ИСТИНА

Earlier, karyological studies proved Ponto-Caspian Bighead goby to be represented by two independent species very similar in their morphology and colour pattern: Ponticola kessleri in the Black Sea basin and Ponticola gorlap in the Caspian Sea. Populations from the Mangyshlak Peninsula (Eastern Caspian), morphologically identified as P. gorlap, were subjected to karyological study and phylogenetic analysis (based on PCR of a 1098 bp fragment of mtDNA cytochrome b gene) to define their taxonomic status. Seven karyological morphs with 2n varied from 38 to 44 and stable number of chromosome arms NF=46 were revealed among specimens from the inshore Eastern Caspian Sea regions and the Karakol Lake. They noticeably differ from P. gorlap distributed in the western, southern and northern Caspian, as well as from P. kessleri from the Black Sea basin, in the number of chromosomes and by the presence of one pare of marker submetacentrics. Phylogenetic relationships constructed by using the neighbour joining algorithm and methods of maximum parsimony and maximum likelihood demonstrate P. kessleri, P. gorlap, and eastern Caspian gobies as three separate phylogenetic lineages within the clade of the genus Ponticola. These data confirm the validity of the species P. iljini previously described on the type specimens from the Caspian Sea off the Mangyshlak Peninsula. P. iljini, P. gorlap, and P. kessleri form a group of allopatric cryptic species with low morphological divergence observed in the development of ctenoid scales on the head and the shape of head and body. Independent evolution of the most closely related P. iljini and P. gorlap should be considered in relation to their isolation by high salinity barriers formed by the Mërtvyj Kultuk and Kajdak bays to the north of Mangyshlak and the Kara-Bogaz-Gol Bay to the south. This could happen not earlier than 2 MYA.