Biology subjects

Primmer, C. R.

Publications and source records attributed to Primmer, C. R..

At least 19 recordsLinked to original sources

bioRxiv2026

The influence of parental and genotype effects on early survival and development in Atlantic salmon

Parental qualities can influence the development and fitness of their offspring via genetic and non-genetic effects. Although these effects are often linked to parental phenotypes, the effect of parental genetic variation linked with relevant phenotypes is less well understood. We performed full factorial crosses based on parental genotypes for an age-at-maturity-related gene, vgll3, to investigate how the parental genotypes influence Atlantic salmon (Salmo salar) offspring survival, growth, and development in their early life. Beyond the connection with age at maturity, the additional association between vgll3 and body condition in Atlantic salmon offers a potential pathway by which the maternal vgll3 genotype could influence offspring early life fitness. Combined with measurements of maternal phenotype and egg characteristics, the crossing design therefore allowed us to disentangle the maternal and paternal genetic and non-genetic contributions to variation in offspring survival and phenotypic traits. The phenotypic traits measured were hatching length and yolk sac area, growth, and yolk sac consumption and conversion efficiency. Parental vgll3 genotype did not influence the majority of our measured egg traits or alevin traits except for a genetic effect of paternal vgll3 genotype on offspring survival, whereby the paternal late maturation allele was associated with higher survival. Maternal effects were strongest for survival and for traits associated with hatching and weaker for alevin growth and yolk sac usage. Paternal effects on the measured alevin traits were negligible. The results from our study demonstrate that both maternal and paternal effects have the potential to influence offspring early life fitness traits.

evolutionary biology↗

bioRxiv2026

Extremely low effective population size in a captive-bred population: partial mitigation through management practices

1Effective population size (Ne) is a critical parameter for evaluating the evolutionary and persistence potential of endangered populations and for designing sustainable conservation strategies. Captive breeding and release programs are widely used across taxa to reduce risk of extinction when natural reproduction is insufficient or no longer possible, making it essential to assess their consequences. We used the case study of the landlocked Saimaa salmon (Salmo salar), one of the most critically en-dangered salmonid populations in Europe, with unique evolutionary significance due to its isolation from other populations since the last glaciation. Using long-term demographic data (1969-2024) from wild-caught founders of a captive breeding and release program, we estimated the effective population size under multiple scenarios of variance in reproductive success. Across scenarios, Ne ranged from 33 to 81 individuals, representing 32%-75% of the census size. Captive breeding practices aimed at equalizing parental contributions during fertilization and early life stages increased Ne by 12% compared to natural reproductive conditions. However, variation in survival after early developmental stages, typically beyond direct management control, remained a key determinant of Ne. Despite recent increases in the number of founders, the population remains genetically vulnerable due to historical bottlenecks. These results highlight that while captive breeding programs can partially mitigate genetic risks, their effectiveness depends critically on both controlled and uncontrolled sources of variance in reproductive success. Strengthening such programs may require combining breeding management with habitat restoration and, where appropriate, genetic rescue to ensure the long-term evolutionary potential of such unique and endangered populations.

evolutionary biology↗

bioRxiv2026

A major life-history locus underlies genotype-by-environment variation in growth across water temperatures

