Rapid polygenic adaptation in a wild population of ash trees under a novel fungal epidemic

Abstract

Rapid evolution via small shifts in allele frequencies at thousands of loci are a long- standing neo-Darwinian prediction but are hard to characterize in the wild. European ash tree (Fraxinus excelsior) populations have recently come under strong selection by the invasive fungal pathogen Hymenoscyphus fraxineus. Using genomic prediction models based on field trial phenotypes and 7,985 loci, we show a shift in genomically estimated breeding values in an ancient woodland, between adult trees established before the epidemic started and juvenile trees established since. Using simulations, we estimate that natural selection has eliminated 31% of the juvenile population. Thus, we document a highly polygenic heritable micro-evolutionary adaptive change over a single generation in the wild. One-Sentence SummarySubtle changes at thousands of genomic locations in one generation allow woodland trees to respond to a new selective pressure