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.
Highlights
Atlantic salmon (Salmo salar L.) aquaculture was initiated in the early 1970s and has grown into an internationally significant industry with a worldwide production exceeding 2.3 million tons in 2016 (FAO 2016)
The results of our simulations indicate that at domesticated salmon spawning intrusion levels of 5% and 10% (~1%–2% gene-flow per year), most of the phenotypic and demographic traits measured in the recipient wild population only displayed weak changes on a relatively short time scale (i.e., 50 years)
When the frequency of domesticated escapees on the spawning grounds was increased to 30% or 50% (~5%–9% gene-flow per year), were phenotypic and demographic changes clearly visible in the recipient wild population on this time scale
Summary
Atlantic salmon (Salmo salar L.) aquaculture was initiated in the early 1970s and has grown into an internationally significant industry with a worldwide production exceeding 2.3 million tons in 2016 (FAO 2016). Variations in these and other unidentified factors contribute to the observed interpopulation differences in introgression levels Another possibility is that, given that not all wild salmon home back to their native rivers (Stabell, 1984), strayers from relatively unaffected wild populations could buffer genetic changes in close-by populations that are subject to spawning intrusion of domesticated escapees. To gain a better understanding of the magnitude and timescale of changes in a range of phenotypic traits (survival and life-history traits such as size at age and age of maturity), underlying genotypes, and resultant demographic trajectories (i.e., numbers of fish) in wild salmon populations faced with different levels of spawning intrusion from domesticated escapees and continual natural selection. Scenario 1 2 3 4 5 6 7 8 straying among wild populations and the genetic admixture characteristics of strayers
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