Rapid environmental change is exposing organisms to conditions that do not match those under which they evolved, making it increasingly important to understand how genetic variation shapes phenotypic responses to environmental stress. Since most phenotypic traits arise from interactions between genetic variation and the environments experienced throughout an organisms lifetime, understanding the genetic architecture of these interactions is central to predicting how populations will respond to novel environments. While genotype-by-environment interactions (GxE) are well studied in quantitative genetics, identifying specific loci that contribute to environmentally dependent trait expression remains rare. Salmonids already exhibit a wide portfolio of plastic life-history strategies, reflecting adaptation to highly heterogeneous environments, yet it remains unclear whether known major-effect loci involved in life-history regulation also contribute to variation in plastic responses to environmental change. One such major-effect locus is the transcription factor six6, which has been repeatedly associated with variation in age at maturity across multiple populations of rainbow trout (Oncorhynchus mykiss). Since maturation timing is closely linked to growth trajectories and patterns of energetic allocation during early development, allelic variation at this locus may also influence growth responses to warming conditions. Here, we test this hypothesis using a common-garden experiment in which 6 months old juvenile rainbow trout were reared under current and warming (+2{degrees}C) temperature regimes. By quantifying genotype-specific reaction norms across environments, we show that six6 genotype contributes to environmentally dependent variation in growth and body composition, with individuals heterozygous for the six6 locus showing a distinct and steeper response to warming relative to homozygotes. These findings provide evidence that a major life-history gene shapes plastic responses to thermal stress in juvenile rainbow trout, with novel implications for how standing genetic variation at in large-effect loci may influence population-level responses to climate warming.

evolutionary biology↗

bioRxiv2025

Selection against dispersers: Sex, age and origin-dependent fitness differences in wild Atlantic salmon

Local adaptation is often portrayed as uniform fitness disadvantages of immigrants relative to residents. Yet dispersal costs vary with origin, sex, and life-history traits, shaping the balance between gene flow and adaptation. We quantified these heterogeneous costs by comparing the reproductive success of local and immigrant individuals using a 15-year genetic pedigree of Atlantic salmon (Salmo salar), including over 1,100 adults and 3,400 juveniles. Immigrants represented 19.5% of adults, showed male-biased dispersal, and averaged 15% lower reproductive success than locals. However, outcomes were strongly origin-dependent: immigrants from some populations suffered severe fitness costs while others matched or exceeded locals. Sex and life-history further modulated reproductive success: male immigrants underperformed local males, whereas multi-sea-winter females often equaled or outperformed female residents. Immigrant males partially compensated their fitness offset by acquiring more mates. These findings highlight that, while local adaptation promotes philopatry, immigrants origin effects should be considered in gene-flow adaptation dynamics.

evolutionary biology↗

bioRxiv2025

A Comprehensive Analysis of Atlantic Salmon Gonad and Pituitary Transcriptomes Identifies Novel Players in Sexual Maturation

BackgroundSexual maturation is a key developmental process important for reproductive success. Understanding the molecular mechanisms behind variation in sexual maturation can provide insights into reproductive biology and how life history variation is encoded in the genome. Atlantic salmon (Salmo salar) has become an excellent sexual maturation research model due to its diversity of life history strategies and its ecological and economic importance. A major challenge has been the lack of a comprehensive transcriptional investigation of reproductive tissues that captures the dynamic transcriptional changes across individuals, tissues, and developmental stages. Long non-coding RNAs (lncRNAs) also play crucial roles in maturation, yet their functions in salmon maturation remain underexplored. ResultsIn this study, we sequenced 98 transcriptomes and found substantial transcriptomic complexity in the gonad and pituitary tissues of Atlantic salmon. We identified transcripts corresponding to 2,364 putative newly characterized protein-coding genes and 4,421 putative long intergenic non-coding RNAs (lincRNAs), many with tissue-specific expression. Gene co-expression network analysis (WGCNA) revealed tissue-specific gene network modules, linked to GO terms including Wnt signaling in immature testis, lipid metabolism, and cilia assembly in mature testis, ribosome biogenesis and DNA repair in the ovary, and hormone activity in pituitary. We identified new copies of known genes, such as gh1, pou3f2, and ier5 associated with the regulation of gonadal and pituitary functions. Some lncRNAs and their nearest genes showed correlated expression within modules, suggesting potential regulatory roles. Candidate lincRNAs indicated cis-acting regulatory potential on genes like tnfrsf11b and fgl1, which are implicated in immune privilege during gonadal development and sperm quality control. ConclusionsOur study provides a comprehensive transcriptomic analysis of Atlantic salmon gonad and pituitary tissues, significantly improving the functional annotation of the Atlantic salmon genome. These findings reveal key regulatory pathways and novel molecular players involved in sexual maturation, particularly in the testis. Importantly, our study highlights the regulatory potential of lncRNAs in reproductive biology and maturation age variation, advancing our understanding of the molecular mechanisms governing sexual maturation. They further unlock future gene expression analyses and regulatory network reconstruction for dissecting the roles of lncRNAs in Atlantic salmon life history variation.

