Comparative allozyme genetics and range history of the European river barbel (Teleostei, Cyprinidae: Barbus barbus) in the Rhine/upper Danube contact area

Enzymes, representing 23 genetic loci, were studied in n = 320 European river barbels (Barbus barbus L. 1758) from the contact zone of the Rhine and the upper Danube. Barbel revealed the highest heterozygosity estimate (H(e) = 0.137) of 10 sympatric freshwater fishes (range H(e) = 0.017-0.106). The geographical genetic subdivision in barbel (G(ST) = 0.1690) surpassed the respective estimates in two other cyprinid species (G(ST) <= 0.1415) and in three anadromous fishes (range G(ST) = 0.0330-0.1290) from the same study area, but it fell short of the spatial genetic fragmentation of two resident salmonid species (G(ST) >= 0.2678) and of sculpins (G(ST) = 0.8489). The theoretical gene flow in the unobstructed Danube was N(e)m(DAN) = 4.98, and across the weirs in the southern Rhine N(e)m(RHE) = 1.84. The Rhine/Danube watershed exceeded any other isolation effect on the gene pool despite a low genetic distance (D(RHE/DAN) = 0.0321) among Rhenish and Danubian samples. The range history in central Europe might imply the colonization of the study area from a Danubian and from a Rhenish or a Rhodanian refuge. The concluded admixture of eastern and western barbels has produced a weakly pronounced cline of increasing allozymic affinity of Rhenish to Danubian barbels in the Southern Rhine system. Oberschwaben has served as an important colonization pathway in the phylogeographical exchange between the Danube and west Europe. The influence of stocking for fisheries on the allozymes is not known precisely, but it appears to be of minor importance.