Counter-Spread Invasion of Nine-Spined Stickleback (Pungitius pungitius) and Southern Nine-Spined Stickleback (Pungitius platygaster) (Gasterosteidae) in the Water Bodies of the Ponto-Caspian Basin

Using the analysis of the diversity of the mitochondrial gene COI, it was revealed that the nine-spined stickleback invaded the Dnieper basin from the Baltic Sea basin and invaded the Volga basin from the same basin (the Baltic Sea) or, less likely, from the White Sea basin. Apparently, these migrations occurred recently via canals built in the late 18th–early 19th centuries. Analysis of the literature confirms that both the nine-spined stickleback and the closely related species, the southern nine-spined stickleback, which has spread from the south, are now widespread in the Volga and Dnieper basins. In both basins, the ranges of these two fish species now overlap and hybrid zones are likely to emerge in those areas.