genetics↗

bioRxiv2025

Testicular gene expression patterns suggest a heterochronic shift underlying vgll3-mediated maturation age variation in Atlantic salmon

Heterochrony, or shifts in developmental timing, drives phenotypic diversity within and between species and shapes life history traits that can be selected for in changing environments which in turn promotes population resilience. Despite its importance, the molecular basis of heterochrony remains largely unknown. Mutations in "heterochronic genes" that regulate these processes can induce stable timing shifts, impacting important life history traits like pubertal timing. Heterochronic shifts in gene transcription are often tissue-specific and in mammals, for example, the testis shows the most pronounced heterochrony across species, especially during spermatogenesis. Age at maturity is a key adaptive trait across species, with vgll3, a Hippo pathway co-factor, as a main determinant in Atlantic salmon. The roles of vgll3 in maturation timing, adiposity, and energy storage are evolutionarily conserved across fish and mammals. Recent studies in salmon show vgll3 alleles; early (E) and late (L), affect reproductive gene expression, reinforcing its role in regulating developmental timing. This study examines whether vgll3 influences testicular heterochrony in Atlantic salmon by analyzing Hippo pathway-related gene expression in E and L genotypes. We observed heterochronic divergence in Hippo pathway gene transcription, indicating accelerated spermatogenesis-linked changes in the testes of vgll3*EE individuals. Since maturation in Atlantic salmon is closely tied to environmental changes, and the Hippo pathway acts as an environmental sensor, these findings suggest that Hippo-vgll3 shifts may also respond to environmental signals. This positions vgll3 as a heterochronic gene which is potentially affected by environmental changes (heterokairic), making it an ideal target for studying ecological adaptation linked to heterochrony.

developmental biology↗

bioRxiv2025

Density-dependent expression of epitranscriptomic, stress, and appetite regulating genes in Atlantic salmon

Intraspecific competition due to e.g., density, has substantial influence on fitness dynamics and life histories, but the underlying physiological mechanisms are often complex, and the molecular basis unclear. Further, designing laboratory experiments to measure physiological responses that reflect natural conditions is challenging. Here, we reared Atlantic salmon juveniles in semi-wild conditions in two naturally occurring densities to investigate the molecular mechanism of density-related changes in the hypothalamus, a key brain region regulating stress and energy homeostasis. We measured density-dependent changes in the expression of 12 genes involved in appetite and stress regulation, and 16 genes involved in post-transcriptional regulation of gene expression via m6A RNA methylation. This gene set includes paralog pairs, to account for potential functional divergence associated with salmonid genome duplication. We also quantified genotype-environment interactions between density and two major life-history loci, vgll3 and six6. We found significant density-related differences in the expression of genes coding for corticotropin-releasing factors, appetite stimulators and inhibitors, and m6A RNA methylation actors. Moreover, a paralogue of an appetite inhibitor showed a density-dependent pattern that was the opposite of what was expected. Six6 locus was also associated with changes in the expression of epitranscriptomic markers, including two writers and one eraser. Our results highlight that individuals response to density in natural conditions is shaped by a complex interplay between stress, appetite and epitranscriptomic pathways in the hypothalamus. In addition, the functional divergence of paralogs indicates a potential role of genome duplication shaping such a response. We emphasize the value of integrating different physiological responses at the molecular level to better understand ecological processes affected by environmental change.

molecular biology↗

bioRxiv2025

High genetic diversity and no detectable founder effects following a rapid range expansion of a long-distance migrant (Acrocephalus scirpaceus)

