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

Abstract

Rapid evolution through small shifts in allele frequencies at thousands of loci is a long-standing neo-Darwinian prediction but is hard to characterize in the wild. European ash tree (<i>Fraxinus excelsior</i>) populations have recently come under strong selection by the invasive fungal pathogen <i>Hymenoscyphus fraxineus</i>. Using genomic prediction models based on field trial phenotypes and 7985 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 microevolutionary adaptive change over a single generation in the wild.