Pathways of invasion of the threespine stickleback (Gasterosteus aculeatus) into the basins of the Black and Caspian seas

Studying the routes of invasion of the threespine stickleback is important both because it serves as a model species in evolutionary research and because it may play a substantial role in ecosystems. The goal of this study was to determine the recent pathways of threespine stickleback invasion into the Black and Caspian Sea basins. The partial COI and cyt b mitochondrial gene sequences and the mtDNA region between them (a total of 9926 bp) have been analyzed in a priori separate phylogenetic lineages, Black Sea and American ones. The results indicate that similar sequences of the COI gene may result from parallel evolution in different lineages. The basins of the Volga and Dnieper, the largest rivers of the Ponto-Caspian basin, are currently inhabited only by carriers of the European lineage haplotypes; this agrees with the data on the disappearance of aboriginal stickleback populations from these river basins in the first half of the twentieth century. Only Black Sea lineage haplotypes have been found in stickleback from the recently formed populations of the Caspian Sea coast. The results show that alien conspecifics may substantially affect the genetic structure of threespine stickleback populations in the native species range.