Recombination accelerates adaptation across genetic architectures and demographic histories

According to classic population genetics theory, recombination shapes the efficacy of natural selection. However, whether variation in recombination rate itself translates into meaningful differences in adaptive capacity remains poorly understood. Here, we used forward-time simulations to examine polygenic adaptation in populations colonizing novel environments. We varied recombination rate eightfold, modeled QTL effect size distributions using three gamma distributions, and compared constant and contracted population sizes. Across all conditions, higher recombination rates modestly accelerated adaptation, reducing the time to reach a new phenotypic optimum by 2-15%. The benefit was substantially greater in constant-size populations than in those that had experienced a contraction, but did not differ across genetic architectures. To understand the mechanism of this acceleration, we tracked linkage disequilibrium among adaptation-related QTL throughout adaptation. We found that across simulations, beneficial alleles were consistently in repulsion phase with one another and in coupling phase with deleterious alleles, both signatures of Hill-Robertson interference. Higher recombination attenuated both forms of interference, indicating that the benefit of recombination operated primarily through relieving interference among QTL. These results implicate interference among linked loci as the primary constraint on polygenic adaptation in this context, and demographic history as a critical modulator of the benefit of recombination.