Linking Ancient Refugia to Modern Diversity: Evidence of Multi-origin Postglacial Expansion of Sockeye Salmon on the Asian Range
Sockeye salmon (Oncorhynchus nerka) is a traditional object of fishery in the northern Pacific, but its island populations now face emerging threats from territories development and escalating risks of unregulated fishing. The present study aims to assess the current status of Kuril island populations associated with the biogeographical processes in the past. We analyzed diversity distribution of the D-loop sequence and three mtSNPs localized in the Cytb and COI genes in sockeye salmon populations across the North Pacific. mtDNA variants were grouped into two distinct lineages: haplogroups 10T and 13T. Their distribution suggests an Asian origin for the 10T lineage and a North American origin for the 13T haplogroup. Testing the biogeographical scenarios support recurrent postglacial expansions of North American strains into the southernmost territories of the Asian range during the last two glacial cycles. Concurrently, during the Holocene transgression, there were two centers of sockeye salmon radiation in Asia associated with the refugium in the Kamchatka River basin and a minor cryptic refugium in the Hokkaido region. We also propose an island bridge hypothesis to explain dispersal of 10T-lineage from the Kamchatka River basin into Cook Inlet and Alaska Peninsula watersheds via the Aleutian Islands.