Rapid adaptation of a polygenic trait after a sudden environmental shift

TL;DR

This paper models the rapid genetic and phenotypic changes in populations after sudden environmental shifts, revealing the dynamics of polygenic adaptation and the conditions for detectable genomic signatures.

Contribution

It provides explicit analytical expressions for the short-term response of polygenic traits to environmental changes, enhancing understanding of rapid adaptation mechanisms.

Findings

Small effect sizes lead to subtle allele frequency changes

Large effect sizes can cause selective sweeps

Short-term adaptation involves synergistic allele frequency shifts

Abstract

Although a number of studies have shown that natural and laboratory populations initially well-adapted to their environment can evolve rapidly when conditions suddenly change, the dynamics of rapid adaptation are not well understood. Here a population genetic model of polygenic selection is analyzed to describe the short-term response of a quantitative trait after a sudden shift of the phenotypic optimum. We provide explicit analytical expressions for the time scales over which the trait mean approaches the new optimum. We find that when the effect sizes are small relative to a scaled mutation rate, the genomic signatures of polygenic selection are small to moderate allele frequency changes that occur in the short-term phase in a synergistic fashion. In contrast, selective sweeps, i.e., dramatic changes in the allele frequency may occur provided the size of the effect is sufficiently large. Applications of our theoretical results to the relationship between QTL and selective sweep mapping and to tests of fast polygenic adaptation are discussed.