Many species are currently experiencing range shifts in response to changing environmental conditions, but with potentially serious genetic consequences. Repeated founder events and strong genetic drift are expected to erode genetic variation at the range front, reducing adaptive potential and slowing or even halting the expansion. However, the severity of these consequences for the more common and highly mobile species undergoing environment-driven range shifts (c.f. invasions) is less clear. Here we combined historical observations and contemporary movement data of the common reed warbler (Acrocephalus scirpaceus) with genomic evidence from across its European breeding range to (1) infer the origin and (2) quantify the genetic consequences of a recent and rapid northward range expansion. While there were no reductions in levels of nucleotide diversity or allelic richness, nor a signal of founder effect in the directionality index ({psi}), our combined dataset approach was able to infer an expansion origin from the southwest. Furthermore, we found that private allelic richness retained a slight but significant linear decline along the colonisation route. These results suggest that high dispersal capabilities can allow even philopatric species to avoid the loss of genetic diversity during rapid range expansions. Nevertheless, if multiple lines of evidence enable identification of an expansion pathway, we may still detect genetic signals of expansion.

evolutionary biology↗

bioRxiv2024

Food quality and vgll3 genotype influence reproductive traits in female Atlantic salmon

Age at maturity is an important factor contributing to life-history diversity. In Atlantic salmon, this trait often shows sex-specific variation, but female salmon are seldom included in experimental studies of maturation. As a result, there is a gap in our knowledge of how different genetic and environmental factors affect female maturation. Using a 4-year common-garden experiment, we assessed the influence of diet (low-fat vs. control) and vgll3 (a candidate gene in a genomic region known to influence age at maturity in Atlantic salmon) on maturation and related phenotypic traits of female Atlantic salmon from two 2nd-generation hatchery populations. We found the early-maturation-associated vgll3*E allele to be associated with higher probability of maturation. Heritability of maturation was estimated to be 0.295 with vgll3s contribution to phenotypic variance being [~]2%. In addition, both body size and body condition measured in the spring prior to spawning influenced maturation. Body condition, in turn, was influenced by population and diet. The northern Oulu population and the low-fat diet were associated with lower body condition compared to the southern Neva population and the control diet. Moreover, there was an interaction between population and diet on body condition, suggesting that populations may respond differently to nutrient availability. These results broaden our understanding of the processes underlying maturation and demonstrate that genes and environment interact to shape age at maturity in female Atlantic salmon.

evolutionary biology↗

bioRxiv2024

Large effect life-history genomic regions are associated with functional morphological traits in Atlantic salmon

Understanding pleiotropic architectures of phenotypes is instrumental for identifying the functional basis of adaptive genetic variation in the wild. Life-history variation may have a morphological basis that mediates resource acquisition allocation pathways, but identifying the underlying genetic basis of such traits is challenging. Using Atlantic salmon juveniles reared in common garden conditions, we test if two life-history associated loci in Atlantic salmon, six6 and vgll3, are also associated with functional morphological traits. These loci had previously shown to exhibit strong signals of adaptation and are highly correlated with sea age at maturity. We show that genetic variation at the vgll3 locus is linked to variation in morphological traits that underlie swimming performance, along a trade-off axis between efficient cruising and maneuvering, while the genetic variation at the six6 locus was linked to variation in body-head proportions suggesting the potential functional importance of these traits for resource acquisition efficiency. However, the direction of changes in morphological traits associated with late-vs. early-maturing alleles was not always consistent with the expected direction of an effect to maturation timing. Our results reveal a complex morphological landscape associated with the genetic variation in these loci, possibly as a result of pleiotropy or linkage across these genomic regions.

ecology↗

bioRxiv2024

Hippo-vgll3 signaling may contribute to sex differences in Atlantic salmon maturation age via contrasting adipose dynamics

