Selection against individuals from genetic introgression of escaped farmed salmon in a natural population of Atlantic salmon.

Sten Karlsson,Tonje Aronsen,Ola H Diserud,Kjetil Hindar,Tor F Næsje,Ola Ugedal,Sebastian Wacker,Eva M Ulvan

doi:10.1111/eva.13213

Sten Karlsson, Tonje Aronsen + Show 6 more

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https://doi.org/10.1111/eva.13213

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Abstract

The viability of wild Atlantic salmon populations is threatened by genetic introgression from escaped farmed salmon. Farmed Atlantic salmon are genetically improved for important commercial traits and a life in captivity but are poorly adapted to the natural environment. The rate of gene flow from escaped farmed to wild salmon depends on their spawning success and on offspring survival at various life stages. We here investigate relative survival of introgressed juvenile Atlantic salmon (parr) in a river in northern Norway. The studied population has experienced genetic introgression from farmed salmon for about four generations (20 years). We followed two cohorts of parr from the year of hatching (0+) to the age of 2 years (2+). Farmed genetic introgression was quantified at the individual level and on a continuous scale using diagnostic SNPs. Population‐level genetic introgression decreased from 0+ to 2+ by 64% (2011 cohort) and 37% (2013 cohort). This change was driven by a 70% (2011 cohort) and 49% (2013 cohort) lower survival from age 0+ to 2+ in introgressed parr compared to parr of wild origin. Our observations show that there is natural selection against genetic introgression with a potential cost of lower productivity.

Highlights

Domesticated animals that escape from captivity or are released intentionally may hybridize with wild conspecifics, leading to unidirectional gene flow into wild populations
The results show that introgressed parr had a lower survival than wild parr in River Alta
In line with our results, introgressed parr had a lower survival than wild parr in Canada (Sylvester et al, 2019; Wringe et al, 2018)

Summary

Introduction

Domesticated animals that escape from captivity or are released intentionally may hybridize with wild conspecifics, leading to unidirectional gene flow into wild populations. Examples of genetic introgression from domesticated animals into wild populations include mammals (Anderson et al, 2019; Kidd et al, 2009), birds (Brisbin & Peterson, 2007; Wu et al, 2020), fish (Letourneau et al, 2018) and insects (Seabra et al, 2019). Genetic introgression from domesticated animals alters the gene pool of wild populations and may constrain their viability and evolutionary potential (Glover et al, 2017; Naylor et al, 2005). Domesticated animals may originate from a limited set of founder populations and from a geographical range that does not reflect the genetic diversity of the species (Hindar et al, 1991). Reduced genetic diversity and non- native origin are commonly found in captive-bred animals that

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