Cryptic species of Ponto-Caspian bighead goby of the genus Ponticola (Gobiidae)

Abstract

Based on karyological data, the validity of the species Ponticola iljini is re-established; its distribution is limited to the coast of the Mangyshlak Peninsula. The morphological characteristics and the basic color pattern of P. iljini are very similar to P. kessleri from the Black Sea basin and P. gorlap which inhabits the northern, western, and southern Caspian Sea. These three allopatric species have ctenoid scales to varying degrees on the crown and nape (100% presence in P. kessleri and complete absence in P. iljini), and there are small differences in the shape of the head, the thickness of the caudal peduncle, and in the form of otoliths; at the same time, they are clearly differentiated by the number of chromosomes and the presence of marker submetacentric chromosomes in P. iljini. In the phylogenetic tree based on the variation of the mitochondrial cytochrome b gene in the main species of Ponto-Caspian gobies, P. iljini, P. gorlap, and P. kessleri form independent phyletic lineages within a clade of the genus Ponticola. Redescription of the species P. iljini is provided; the possible causes of the identified intraspecific variation in the shape of the otoliths and temporal bounderies of the beginning of divergence of the considered three cryptic species, as well as isolating barriers that led to allopatric speciation, are discussed.