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Farmed salmon escape and interbreed with wild Atlantic salmon on a large scale. We studied introgression of mitochondrial haplotypes from farmed Atlantic salmon originating from the Eastern Atlantic phylogenetic group to wild salmon of the Barents-White Sea (BWS) phylogenetic group. We find that farmed genetic introgression introduced novel, non-native haplotypes into the BWS phylogenetic group. The mitochondrial genome has important functional effects and is inherited as a haploid from the mother. Hence, the observed introgression across natural genetic barriers is expected to cause long- lasting functional maladaptation of the hybrids in the maternal line. As the use of farmed Atlantic salmon from non-native phylogenetic groups is widespread in aquaculture, the impact on wild Atlantic salmon may be more severe than previously recognized. Our results highlight the ecological risks of releasing non-native wild and domesticated animals. Key words: Atlantic salmon, aquaculture, genetic introgression, Salmo salar, phylogeny, haplotypes, Introduction Human-mediated gene flow is widespread and has detrimental effects on wild populations (Crispo et al. 2011; Ottenburghs 2021). Important and growing causes of human-mediated gene flow are escaped domesticated [...]

Evolution of iteroparity is shaped by the trade-off between current and future reproduction. We studied variation in iteroparity among 205 050 individual Atlantic salmon caught in 179 rivers spanning 14[degrees] of latitude. The proportion of repeat spawners (iteroparous individuals) averaged 3.8% and ranged from 0% to 26% across rivers. Females were more often repeat spawners than males and had lower cost of reproduction in terms of lost body mass between spawning events. Proportion of repeat spawners for a given sea age at maturity, and the ratio of alternate to consecutive repeat spawners, increased with increasing population mean sea age at maturity. By combining smolt age, sea age at maturity, and age at additional spawning events, we identified 141 unique life-history types, and repeat spawners contributed 75% of that variation. Our results show that repeat spawners are important for life-history variation and suggest that the association between mean sea age and the frequency of repeat spawning is adaptive rather than a pleiotropic side effect arising from selection on sea age. Key words: age at maturity, life-history evolution, local adaptation, repeat spawning, trade-off, Introduction Allocation of limited resources results in trade-offs shaping life-history evolution. One essential trade-off is the partition of energy between current and future reproduction (Stearns 1992). This trade-off plays out [...]

Thiamine deficiency is an ongoing issue across the Northern Hemisphere, causing reproductive failure in multiple salmonid populations. In the Baltic Sea, a large brackish water system in northern Europe, previous research has suggested that this deficiency is associated with lipid‐rich diets with a high proportion of docosahexaenoic acid (DHA, 22:6n‐3). The mechanism proposed is that a diet abundant in highly unsaturated fatty acids, such as DHA, depletes thiamine as an antioxidant defense in adult salmonids, rather than allocating thiamine to the offspring. In light of this existing hypothesis, we here explore the relationship between diet history and the related fatty acid (FA), profiles, and thiamine status of Atlantic salmon (Salmo salar L.) in three systems: the Baltic Sea, the North Atlantic Ocean, and Lake Vänern. Atlantic salmon inhabiting each system is known to have unique feeding histories and thiamine status. Our results showed that despite extensive sampling effort and distinct FA profiles, indicative of their diverse diets, there were no correlations between any FAs, including DHA, and the thiamine status of these populations. This finding does not support the above‐mentioned hypothesis that diets rich in easily oxidized FAs would lead to lower thiamine concentrations in salmon tissues. Additionally, we found that changes in the salmon FA profiles throughout their life cycle are consistent for both low‐thiamine populations from the Baltic Sea and medium‐thiamine populations from North Atlantic Ocean, suggesting that these changes might not be involved in thiamine deficiency development. [ABSTRACT FROM AUTHOR]

The ecological role of heritable phenotypic variation in free‐living populations remains largely unknown. Knowledge of the genetic basis of functional ecological processes can link genomic and phenotypic diversity, providing insight into polymorphism evolution and how populations respond to environmental changes. By quantifying the marine diet of Atlantic salmon, we assessed how foraging behaviour changes along the ontogeny, and in relation to genetic variation in two loci with major effects on age at maturity (six6 and vgll3). We used a two‐component, zero‐inflated negative binomial model to simultaneously quantify foraging frequency and foraging outcome, separately for fish and crustaceans diets. We found that older salmon forage for both prey types more actively (as evidenced by increased foraging frequency), but with a decreased efficiency (as evidenced by fewer prey in the diet), suggesting an age‐dependent shift in foraging dynamics. The vgll3 locus was linked to age‐dependent changes in foraging behaviour: Younger salmon with vgll3LL (the genotype associated with late maturation) tended to forage crustaceans more often than those with vgll3EE (the genotype associated with early maturation), whereas the pattern was reversed in older salmon. Vgll3LL genotype was also linked to a marginal increase in fish acquisition, especially in younger salmon, while six6 was not a factor explaining the diet variation. Our results suggest a functional role for marine feeding behaviour linking genomic diversity at vgll3 with age at maturity among salmon, with potential age‐dependent trade‐offs maintaining the genetic variation. A shared genetic basis between dietary ecology and age at maturity likely subjects Atlantic salmon populations to evolution induced by bottom‐up changes in marine productivity. [ABSTRACT FROM AUTHOR]

