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Kemppainen, P. M.

Publications and source records attributed to Kemppainen, P. M..

2 recordsLinked to original sources

Linkage disequilibrium scaling improves robustness and power to detect genomic regions under selection.

Understanding the genetic basis of adaptive evolution is central to predicting how populations respond to environmental change. Genome scans and genotype-environment association methods are widely used to detect loci under selection, but because they often ignore correlations among loci (linkage disequilibrium, LD), their power decreases with increasing genetic structuring and demographic complexity. While LD contains valuable information about selection and can reduce dimensionality by summarizing signal across correlated markers, existing LD-based approaches are computationally demanding and rely on ad hoc threshold choices. Here, we introduce a novel LD-scaled association statistic, F ', which incorporates local LD directly into genotype-environment association tests using a fast permutation-based quantile transformation. Using forward-in-time simulations with known ground truth, we evaluate F ' across two widely used methods--latent factor mixed models (LFMM) and EMMAX--and assess performance at the level of outlier regions rather than individual SNPs. We further integrate uncertainty in parameter choice and inference method using a consistency-based framework. Across simulations, LD-scaling and joint inference substantially increased detection power and robust-ness, yielding up to an order-of-magnitude improvement under strong genetic structuring and nearly doubling performance on average across scenarios. Applying this framework to three- and nine-spined stickleback datasets, we recover well-established genomic regions associated with parallel marine-freshwater adaptation with markedly reduced background noise compared to standard analyses. Together, our results demonstrate that explicitly leveraging LD structure and integrating over analytical uncertainty provides a powerful and computationally efficient extension to genome scans for selection, improving robustness and interpretability in both simulated and empirical settings.

evolutionary biology↗

Convergent genetic architecture underlies parallel pelvic reduction in genetically highly structured stickleback species

Repeated and independent adaptation to specific environmental conditions from standing genetic variation is common. However, if genetic variation is limited, the evolution of similar locally adapted traits may be restricted to genetically different and potentially less optimal solutions or prevented from happening altogether. Using a quantitative trait locus (QTL) mapping approach, we identified the genomic regions responsible for the repeated pelvic reduction (PR) in three crosses between nine-spined stickleback populations expressing full and reduced pelvic structures. In one cross, PR mapped to linkage group 7 (LG7) containing the gene Pitx1, known to control pelvic reduction also in the three-spined stickleback. In the two other crosses, PR was polygenic and attributed to ten novel QTL, of which 90% were unique to specific crosses. When screening the genomes from 27 different populations for deletions in the Pitx1 regulatory element, these were only found in the population in which PR mapped to LG7, even though the morphological data indicated large effect QTL for PR in several other populations as well. Consistent with the available theory and simulations parameterised on empirical data, we hypothesise that the observed variability in genetic architecture of PR is due to heterogeneity in the spatial distribution of standing genetic variation caused by >2x stronger population structuring among freshwater populations and >10x stronger genetic isolation by distance in the sea in nine-spined sticklebacks as compared to three-spined sticklebacks.

evolutionary biology↗