Biology subjects

Bolstad, G. H.

Publications and source records attributed to Bolstad, G. H..

6 recordsLinked to original sources

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↗

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

Bayesian marker-based principal component ridgeregression - a flexible multipurpose framework forquantitative genetics in wild study systems

As larger genomic data sets become available for wild study populations, the need for flexible and efficient methods to estimate and predict quantitative genetic parameters, such as the adaptive potential and measures for genetic change, increases. Animal breeders have produced a wealth of methods, but wild study systems often face challenges due to larger effective population sizes, environmental heterogeneity and higher spatio-temporal variation. Here we adapt methods previously used for genomic prediction in animal breeding to the needs of wild study systems. The core idea is to approximate the breeding values as a linear combination of principal components (PCs), where the PC effects are shrunk with Bayesian ridge regression. Thanks to efficient implementation in a Bayesian framework using integrated nested Laplace approximations (INLA), it is possible to handle models that include several fixed and random effects in addition to the breeding values. Applications to a Norwegian house sparrow meta-population, as well as simulations, show that this method efficiently estimates the additive genetic variance and accurately predicts the breeding values. A major benefit of this modeling framework is computational efficiency at large sample sizes. The method therefore suits both current and future needs to analyze genomic data from wild study systems.

evolutionary biology↗

bioRxiv2022

Genetic stock identification reveals greater use of an oceanic feeding ground around the Faroe Islands by multi-sea winter Atlantic salmon.

There is a general paucity of knowledge regards spatial variation in marine resource use for many taxa, even those of high socio-economic importance such as Atlantic salmon. While it is known that the oceans around the Faroe Islands support a salmon feeding ground, the relative use of this feeding ground by different age classes across different stocks remains largely unexplored. Using a combination of genetic stock assignment and run-reconstruction models, we observed a consistent pattern whereby the proportion of multi-sea winter (MSW) salmon for a given reporting group was substantially greater around the Faroes than the MSW proportion for that reporting groups among the prefisheries abundance. Surprisingly, MSW fish from Ireland and UK were as likely to occur around the Faroes as were MSW fish from more north-eastern regions such as the Teno river and the Barents and White Seas. MSW fish from Southern Norway were the most likely to be caught at the Faroes. While 1SW salmon from Ireland and UK as well as from Southern Norway occurred at similar rates around the Faroes, 1SW fish from more north-eastern reporting groups were nearly entirely absent from the same feeding ground. In combination with previous studies that examine the marine distribution of Atlantic salmon, our results strongly indicate that the oceans around the Faroes play host to a predominantly MSW salmon feeding ground and that use of this resource varies both within the age classes of a given stock as well as between different stocks. Furthermore, these results suggest that MSW fish from certain stocks might preferentially undertake migrations to the Faroes. Variation in spatial resource use may help to buffer salmon stocks against localised negative changes in marine conditions.

ecology↗

bioRxiv2021

Dissecting the loci underlying maturation timing in Atlantic salmon using haplotype and multi-SNP based association methods

Resolving the genetic architecture of fitness-related traits is key to understanding the evolution and maintenance of fitness variation. However, well-characterized genetic architectures of such traits in wild populations remain uncommon. In this study, we used haplotype-based and multi-SNP Bayesian association methods with sequencing data for 313 individuals from wild populations to further characterize known candidate regions for sea age at maturation in Atlantic salmon (Salmo salar). We detected an association at five loci (on chromosomes ssa06, ssa09, ssa21, and ssa25) out of 116 candidates previously identified in an aquaculture strain with maturation timing in wild Atlantic salmon. We found that at each of these five loci, variation explained by the locus was predominantly driven by a single SNP suggesting the genetic architecture of Atlantic salmon maturation includes multiple loci with simple, non-clustered alleles. This highlights the diversity of genetic architectures that can exist for fitness-related traits. Furthermore, this study provides a useful multi-SNP framework for future work using sequencing data to characterize genetic variation underlying phenotypes in wild populations.

evolutionary biology↗

bioRxiv2020

Fly wing evolutionary rate is a near-isometric function of mutational variation

If there is abundant mutational and standing genetic variation, most expect that the rate of evolution would be driven primarily by natural selection, and potentially be independent of current variability or variation. Contrary to this expectation, we (H17: Houle et al. 2017 Nature 548:447) found surprisingly strong scaling relationships with slopes near one between mutational variance, standing genetic variance and macro-evolutionary rate in Drosophilid wing traits. Jiang and Zhang (J&Z20: 2020 Evolution https://doi.org/10.1111/evo.14076) have challenged these results and our interpretation of them. J&Z20 showed that the method used in H17 to estimate the scaling relationship between variation at different biological levels is uninformative. Using an alternative method, they estimated that the scaling relationship has a slope substantially less than one, and propose a variant of our neutral subset hypothesis to explain this. Here we use simulations to confirm J&Z20s finding that the H17 method for estimating scaling of variances is uninformative. The simulations also show their alternative method for estimating scaling is likely to be seriously biased towards lower scaling relationships. We propose and verify an alternative approach to calculating scaling relationships based on independently estimated variance matrices, which we call the Q method. Simulations and reanalyses of the Drosophilid data set using the Q method suggests that our original estimates of the scaling relationship were close to the true value. We propose an analytical version of the neutral subset model, and show that it can indeed explain any scaling slope by varying assumptions about the pattern of pleiotropy. We continue to regard neutral subset models as implausible for wing shape in Drosophilids due to the likelihood that wing shape is subject to direct selection. Hybrid models in which pleiotropy reduces the available genetic and mutational variation, and a combination of selection and drift controls the change in species means seem more biologically promising.

evolutionary biology↗