Clinal genetic variation and isolation by distance in the European eel Anguilla anguilla (L.)

The genetic variability and structure of the European eel (Anguilla anguilla L.) in populations throughout Europe was reassessed using 15 allozymic loci, seven of which were polymorphic. Seven sites were sampled on a latitudinal gradient across the natural continental range, extending from southern France to southern Norway. Heterozygosity (He = 0.05) and level of polymorphism (P = 0.43) were comparable to other marine fish. Populations were poorly differentiated (GST = 0.014, FST = 0.002), which is not surprising considering the high dispersal capability of the European eel. However, a significant geographical cline was detected at two alleles (IDh-1*100 and GPI-1*110), andgenetie distances (DCE) were concordant with geographical coastal distances. Mantel tests, pairwise FST's and multidimensional scaling analyses identify three distinct groups: Northern Europe, Western Europe and the Mediterranean Sea. We propose that the clinal genetic structure in the European eel may be due to (1) isolation by distance (as recently detected with microsatellites), (2) temporal reproductive separation, (3) post-larval selective forces, (4) contact between formerly separated groups or (5) some combination thereof.