Abstract
We assessed the genetic variability of the S iberian spined loach C obitis melanoleuca across its unusually broad distribution that encompasses areas greatly affected by P leistocene glaciations. Due to extensive morphological variation among their populations, the taxonomic status of C . melanoleuca is complicated. It is unclear whether C . melanoleuca represents a single taxonomic unit or contains several species or subspecies. Our analyses showed low genetic variability in all populations without any phylogenetic structure. The absence of molecular distinctiveness indicates the conspecificity of all C . melanoleuca populations. Only a few common haplotypes shared by E ast A sian, Siberian and European populations were found at high frequency in the nuclear genes analysed. At the mitochondrial level, S iberian populations shared haplotypes with populations located at both extremes of the species’ range suggesting central populations as a source of current mitochondrial variability. Unimodal mismatch distributions and significant values from neutrality tests support a recent expansion of C . melanoleuca . Our time estimates suggest a postglacial colonisation of E uropean waters around 1.0 MYA, indicating that C . melanoleuca may represent the last cobitid immigrant in E urope that used the northern route across S iberia to expand its range.