janahn

• Nickel, Jana Helene; Laine, Jan Tapio & Foote, Andrew David (2026). Complex Patterns of Hitchhiking Mutation Load Among Stickleback Populations. Genome Biology and Evolution (GBE). 18(4). doi: 10.1093/gbe/evag088. Fulltekst i vitenarkiv Vis sammendrag

  Positive selection causes beneficial alleles to rise to high frequency in a population. This can cause linked genetic variation to “hitchhike,” and thereby also rise in frequency. This linked variation may include deleterious recessive alleles, previously neutrally harbored at low frequency and in heterozygous genotypes. Modeling studies have shown that local effective population size and reduced recombination rate should contribute to the probability of deleterious mutations being swept to high frequency by being linked to beneficial alleles in selective sweeps or selection on inversion karyotypes. Marine sticklebacks have repeatedly adapted to thousands of freshwater habitats that became available after the last ice age, resulting in the formation of distinct marine and freshwater ecotypes. Selection acts on ancient standing genetic variation present in marine populations, causing freshwater-adaptive alleles to increase rapidly over tens of generations. These genomic regions play a key role in the repeated freshwater adaptation of morphological, physiological, and behavioral traits, and evolve under strong selection. Thus, threespine stickleback is an ideal system for investigating the impact of hitchhiking mutation load. We estimate the mutation load in regions of low recombination, including inversions and the Eda haplotype. We find some evidence for increased accumulation of deleterious alleles in one inversion, while this is not the case for two other inversions. Inversions deviated from Hardy–Weinberg equilibrium in several populations due to an excess of homozygotes.

• Laine, Jan Tapio; Nickel, Jana Helene; Romundset, Anders & Foote, Andrew David (2025). Ancient stickleback genomes reveal the early stages of parallel adaptation. Evolution. ISSN 0014-3820. 79(11), s. 2446–2459. doi: 10.1093/evolut/qpaf164. Fulltekst i vitenarkiv Vis sammendrag

  The parallel evolution of traits and their underlying genetic basis is well studied; however, studies of the parallel chronology of adaptive genetic changes remain scarce. The probability of parallel genetic change should be increased by the clustering of adaptive alleles in regions of suppressed recombination, particularly for genes that have large fitness or phenotypic effects. The threespine stickleback is a model system for studying parallel evolution, here we present genomic data from nine subfossil stickleback bones dated to 14.8-0.7 KYR BP in age. Comparing the four highest coverage genomes, which represent different stages along the marine–freshwater divergence continuum, we find that the accumulation of freshwater ancestry is clustered rather than randomly distributed throughout the marine–freshwater divergent regions of the genome. We consistently find freshwater ancestry on chromosome IV at the early stages of freshwater adaptation. Regions of chromosome IV contain the greatest genetic differentiation between marine and freshwater ecotypes and among the highest density of quantitative trait loci. These include Ectodysplasin (EDA), a large-effect pleiotropic locus associated with defensive armor and variation in neurosensory and behavioral traits. Freshwater ancestry in the subfossils is also consistently found at inversions and X chromosome early in the adaptive process. Our findings add to emerging evidence that freshwater adaptation in threespine stickleback could have a staggered but predictable temporal dynamic.

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