title: Fluctuating Selection in the Moran.
abstract: Contrary to classical population genetics theory, experiments demonstrate that fluctuating selection can protect a haploid polymorphism in the absence of frequency dependent effects on fitness. Using forward simulations with the Moran model, we confirm our analytical results showing that a fluctuating selection regime, with a mean selection coefficient of zero, promotes polymorphism. We find that increases in heterozygosity over neutral expectations are especially pronounced when fluctuations are rapid, mutation is weak, the population size is large, and the variance in selection is big. Lowering the frequency of fluctuations makes selection more directional, and so heterozygosity declines. We also show that fluctuating selection raisesdn/dsratios for polymorphism, not only by sweeping selected alleles into the population, but also by purging the neutral variants of selected alleles as they undergo repeated bottlenecks. Our analysis shows that randomly fluctuating selection increases the rate of evolution by increasing the probability of fixation. The impact is especially noticeable when the selection is strong and mutation is weak. Simulations show the increase in the rate of evolution declines as the rate of new mutations entering the population increases, an effect attributable to clonal interference. Intriguingly, fluctuating selection increases thedn/dsratios for divergence more than for polymorphism, a pattern commonly seen in comparative genomics. Our model, which extends the classical neutral model of molecular evolution by incorporating random fluctuations in selection, accommodates a wide variety of observations, both neutral and selected, with economy.
authors.affiliation: State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, People's Republic of China deanx024@umn.edu.|Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, Minnesota 55108.|BioTechnology Institute, University of Minnesota, St. Paul, Minnesota 55108.
authors.forename: Antony M
authors.initials: AM
authors.lastname: Dean
authors.affiliation: Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, Minnesota 55108.
authors.forename: Clarence
authors.initials: C
authors.lastname: Lehman
authors.affiliation: Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, Minnesota 55108.|BioTechnology Institute, University of Minnesota, St. Paul, Minnesota 55108.
authors.forename: Xiao
authors.initials: X
authors.lastname: Yi
mesh_terms: D019143:Evolution, Molecular; D005787:Gene Frequency; D006238:Haploidy; D006579:Heterozygote; D006720:Homozygote; D008957:Models, Genetic; D011110:Polymorphism, Genetic; D012641:Selection, Genetic
keywords: Moran model; fluctuating selection; heterozygosity; rate of evolution