced in order to explain this pattern of macro-geographical genetic differentiation.