Genome-wide signatures of synergistic epistasis during parallel adaptation in a Baltic Sea copepod

The role of epistasis in adaptive evolution has remained an unresolved problem dating back to the Evolutionary Synthesis. This role is now being revisited due to its relevance for polygenic adaptation. In the absence of epistasis, polygenic adaptation is predicted to result in non-parallel evolution, because repeated selection could act on subsets of effectively redundant alleles. However, positive epistatic interactions among adaptive alleles would make the alleles non-redundant and selection for particular allelic combinations could drive parallel evolution. The inability to address this fundamental question might arise from traditional approaches lacking the power to capture the genomic architecture and dynamics of polygenic adaptation. To address this problem, we employed a replicated and controlled evolution experiment using the copepod Eurytemora affinis to elucidate the evolutionary response architecture to rapid salinity decline, a predicted consequence of global climate change ...