Sexual maturation in Atlantic salmon entails a transition in energy utilization, governed in part by genes and environmental stimuli in sex-specific manner. Salmon males require less energy, in the form of adiposity, to mature compared to females and typically mature younger. Maturation age is also influenced in a sex-dependent fashion by the vgll3 genotype (vestigial-like 3), a co-factor in the Hippo pathway. The underlying molecular processes of sex-dependent maturation age, and how they interplay with adiposity and vgll3 genotypes, have remained unknown. To elucidate the molecular mechanisms underlying sex- and genotype-specific maturation differences, we investigated the association of early (E) and late (L) maturation vgll3 alleles and the transcriptional expression of > 330 genes involved in the regulation of the Hippo pathway and sexual maturation, and related to molecular signals in brain, adipose tissue, and gonads. The strongest effect of vgll3 genotype was observed in adipose tissue for females and in brain for males, highlighting a sex-specific expression difference in the main association of vgll3 genotype. Genes related to ovarian development showed increased expression in vgll3*EE compared to vgll3*LL females. Additionally, vgll3*EE females compared to vgll3*EE males exhibited reduced markers of pre-adipocyte differentiation and lipolysis yet enhanced expression of genes related to adipocyte maturation and lipid storage. Brain gene expression further showed sex-specific expression signals for genes related to hormones and lipids, as well as tight junction assembly. Overall, these sex-specific patterns point towards a greater lipid storage and slower energy utilization in females compared to males. These results suggest that Hippo-dependent mechanisms may be important mediators of sex differences in maturation age in salmon.

genetics↗

bioRxiv2024

A single nucleotide polymorphism genotyping panel for efficient genetic stock identification of the Teno river Atlantic salmon (Salmo salar) population complex

A new single nucleotide polymorphism (SNP) panel for genetic stock identification in the Teno River Atlantic salmon fishery was developed, with a view to improving on an existing microsatellite panel. Twenty-two genetically differentiated reporting units were proposed based on population genetic analyses of 1212 individuals collected at 37 locations in the river and genotyped for > 33,000 genome-wide SNPs. A small subset of these SNPs was selected for GSI using an iterative process that considered their diversity and differentiation across reporting units. A genotyping-by-sequencing assay was developed to simultaneously genotype 180 of these GSI SNPs plus a sexing marker. This new SNP panel showed comparative GSI power to the microsatellite panel, with anticipated improvements in terms of cost, speed, and robustness and transferability across laboratories and genotyping platforms. Mixed stock analysis of the 2018 Teno River salmon catch using the new panel inferred all 22 reporting units to contribute to the fishery. Estimated catch proportions positively scaled with an independent estimate of reporting unit productivity: target spawning female biomass. This demonstrates the usefulness and efficiency of the 180 SNP panel for Atlantic salmon GSI in the Teno River system. If conducted on a regular basis, GSI can enable fine-tuning of management strategies to promote sustainable fishing.

evolutionary biology↗

bioRxiv2024

Sex-, development-, and nutrition-dependent expression of a major age-at-maturity gene in Atlantic salmon

Sexual maturation is a key process in the life history of an organism and is influenced by both genetic and environmental factors. In Atlantic salmon (Salmo salar), alternative alleles at the gene vgll3 have been found to associate with a large proportion of the variation in maturation age, yet the molecular and physiological mechanisms of this association are still largely unknown. Here, we investigated the mechanisms by which genetic variation in this major age-at-maturity gene translated into phenotypic variation. We established a time series of gonadal vgll3 mRNA expression in male and female Atlantic salmon in a common garden setting, starting at the prepubertal stage and spanning multiple spawning seasons. We found that vgll3 mRNA expression is reduced in early-maturing males and females. However, for the second spawning season, vgll3 expression increased with gonadal development in males, but eventually decreased in females. Expression of vgll3 had context-dependent correlations with expression of amh and lhr. We also found signs of reduced testicular vgll3 expression in a low-fat feed treatment. By significantly widening the scope of our knowledge on temporal vgll3 expression dynamics, our results exemplify that major-effect genes may use different pathways in sexes but achieve similar outcomes.

genetics↗

bioRxiv2024

A salmon fish model reveals genetic signals in brain associated with early maturation

