GENETIC DIFFERENTIATION IN MYTILUS-GALLOPROVINCIALIS LMK. THROUGHOUT THE WORLD

The mussel Mytilus galloprovincialis Lmk. has been recognized in disju nct geographic areas such as the European shore, the Pacific coasts of Asia and North America and in South Africa and Australasia. This muss el form is considered genetically fairly homogeneous within each geogr aphic area, and the evolutionary relationships among disjunct populati ons are unclear. European Mytilus galloprovincialis populations from a total of 54 sampling places were examined for 3 allozyme polymorphism s (Ap, Odh and Pgi) from published data. Cluster analyses show that al l studied European hi. galloprovincialis populations split in 2 geogra phically delimited clusters: Mediterranean and Atlantic. These two set s of populations are geographically separated by the Almeria-Oran ocea nographic barrier and the degree of genetic differentiation within eac h group seems to be limited. Mytilus galloprovincialis representative populations from world-wide disjunct geographic areas were analyzed fo r 5 allozyme loci (Ap, Lab, Mpi, Odh and Pgi) from published data. Ord ination and cluster analyses reveal three groups: a cluster includes t he Mediterranean and the Asian and North American Pacific populations, another the European Atlantic populations, whereas the Australasian s amples do not constitute a well defined cluster. Several hypotheses ar e advanced in order to explain this pattern of macro-geographical gene tic differentiation.