The Problems of DNA-Barcoding the Shads of genus Alosa (Alosidae) of the Ponto-Caspian Basin

Numerous studies show that species identification of representatives of the genus Alosa using various genetic markers is often difficult and the search for more specific biomarkers is required. For the first time we analyzed polymorphism of COI gene fragment of mitochondrial DNA of two representatives of this genus (A. tanaica and A. kessleri), supplemented with new data on A. immaculata, from the waters of the Ponto-Caspian basin in comparative aspect with other representatives of the herring (Clupeoidea) genera Alosa, Clupea, Clupeonella, Sprattus, and Sardinops. The main result was the conclusion that within the genus Alosa, it is not possible to identify species using the marker used. On the one hand, specimens collected from morphologically distinct individuals and identified as different species have the same haplotypes. On the other hand, samples belonging to different species differ from each other by an insignificant number of nucleotide substitutions and do not form independent clades on the phylogram and haplotype network. This indicates the absence of genetic differentiation between the studied samples of herrings of genus Alosa into separate species and species groups when using DNA barcoding based on the COI gene. The reasons for such a phenomenon may be the following: 1) incorrect identification of species in catches, since shads (Alosidae) have high morphological flexibility and in many species, the main external morphological characters often overlap; 2) recent time of speciation by the standards of biological evolution for shads of genus Alosa; 3) difference in proportion of interspecific hybrids, which can vary significantly between populations of the same species.