Emerging evidence suggests a link between adiposity and early maturation, potentially impacting hormonal signaling pathways governing puberty timing. Fish models have proven invaluable in studying these processes, given their genetic and physiological similarities to humans. In Atlantic salmon, in addition to being linked with environmental shifts and lipid reserves, the timing of sexual maturation also has a strong genetic basis. A gene encoding a co-factor of Hippo pathway, vgll3, is a major determinant of maturation timing in salmon, and the same gene was found to be associated with maturation timing in humans. Intriguingly, vgll3 also inhibits adipogenesis in mice. Recent studies in salmon revealed correlations between vgll3 genotypes and reproductive axis gene expression, possibly modulated through the Hippo signaling pathway. The Hippo pathway is known for its role in sexual maturation and adipogenesis and responds to environmental cues such as dietary fat and temperature. In this study, we employed a custom gene expression panel in male Atlantic salmon with different vgll3 early (E) and late (L) maturation genotypes testing components of this pathway in brain at immature and mature stages. We found increased brain expression of a major Hippo pathway kinase (lats1b) and melanocortin receptor encoding genes (mc4ra and mc4rc) in individuals with early (E) maturation genotypes of vgll3 before maturation development of testes. Moreover, we found components and interacting partners of Hippo pathway showing differential expression in brain of individuals with early (E) and late (L) vgll3 genotypes prior to maturation. This could indicate extensive and complex roles of Hippo pathway in brain processes required for preparing for [the onset of] maturation at upstream of reproductive axis. This study elucidates molecular mechanisms underpinning early maturation, and for the first time in fish, offering insights into detecting it at molecular level in brain before visible gonadal changes occur.

genetics↗

bioRxiv2024

A complex mechanism translating variation of a simple genetic architecture into alternative life-histories

Linking genes to traits is a central goal in biology. Despite progress in discovering genes associated with trait differences, a poor understanding of the functional mechanisms underlying genetic associations leaves us critically far from connecting genetic and phenotypic variation. This knowledge-gap is particularly large in multifaceted phenotypes of ecological relevance such as life-history traits. Using a multiomic dissection of the genotype-phenotype association in a large-effect maturation age gene - the transcription cofactor vestigial-like 3 (vgll3) - in Atlantic salmon (Salmo salar), we show that vgll3 mediates concerted changes of distinct molecular phenotypes associated with puberty in male gonads. Vgll3 genotype conferring early maturity upregulates key genes controlling androgen production, cellular energy and adiposity, and TGF-{beta} signaling, among others, thereby increasing the likelihood of earlier pubertal initiation. Genotype-dependent developmental trajectories are produced through VGLL3 interaction with distinct transcription factors, thus coordinating differential activation of regulatory pathways. These results reveal a genetically simple, yet functionally complex, architecture underlying alternative life-histories where variation in a single major effect gene produces pleiotropic variation in a spectrum of cellular traits. Our results further suggest that evolution in correlated phenotypes such as exemplified by alternative life history strategies may be mediated by a surprisingly simple genetic architecture.

evolutionary biology↗

bioRxiv2023

Gene co-expression patterns in Atlantic salmon adipose tissue provide a molecular link between seasonal changes, energy balance and age at maturity

Sexual maturation in many fishes requires a major physiological change that involves a rapid transition between energy storage and usage. In Atlantic salmon, this transition for the initiation of maturation is tightly controlled by seasonality and requires a high-energy status. Lipid metabolism is at the heart of this transition since lipids are the main energy storing molecules. The balance between lipogenesis (lipid accumulation) and lipolysis (lipid use) determines energy status transitions. A genomic region containing a transcription co-factor of the Hippo pathway, vgll3, is the main determinant of maturation timing in Atlantic salmon. Interestingly, vgll3 acts as an inhibitor of adipogenesis in mice and its genotypes are potentially associated with seasonal heterochrony in lipid storage and usage in juvenile Atlantic salmon. Here, we explored changes in expression of more than 300 genes directly involved in the processes of adipogenesis, lipogenesis and lipolysis, as well as the Hippo pathway in the adipose tissue of immature and mature Atlantic salmon with distinct vgll3 genotypes. We found molecular evidence consistent with a scenario in which immature males exhibiting vgll3 genotype specific seasonal direction of change in their lipid profiles. We also identified components of the Hippo signaling pathway as potential major drivers of vgll3 genotype specific differences in adipose tissue gene expression. This study demonstrates the importance of adipose gene expression patterns for directly linking environmental changes with energy balance and age at maturity through genetic factors bridging lipid metabolism, seasonality and sexual maturation.

