Moderate molecular difference in phenotypically indistinguishable populations of Luciobarbus albanicus (Teleostei: Cyprinidae).

The distribution of Luciobarbus albanicus is almost completely restricted to the Ionian Freshwater Ecoregion of western Greece, and exhibits a marked north-south phylogeographic split. We examined 27 COI sequences (635 bp) from different populations in the northern (Kalamas, Louros, Arachthos) and southern (Acheloos, Trichonis, Pinios) sections of the ecoregion to see if these groups represent distinct species. Maximum Likelihood analysis recovered two well-supported clades that matched the geographic groups. However, the average K2P genetic distance between them was only 1.36%, while the distances within each group were substantially low, i.e., 0.02% for the northern and 0.07% for the southern populations. A detailed comparison of morphometric and meristic data, including the number of lateral-line scales, circumpeduncular scales, fin-ray counts, colour patterns, and lip shapes, revealed considerable overlaps, and no clear or consistent differences. Even though the mitochondrial divergence hints at some level of population structure, the lack of consistent morphological differences suggests that the northern and southern populations of L. albanicus are best considered conspecific.