Congruence between allozyme and cytochrome b gene sequence data in assessing genetic differentiation within the Iberian endemic Chondrostoma lemmingii (Pisces : Cyprinidae)

To understand further the fragmentation of the hydrographical basins and th e processes of divergence and speciation of freshwater fishes of the Iberia n Peninsula, 10 populations of the Iberian endemic cyprinid Chondrostoma le mmingii were studied using 26 loci encoding 19 enzymes and the complete nuc leotide sequence of the mitochondrial cytochrome b gene. Nuclear and mitoch ondrial DNA markers showed complete congruence in assessing the genetic dif ferentiation among the samples analysed. This congruence was supported by a Mantel test in which a significant correlation (r=0.89) between Nei's gene tic distances and sequence divergence (uncorrected p distances) was obtaine d. Diagnostic loci, Nei's genetic distances, and F-ST values, as well as th e percentage of sequence divergence indicate that the Duero basin populatio n accumulates the highest level of genetic differentiation. A moderate dive rgence was also observed among populations of the rest of the basins. Phene tic and phylogenetic relationships support the hypothesis that the differen tiation process was not only due to hydrographical basin isolation but also due to an ancient endorrheism event, previous to hydrographical configurat ion, that could explain the marked differentiation of the Duero basin popul ation.