Molecular and osteological verification of the taxonomic status of Phoxinus sedelnikowi (Berg, 1908) (Teleostei: Leuciscidae)

Abstract Phoxinus sedelnikowi is a Central Asian representative of the genus Phoxinus, occurring in the tributaries of Lake Zaisan at the southern foot of the Altai Mountains. Its systematic position has so far been unclear. It was considered a subspecies of Rhynchocypris czekanowskii, R. lagowskii and P. phoxinus. Here, we sequenced the cytochrome b gene and ATP-ase subunits 6 and 8 of representatives of P. sedelnikowi and two populations of P. phoxinus (including the topotypical population) and R. czekanowskii, R. lagowskii, and R. percnurus. We also performed an analysis of the shapes of the seven bones of the skull of all six forms examined and then performed a phylogenetic interpretation of the obtained results. Both P. sedelnikowi and Phoxinus sp. from the Solonovka population appeared to be separate from P. phoxinus from the topotypical population by Cytb: 0.11 and ATP: 0.13 distance. Therefore, they may be considered as independent species within the genus Phoxinus. We found the generic level genetic distance between Phoxinus and Rhynchocypris (Cytb: 0.24 and ATP: 0.68), which thus confirmed their independence. Genetic analyses revealed that one of the studied individuals of R. lagowskii shares the ATP haplotype with R. czekanowskii. The Cytb haplotype of this individual is also closest to that of R. czekanowskii, indicating an introgression between these forms and questioning their species status. The UPGMA and MP analysis of the selected osteological features confirmed the differentiation between Phoxinus and Rhynchocypris on the generic level. The results at lower taxonomic levels are not consistent with the identified genetic diversity, suggesting that osteological features may not be sufficient to distinguish forms at the intra-generic level.