Fig. 1.

Experimental design. (A) Diverse founder populations were generated by mass sporulation of a cross between strains Y55 and SK1. (B) Asexual yeast populations were evolved for 1,000 generations in four environments: NaCl 0.75 M, EtOH 8%, LiAc 0.01 M, and LiAc 0.02 M. Shaded squares indicate selective media; white squares are the ancestral medium (SC). Replicate populations are indicated as separate arrows. Sampling time points for sequencing are indicated on the dotted arrow. One population of NaCl and LiAc 0.01 M, as well as the generation 1,000 of both LiAc treatments and of two populations of NaCl, were lost due to contamination. (C) Fitness assays using OD₆₀₀ after 24 h of growth were used to compare founders and evolved populations at six time points of evolution in selective and ancestral environments. Only a subset of all pairwise comparisons is shown. Assays were carried out at six time points (marked in bold on the left).