River basin-related genetic structuring in an endangered fish species, Chondrostoma lusitanicum, based on mtDNA sequencing and RFLP analysis

Chondrostoma lusitanicum is a Portuguese endemic cyprinid with a restricted distribution and reduced numbers in some basins, justifying its status as a threatened species. We examined genetic population structure using sample s from throughout its geographical range in Portugal, using sequencing of b cytochrome and restriction fragment length polymorphism analysis of the NA DH subunits 5 and 6. There was reduced within-population genetic variabilit y but considerable among-population differentiation, particularly marked be tween both the Mira and Arade basins in the extreme south and other populat ions. These results confirm phylogeographic relationships suggested by prev ious fragmentary allozyme studies for C. lusitanicum, and are in accordance with allozyme and mitochondrial DNA data on phylogeography of coexisting c yprinid species of the genus Leuciscus. The levels of genetic divergence re vealed by sequence and RFLP data showed strongly concordant patterns: geogr aphical genetic structuring, with the definition of three distinct groups, was observed. The high values of nucleotide divergence and pairwise sequenc e divergence of the Mira and Arade groups, when compared with all other sam ples, support a distinct taxonomic status probably at the species level. Re sults are also discussed in relation to conservation of this highly fragmen ted species, in terms of Evolutionary Significant Units and Management Unit s.