River basin-related genetic structuring in an endangered fish species, Chondrostoma lusitanicum, based on mtDNA...

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 samples from throughout its geographical range in Portugal, using sequencing of b cytochrome and restriction fragment length polymorphism analysis of the NADH subunits 5 and 6. There was reduced within-population genetic variability but considerable among-population differentiation, particularly marked between both the Mira and Arade basins in the extreme south and other populations. These results confirm phylogeographic relationships suggested by previous fragmentary allozyme studies for C. lusitanicum, and are in accordance with allozyme and mitochondrial DNA data on phylogeography of coexisting cyprinid species of the genus Leuciscus. The levels of genetic divergence revealed by sequence and RFLP data showed strongly concordant patterns: geographical genetic structuring, with the definition of three distinct groups, was observed. The high values of nucleotide divergence and pairwise sequence divergence of the Mira and Arade groups, when compared with all other samples, support a distinct taxonomic status probably at the species level. Results are also discussed in relation to conservation of this highly fragmented species, in terms of Evolutionary Significant Units and Management Units.