Patterns of Phenetic Diversity and Taxonomy of the Ide Leuciscus idus (Cypriniformes, Cyprinidae) from Water Bodies of Russia and Adjacent Countries

Using the methods of population morphology, we have studied the structure of phenetic diversity of the ide Leuciscus idus (L.) from the water bodies of the Russian Federation and some neighboring countries. We analyzed our own collection and literature data on the meristic characters of external morphology and the axial skeleton, as well as the pharyngeal teeth formula. The main features contributing to population differentiation are the number of lateral line scales, total vertebrae count, and caudal and precaudal vertebrae ratio. It is shown that the strong positive relationships of the first two features with the geographical latitude of fish habitats is associated, first and foremost, not with the direct influence of physical factors functionally dependent on latitude, but with particular (sub)speciation processes in river basins and the dispersal of evolutionarily derived forms to the north. The results are discussed in terms of evolutionary trends in the Leuciscinae subfamily and call for a taxonomic revision of the L. idus species in its current volume with the elevation of the former subspecies L. idus oxianus to the species rank.