Ancestral sockeye salmon started in rivers and then invaded lakes

Sockeye salmon are found in many lakes and rivers in the northern Pacific Ocean, and have radiated outwards into regions formerly under glaciers during the most recent ice age. There are three main ecotypes: river-spawners (that migrate directly from the ocean to spawn in rivers); beach-spawners (that spawn on beaches in lakes) and tributary-spawners (that spawn in river tributaries that feed into lakes). Now, a new genetic study examines sockeye salmon from these 3 ecotypes that come from 32 separate populations in 7 major river systems. For each fish, key regions of the DNA were genotyped (reading the DNA letters) that are not subject to selective pressure, that are likely involved in adaptive divergence among populations from a single drainage (“genomic islands”), and that are important for the immune system. There was strong evidence of selection, but this did not vary systematically by ecotype. The resulting data show links between distant populations of river-spawning sockeye salmon, which provides evidence that river-spawners are the ancestral form of sockeye salmon, and that other ecotypes arose from adaptive radiation into areas that came available as glaciers receded. The work was led by current and former SAFS students and postdocs Wes Larson, Tyler Dann, and Garrett McKinney, and SAFS professors James Seeb and Lisa Seeb, and appears in the journal Molecular Ecology.

Locations of the sampled sockeye salmon used in the study.
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