Fine-scale contemporary recombination variation and its fitness consequences in adaptively diverging stickleback fish [ATAC-Seq]

Despite deep evolutionary conservation, recombination varies greatly across the genome, among individuals, sexes and populations and can be a major evolutionary force in the wild. Yet this variation in recombination and its impact on adaptively diverging populations is not well understood. To elucidate the nature and potential consequences of recombination rate variation, we characterized fine-scale recombination landscapes by combining pedigrees, functional genomics and field fitness measurements in an adaptively divergent pair of marine and freshwater threespine stickleback populations from River Tyne, Scotland. Through whole-genome sequencing of large nuclear families, we identified the genomic location of almost 50,000 crossovers and built recombination maps for 36 marine, freshwater, and hybrid individuals at 3.8 kilobase resolution. Using these maps, we quantified the factors driving variation in recombination rate: we find strong heterochiasmy between sexes (68% of the variation) but also differences among ecotypes (21.8%). Hybrids show evidence of significant recombination suppression, both in overall map length and in individual loci. We further tested and found reduced recombination rates both within single marine–freshwater adaptive loci and between loci on the same chromosome, suggestive of selection on linked ‘cassettes’. We tested theory supporting the evolution of linked selection using temporal sampling along a natural hybrid zone, and found that recombinants with shuffled alleles across loci show traits associated with reduced fitness. Our results support predictions that divergence in cis-acting recombination modifiers whose mechanisms are disrupted in hybrids, may have an important role to play in the maintenance of differences among adaptively diverging populations. This GEO data deposit is part of a multipart study that includes functional genomic data related to meiosis in stickleback fish as described in Venu et al 2024. This particular data series includes an ATACseq dataset of chromatin accessibility in stickleback primary spermatocytes. For each ATAC-seq library, the testes of three males were pooled. A control library of naked DNA was also prepared for each pool. Three marine ecotype libraries and three freshwater ecotype libraries were analyzed.