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      Modeling fitness changes in wild Atlantic salmon populations faced by spawning intrusion of domesticated escapees

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          Abstract

          Genetic interaction between domesticated escapees and wild conspecifics represents a persistent challenge to an environmentally sustainable Atlantic salmon aquaculture industry. We used a recently developed eco‐genetic model (IBSEM) to investigate potential changes in a wild salmon population subject to spawning intrusion from domesticated escapees. At low intrusion levels (5%–10% escapees), phenotypic and demographic characteristics of the recipient wild population only displayed weak changes over 50 years and only at high intrusion levels (30%–50% escapees) were clear changes visible in this period. Our modeling also revealed that genetic changes in phenotypic and demographic characteristics were greater in situations where strayers originating from a neighboring wild population were domestication‐admixed and changed in parallel with the focal wild population, as opposed to nonadmixed. While recovery in the phenotypic and demographic characteristics was observed in many instances after domesticated salmon intrusion was halted, in the most extreme intrusion scenario, the population went extinct. Based upon results from these simulations, together with existing knowledge, we suggest that a combination of reduced spawning success of domesticated escapees, natural selection purging maladapted phenotypes/genotypes from the wild population, and phenotypic plasticity, buffer the rate and magnitude of change in phenotypic and demographic characteristics of wild populations subject to spawning intrusion of domesticated escapees. The results of our simulations also suggest that under specific conditions, natural straying among wild populations may buffer genetic changes in phenotypic and demographic characteristics resulting from introgression of domesticated escapees and that variation in straying in time and space may contribute to observed differences in domestication‐driven introgression among native populations.

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          Most cited references57

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          A review of local adaptation in Salmonidac, with particular reference to Pacific and Atlantic salmon

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            A critical review of adaptive genetic variation in Atlantic salmon: implications for conservation.

            Here we critically review the scale and extent of adaptive genetic variation in Atlantic salmon (Salmo salar L.), an important model system in evolutionary and conservation biology that provides fundamental insights into population persistence, adaptive response and the effects of anthropogenic change. We consider the process of adaptation as the end product of natural selection, one that can best be viewed as the degree of matching between phenotype and environment. We recognise three potential sources of adaptive variation: heritable variation in phenotypic traits related to fitness, variation at the molecular level in genes influenced by selection, and variation in the way genes interact with the environment to produce phenotypes of varying plasticity. Of all phenotypic traits examined, variation in body size (or in correlated characters such as growth rates, age of seaward migration or age at sexual maturity) generally shows the highest heritability, as well as a strong effect on fitness. Thus, body size in Atlantic salmon tends to be positively correlated with freshwater and marine survival, as well as with fecundity, egg size, reproductive success, and offspring survival. By contrast, the fitness implications of variation in behavioural traits such as aggression, sheltering behaviour, or timing of migration are largely unknown. The adaptive significance of molecular variation in salmonids is also scant and largely circumstantial, despite extensive molecular screening on these species. Adaptive variation can result in local adaptations (LA) when, among other necessary conditions, populations live in patchy environments, exchange few or no migrants, and are subjected to differential selective pressures. Evidence for LA in Atlantic salmon is indirect and comes mostly from ecological correlates in fitness-related traits, the failure of many translocations, the poor performance of domesticated stocks, results of a few common-garden experiments (where different populations were raised in a common environment in an attempt to dissociate heritable from environmentally induced phenotypic variation), and the pattern of inherited resistance to some parasites and diseases. Genotype x environment interactions occurr for many fitness traits, suggesting that LA might be important. However, the scale and extent of adaptive variation remains poorly understood and probably varies, depending on habitat heterogeneity, environmental stability and the relative roles of selection and drift. As maladaptation often results from phenotype-environment mismatch, we argue that acting as if populations are not locally adapted carries a much greater risk of mismanagement than acting under the assumption for local adaptations when there are none. As such, an evolutionary approach to salmon conservation is required, aimed at maintaining the conditions necessary for natural selection to operate most efficiently and unhindered. This may require minimising alterations to native genotypes and habitats to which populations have likely become adapted, but also allowing for population size to reach or extend beyond carrying capacity to encourage competition and other sources of natural mortality.
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              Risk assessment of the environmental impact of Norwegian Atlantic salmon farming

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                Author and article information

                Contributors
                kevin.glover@hi.no
                Journal
                Evol Appl
                Evol Appl
                10.1111/(ISSN)1752-4571
                EVA
                Evolutionary Applications
                John Wiley and Sons Inc. (Hoboken )
                1752-4571
                23 March 2018
                July 2018
                : 11
                : 6 ( doiID: 10.1111/eva.2018.11.issue-6 )
                : 1010-1025
                Affiliations
                [ 1 ] Department of Engineering University of Birmingham Birmingham UK
                [ 2 ] Department of Biological Sciences University of Bergen Bergen Norway
                [ 3 ] Institute of Marine Research Bergen Norway
                [ 4 ] International Institute for Applied Systems Analysis (IIASA) Laxenburg Austria
                [ 5 ] Freshwater Fisheries Laboratory Marine Scotland Pitlochry UK
                [ 6 ] Research Faculty of Agriculture Hokkaido University Sapporo Japan
                Author notes
                [*] [* ] Correspondence

                Kevin A. Glover, Institute of Marine Research, Bergen, Norway.

                Email: kevin.glover@ 123456hi.no

                Author information
                http://orcid.org/0000-0003-2928-3940
                http://orcid.org/0000-0002-8608-5652
                http://orcid.org/0000-0002-7541-1299
                Article
                EVA12615
                10.1111/eva.12615
                5999203
                29928306
                f112a3ee-eea7-44b8-ab06-6874d68ca5ca
                © 2018 The Authors. Evolutionary Applications published by John Wiley & Sons Ltd

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 29 October 2017
                : 11 February 2018
                Page count
                Figures: 6, Tables: 1, Pages: 16, Words: 10441
                Funding
                Funded by: Norges Forskningsråd (INTERACT)
                Award ID: 200510
                Categories
                Original Article
                Original Articles
                Custom metadata
                2.0
                eva12615
                July 2018
                Converter:WILEY_ML3GV2_TO_NLMPMC version:version=5.4.1.1 mode:remove_FC converted:13.06.2018

                Evolutionary Biology
                admixture,aquaculture,farmed escapees,gene‐flow,genetic interactions
                Evolutionary Biology
                admixture, aquaculture, farmed escapees, gene‐flow, genetic interactions

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