Polygenic adaptation under recurrent changes in environment
Authors: Jiarun Chen; Guy Sella
Affiliation: Columbia University
Keywords: Theory & Method Development
Polygenic adaptation is expected to be ubiquitous, yet remains poorly studied. Previous work modeled this process for a quantitative, highly polygenic trait that experiences a sudden shift in the fitness optimum, and found that the long-term adaptive response arises from a slightly greater number of fixations of alleles whose effects are aligned with the shift than that of fixations of alleles with opposing effects. These fixations occur over a time scale of 2Ne, where Neis the effective population size. However, the fitness optimum plausibly changes repeatedly over this time scale, suggesting that recurrent shifts in the fitness optimum should probably be more biologically realistic. Here we model a quantitative, highly polygenic trait that experiences recurrent shifts in the fitness optimum, where the waiting time between shifts is exponentially distributed, the direction of each shift is random, i.e., with probability 0.5 increasing and decreasing the fitness optimum, respectively, and the magnitude of each shift follows some distribution. In particular, we ask how the fixation probability and allele frequency distribution depends on the allelic effects on the trait, and on the frequency and magnitude of changes to the environment, using analytical methods and simulations. We anticipate our results to have important implications in the genetic basis of polygenic adaptation in humans and other species, and in enduring questions about the rate of molecular evolution and levels of genetic diversity.