Comparative Analysis of Morphological Diversification in Large African Barbs of the Genus Barbus (Labeobarbus auctorum, Cyprinidae) and Altai Osmans of the Genus Oreoleuciscus (Leuciscidae)

The study of diversity in characters of the skull in generalized and specialized morphotypes of the large African barbs Barbus (Labeobarbus auctorum) in Ethiopia is carried out using the multivariate analysis methods. It has been proven that in Lake Tana exhibiting great diversity in morphotypes, the eigenvector loadings on the first principal component of characters of bones, which form the jaws, compose a distinct self-standing cluster in specimens of a generalized form reaching over 15 cm in length. In barbs inhabiting other lakes, where only a generalized form is found, the lack of such cluster is observed, while the eigenvector loadings on the second principal component generate a cluster similar in composition. The same pattern is discovered in the Altai osmans (genus Oreoleuciscus) in Lake Orog within the Central Asian Closed Basin (Mongolia). In this case, however, the specimens of the generalized form tend to exhibit the characters of a bigmouth form after transition to feeding on fish whereas the progeny of bigmouth barbs in Lake Tana exhibit the parental characters even in the aquarium-based experiments. It is assumed that in the Altai osmans from Lake Orog we observe an early stage of morpho-ecological divergence between forms, when it is still reversible, while the divergence at a later stage, when it is irreversible, is detected in the barbs from Lake Tana, which may be regarded as an example of genetic assimilation.