Males and females share many traits that have a common genetic basis; however, selection on these traits often differs between the sexes, leading to sexual conflict (1,2). Under such sexual antagonism, theory predicts the evolution of genetic architectures that resolve this sexual conflict (2-5). Yet, despite intense theoretical and empirical interest, the specific loci underlying sexually antagonistic phenotypes have rarely been identified, limiting our understanding of how sexual conflict impacts genome evolution (3,6) and the maintenance of genetic diversity (6,7). Here we identify a large effect locus controlling age at maturity in Atlantic salmon (Salmo salar), an important fitness trait in which selection favours earlier maturation in males than females (8), and show it is a clear example of sex-dependent dominance that reduces intralocus sexual conflict and maintains adaptive variation in wild populations. Using high-density single nucleotide polymorphism data across 57 wild populations and whole genome re-sequencing, we find that the vestigial-like family member 3 gene (VGLL3) exhibits sex-dependent dominance in salmon, promoting earlier and later maturation in males and females, respectively. VGLL3, an adiposity regulator associated with size and age at maturity in humans, explained 39% of phenotypic variation, an unexpectedly large proportion for what is usually considered a highly polygenic trait. Such large effects are predicted under balancing selection from either sexually antagonistic or spatially varying selection (9,10). Our results provide the first empirical example of dominance reversal allowing greater optimization of phenotypes within each sex, contributing to the resolution of sexual conflict in a major and widespread evolutionary trade-off between age and size at maturity. They also provide key empirical evidence for how variation in reproductive strategies can be maintained over large geographical scales. We anticipate these findings will have a substantial impact on population management in a range of harvested species where trends towards earlier maturation have been observed., The importance of balancing selection in maintaining variation in fitness-related traits, which are expected to be under strong selection, is a long-standing question in evolutionary biology (7,11,12), with recent models [...]

138 Atlantic salmon (Salmo salar) captured in the Advent Fjord off Svalbard were genetically assigned to two main clusters of European salmon. Two-thirds were assigned to salmon rivers in Finnmark (the northernmost county in Norway) and the rest to salmon rivers further south in Norway. The genetic assignment was based on genetic profiles from 60 Norwegian rivers. The two clusters correspond to two larger genetic groupings: the Barents-White seas and Atlantic groupings. Thus, we cannot rule out other populations from these groupings as sources of Atlantic salmon at Svalbard. Svalbard salmon assigned to the two genetic groupings differed in ecological and phenological traits, with highest smolt age and lowest postsmolt growth in the Finnmark salmon cluster. High smolt ages in both groups, however, suggest a northern origin of most individuals in the sample. Although Atlantic salmon have sporadically been observed in the Arctic Ocean at earlier times, the high abundance outlined here seems to be a recent phenomenon, suggesting a northward penetration caused by climate change. Cent-trente-huit saumons atlantiques (Salmo salar) captures dans le fiord de l'Avent au large de Svalbard ont ete affectes genetiquement a deux grands groupes de saumons europeens. Deux tiers d'entre eux ont ete affectes a des rivieres a saumons du Finnmark (le comte le plus nordique de la Norvege) et les autres, a des rivieres a saumons norvegiennes situees plus au sud. Cette affectation genetique repose sur les profils genetiques de 60 rivieres norvegiennes. Ces deux groupes correspondent a deux regroupements genetiques plus larges, celui des mers de Barents-Blanche et celui de l'Atlantique. La possibilite que des saumons atlantiques de Svalbard proviennent d'autres populations de ces regroupements ne peut donc etre exclue. Les saumons de Svalbard affectes aux deux regroupements genetiques presentent des caracteres ecologiques et phenologiques distincts, le groupe de Finnmark presentant les ages de saumoneaux les plus grands et la croissance post-saumoneau la plus faible. Les ages de saumoneaux eleves des deux groupes suggerent toutefois une origine nordique pour la plupart des individus de l'echantillon. Bien que des saumons atlantiques aient sporadiquement ete observes dans l'ocean Arctique par le passe, leur forte abondance relevee dans la presente etude semble constituer un phenomene recent qui indiquerait une penetration vers le nord causee par les changements climatiques. [Traduit par la Redaction], Introduction Historically, the Arctic Ocean off Svalbard (Spitsbergen) was expected to be north of the oceanic distribution of Atlantic salmon (Salmo salar) (MacCrimmon and Gots 1979). New surveys have, however, [...]