A new super narrow-ranged endemic Phoxinus minnow (Leuciscidae) from the Caucasus

Abstract

A new species, Phoxinus ayukensis sp. nov., from the Kuban basin (Northwestern Caucasus) is described. This species has an extremely narrow range of approximately 5-7 km in a seasonally almost drying stream within the karstic region. The new species has a moderate genetic distance in cytochrome b mtDNA (p-distance = 0.026 ± 0.005) from geographically and genetically close species in the Kuban basin-P. adagumicus-and differs from all known Phoxinus species by a highly increased number of scales in the lateral series: 87-105 (mean 97.7), differs from other species from Eastern Europe and the Caucasus (P. adagumicus, P. chrysoprasius, P. colchicus, and P. isetensis) by an increased frequency of occurrence of seven rays in the pelvic fin (ca. 35%) and an increased number of scales between bases of dorsal and anal fins (32-41, mean 36.7). Morphologically, the new species is the most different from the other Caucasian species, but it is closer to the Northern minnow P. isetensis; that might be explained by phenotypic convergence caused by adaptation to cold waters. The range of the new species is limited by waterfalls in the upper reach of the Ayuk Stream, where subterranean water outlets probably contributed to its survival. The role of Pleistocene glaciations in shaping the modern distribution and environmental differences in evolutionary divergence of Caucasian Phoxinus is highlighted. Low genetic diversity coupled with extremely limited range within the seasonally half-drying stream suggests a high rank of protection for new species.