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 the processes of divergence and speciation of freshwater fishes of the Iberian Peninsula, 10 populations of the Iberian endemic cyprinid Chondrostoma lemmingii were studied using 26 loci encoding 19 enzymes and the complete nucleotide sequence of the mitochondrial cytochrome b gene. Nuclear and mitochondrial DNA markers showed complete congruence in assessing the genetic differentiation among the samples analysed. This congruence was supported by a Mantel test in which a significant correlation (r=0.89) between Nei's genetic distances and sequence divergence (uncorrected p distances) was obtained. Diagnostic loci, Nei's genetic distances, and FST values, as well as the percentage of sequence divergence indicate that the Duero basin population accumulates the highest level of genetic differentiation. A moderate divergence was also observed among populations of the rest of the basins. Phenetic and phylogenetic relationships support the hypothesis that the differentiation process was not only due to hydrographical basin isolation but also due to an ancient endorrheism event, previous to hydrographical configuration, that could explain the marked differentiation of the Duero basin population.