Genetic differentiation of the Iberian amphiodus Gammarus ibericus Margalef, 1951 and G. gauthieri S. Karaman, 1935, with reference to some related species in France

Populations of five related species belonging to the Gammarus pulex group from the Iberian Peninsula and southern France have been studied electrophoretically at 21 enzyme loci. Morphologically distinct forms from the same side of the Pyrenees proved to be genetically more similar than morphologically very similar forms from opposite sides of this barrier. With reference to published data, genetic differentiation between French and Iberian species was observed at the generic level. Inter-areal intraspecific genetic differentiation in Iberian species may warrant recognition of subspecies or sibling species. However, cross-breeding experiments performed did not assess levels of reproductive isolation of the forms involved. A dendrogram derived from genetic distances (D) was compared with geological and paleoclimatological evidence. Although hypotheses derived from the alternative data bases do not conflict, they give little information with regard to evolutionary rates of the loci involved