Mutation bias is a key predictor of adaptation rate

Mutation bias reversal in Escherichia coli increases adaptation rate by about 5% and halves variation in adaptation rates across replicate populations.

• