Polygenic selection to a changing optimum under self–fertilisation

Abstract

AbstractMany traits are polygenic, affected by multiple genetic variants throughout the genome. Selection acting on these traits involves co–ordinated allele– frequency changes at these underlying variants, and this process has been extensively studied in random–mating populations. Yet many species self– fertilise to some degree, which incurs changes to genetic diversity, recombination and genome segregation. These factors cumulatively influence how polygenic selection is realised in nature. Here, we use simulations to investigate to what extent self–fertilisation affects polygenic adaptation to a new environment. We find that self–fertilisation can incur a fitness advantage through purging maladaptive genotypes. While the degree of self– fertilisation has little influence on how quickly a population adapts to a new optimum, those with the highest long–term fitness tended to have high levels of selfing (at least 90%). Very high levels of self–fertilisation (99% and above) causes fixation of variants with compensatory effects in elevated linkage disequilibrium across the genome. Conversely, if mutations are pleiotropic then only a few major–effect variants fix along with many neutral hitchhikers, with a transient increase in linkage disequilibrium. If deleterious mutations are also present then linkage–block formation is disrupted in highly–selfing species, with fewer mutations contributing to adaptation and less chance of high–linkage genomes persisting over time. We also show how these outcomes differ in outcrossing populations with rescaled mutation and recombination rates, demonstrating that elevated homozygosity also influences the selection response. These results show potential advantages to self–fertilisation when adapting to a new environment, and how the mating system affects the genetic composition of polygenic selection.Website for simulation codehttps://github.com/MattHartfield/Polygenic-Selfing