Data from: Strength of selection potentiates distinct adaptive responses in an evolution experiment with outcrossing yeast

Selection intensity is expected to influence the magnitude and genetic
architecture of adaptive responses, yet it is rarely evaluated as a
standalone variable in experimental evolution studies. Here, we evolved
outcrossing populations of Saccharomyces cerevisiae for ~200 generations
across a spectrum of environmental stress from zero to moderate to high
ethanol exposure, to examine how genomic responses vary with stress
intensity. Across treatments, adaptation proceeded through many subtle
allele and haplotype frequency shifts rather than large changes at single
loci, consistent with a highly polygenic response. At loci associated with
ethanol adaptation, the high stress treatment led to larger allele
frequency changes compared to the moderate or no ethanol stress
treatments, with the genomic architecture of adaptation becoming
increasingly polygenic as selection intensity decreased. Moderate and high
stress conditions engaged partially distinct biological pathways,
indicating that selection intensity shapes both the magnitude and targets
of adaptive change. Within this stress continuum, we also observed
substantial, ongoing adaptation in control populations despite extensive
prior domestication. Many alleles associated with this adaptation showed
reduced or absent responses under ethanol stress, consistent with
antagonistic pleiotropy. Consequently, laboratory adaptation can represent
a major component of evolutionary change and may confound
treatment-specific inferences when not explicitly accounted for. Broadly,
our results demonstrate that selection intensity structures adaptive
responses in experimental evolution and that continued laboratory
adaptation remains an important force in these studies. Our findings
underscore the importance of clearly defined controls and careful
consideration of selection intensity when interpreting or comparing across
experimental evolution studies.