physiology↗

bioRxiv2023

Loci associated with migration, maturation and appetite control are linked with signals of fine-scale local selection in a large Atlantic salmon population

Insights into the genetic basis of local adaptation and drivers of population differentiation improve our understanding of evolution and the maintenance of biological diversity. Characterising adaptively important genetic variation also allows more efficient planning of conservation and management actions. We used a genome-wide SNP array to analyse the genetic population structure of a large Atlantic salmon (Salmo salar) population in the interconnected Tornio/Torne and Kalix River system of the Baltic Sea basin, and to identify genomic signatures of fine-scale selection within it. We identified signals of selection and genotype-environment associations (GEA) especially on chromosome (Chr) 9, including on a haploblock containing the six6 gene and other loci that have been earlier suggested to be adaptively important in salmonids. We also detected signals of selection in genome regions including other genes of ecological relevance, such as two known appetite-controlling genes in the melanocortin system (pomca on Chr 9 and mc4r on Chr 14), and the maturation-associated gene taar13c-like (on Chr 21). Variation in these and other identified candidate genes may potentially reflect differential selective pressures experienced by salmon from different parts of the large river system, regarding traits related to e.g. vision, feeding and growth, age at maturity and/or migratory timing. This indicates a need for management strategies to consider ecologically important genomic regions such as these, in order to protect adaptive genetic diversity in wild salmon populations.

evolutionary biology↗

bioRxiv2023

Seasonal and genetic effects on lipid profiles of juvenile Atlantic salmon

Seasonality can influence many physiological traits requiring optimal energetic capacity for life-history stage transitions. In Atlantic salmon, high-energy status is essential for the initiation of maturation. Atlantic salmon lipid reserves are predominantly found in the viscera and myosepta in the muscle while the liver is essential for maintaining lipid metabolism. A genomic study found a region including a transcription co-factor-coding gene, vgll3, linked to Atlantic salmon maturation timing, which acts as an inhibitor of adipogenesis in mice, and mediates maturation via condition factor in Atlantic salmon. Here we investigate the influence of season and vgll3 genotypes associating with early (EE) and late (LL) maturation on lipid profiles in the muscle and liver in juvenile Atlantic salmon. We reared Atlantic salmon for two years until the occurrence of sexually mature males and sampled muscle and liver at two time points: spring and autumn of the second year. We found no seasonal or genotype effect in lipid profiles in muscle of immature males and females. However, in the liver we did detect a triacylglycerol (TG) enrichment and a genotype specific direction of change in membrane lipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), from spring to autumn. Specifically, from spring to autumn membrane lipid concentrations increased in vgll3*EE individuals and decreased in vgll3*LL individuals. This could be explained with two possible scenarios 1) a seasonally more stable capacity of endoplasmic reticulum (ER) functions in vgll3*EE individuals compared to vgll3*LL individuals or 2) vgll3*LL individuals storing larger lipid droplets from spring to autumn in the liver compared to vgll3*EE individuals at the expense of ER capacity. This genotype specific seasonal direction of change in membrane lipid concentrations provides more indirect evidence that a mechanism linking vgll3 with lipid metabolism and storage exists. HighlightsO_LISeasonal lipid species profile separation in muscle and liver in juvenile Atlantic salmon C_LIO_LIGenotype specific direction of change of membrane lipids from spring to autumn C_LIO_LIIndirect evidence that a mechanism linking vgll3 with lipid metabolism and storage exists C_LI

evolutionary biology↗