Spatial and temporal genetic structure of a river‐resident Atlantic salmon ( Salmo salar) after millennia of isolation

• Published in: Ecology and Evolution
• Main Authors: Sandlund, Odd Terje, Karlsson, Sten, Thorstad, Eva B., Berg, Ole Kristian, Kent, Matthew P., Norum, Ine C. J., Hindar, Kjetil
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: Almo; Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1002/ece3.1040; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fece3.1040; https://onlinelibrary.wiley.com/doi/pdf/10.1002/ece3.1040; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ece3.1040

Abstract The river‐resident S almo salar (“småblank”) has been isolated from other A tlantic salmon populations for 9,500 years in upper R iver N amsen, N orway. This is the only E uropean A tlantic salmon population accomplishing its entire life cycle in a river. Hydropower development during the last six decades has introduced movement barriers and changed more than 50% of the river habitat to lentic conditions. Based on microsatellites and SNP s, genetic variation within småblank was only about 50% of that in the anadromous A tlantic salmon within the same river. The genetic differentiation ( F ST ) between småblank and the anadromous population was 0.24. This is similar to the differentiation between anadromous A tlantic salmon in E urope and N orth A merica. Microsatellite analyses identified three genetic subpopulations within småblank, each with an effective population size N e of a few hundred individuals. There was no evidence of reduced heterozygosity and allelic richness in contemporary samples (2005–2008) compared with historical samples (1955–56 and 1978–79). However, there was a reduction in genetic differentiation between sampling localities over time. SNP data supported the differentiation of småblank into subpopulations and revealed downstream asymmetric gene flow between subpopulations. In spite of this, genetic variation was not higher in the lower than in the upper areas. The meta‐population structure of småblank probably maintains genetic variation better than one panmictic population would do, as long as gene flow among subpopulations is maintained. Småblank is a unique endemic island population of Atlantic salmon. It is in a precarious situation due to a variety of anthropogenic impacts on its restricted habitat area. Thus, maintaining population size and avoiding further habitat fragmentation are important.