Scientists from the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences (IEE RAS) and the I.D. Papanin Institute of Inland Water Biology of the Russian Academy of Sciences (IBW RAS) have described a new species of minnow — Phoxinus ayukensis — with an extremely narrow range. It lives only in the upper reaches of the Ayuk Creek, which is part of the Psekups River system, a tributary of the Kuban, in a 5-7 km long section of the riverbed, limited by waterfalls and fed by karst springs with cold water. The Ayuk Creek, where the new species was discovered, originates near the Bolshaya Phanagoria Cave. The population attracted attention back in the 1930s, when researchers noticed its geographical isolation, but only modern comprehensive analysis has revealed its uniqueness.
The Ayuk minnow differs from other known minnows by a significantly increased number of scales in the lateral line and a high proportion of individuals with a reduced number of rays in the ventral fins. At the same time, it is characterized by a moderate genetic distance in the mtDNA cytochrome b gene from a geographically and genetically close species, also inhabiting the Kuban Basin - the Adagum minnow P. adagumicus.
“The stable temperature of underground karst waters could have helped the species survive climate collisions, especially during glacial-interglacial periods, and its very low values (about 8 degrees) could have contributed to an increase in the number of scales. Isolation and small population size are possibly associated with the founder effect and the population passing through a “bottleneck,” which led to a decrease in genetic diversity and accelerated gene drift. This could have contributed to the rapid consolidation of mutations and the emergence of pronounced morphological differences,” said Boris Levin, PhD in Biology, leading researcher at the IEE RAS.
The stream where the new minnow species lives dries up in the summer, turning into a chain of puddles. The population is vulnerable: it has low genetic diversity, and a decrease in water availability due to drought could put the species at risk of extinction. This discovery, along with the example of the Kildin cod, shows how the isolation of small populations in special environmental conditions leads to the formation of new forms and species, and emphasizes the importance of preserving the fragile ecosystems of the Caucasus, where groundwater outlets play a key role in the formation and maintenance of aquatic biodiversity.
The article is published in the open access journal Zoosystematics and Evolution: A new super narrow-ranged endemic Phoxinus minnow (Leuciscidae) from the Caucasus Oleg N. Artaev, Ilya S. Turbanov, Aleksey A. Bolotovskiy, Alexander A. Gandlin, Boris A. Levin, 10.3897/zse.101.153548 , Zoosystematics and Evolution 101(3): 1137-1154.
The work was supported by the Russian Science Foundation grant No. 23-14-00128.
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