Biogeographic insights from a genomic survey of Salmo trouts from the Aralo-Caspian regions

The eastern-most members of the Salmo trutta species complex in the Aralo-Caspian Sea region were studied to infer their population genetic structure and biogeographic origin. A total of 68 individuals collected from Iranian endorheic inland basins (Namak and Urmia lakes), tributaries of the Caspian (Haraz, Kura, Samur, Volga, and Ural river drainages) and Aral (Amu River) seas, and the Baltic Sea basin were genotyped using 26,202 SNPs via Genotyping-by-Sequencing. The data were analyzed using admixture, discriminant analysis of principal components (DAPC), analysis of molecular variance (AMOVA), species tree, genetic differentiation ( F ST ), allele frequency difference (AFD), and neighbor network approaches. Trout in the southern Caspian Sea basin differ from those of the western and northern Caspian Sea. Based on our results, the Lake Namak trout is divergent from the southern and western Caspian trout populations. Aral Sea and Lake Namak trouts likely originated from the northern and southern Caspian Sea populations, respectively. Although only few populations were considered in this study, six conservation/management units of trouts are proposed.