Modelling the Consequences of Domestication-Introgression in Wild Populations Using Genetic Markers Under Varying Degrees of Selection.

Introgression of domesticated genomes influences the evolutionary trajectory of wild populations. Genetic markers are used to quantify admixture in wild populations subjected to introgression from non-native conspecifics. However, markers can be under direct and indirect selection which may influence admixture estimates and quantification of fitness consequences thereafter. We expanded the Atlantic salmon eco-genetic model IBSEM to compute individual fish phenotype and domestication admixture using markers under variable strengths of selection. Following 50 years of 5%-25% domesticated conspecifics on the spawning grounds, the recipient wild population showed an increase in adult size at age and a decline in adult abundance, both of which scaled with the degree of intrusion. In the following 50-year recovery period without further escapees, traits started to but did not completely revert to pre-impact levels. Neutral and weakly selected markers gave higher admixture estimates than markers under stronger degrees of selection. The disparity increased during the recovery period where neutral markers and their corresponding admixture estimates "lingered" in the wild population, whereas admixture based on markers under selection declined as the population recovered. During the recovery period, the strength in the relationship between individual fish admixture and size at age was also eroded when computed using neutral markers, but less so for the markers under selection. Collectively, these observations illustrate how markers under selection mirror the fitness and phenotypic changes in the population, while neutral markers reflect demographic history and can therefore not be uncritically used to infer fitness consequences. Our results also suggest that management guidelines used in Norway and some other countries, setting 10% domesticated escapees in a river and/or 10% domestication admixture in wild populations as the limit for a "large" impact, will provide a high level of protection for wild salmon populations.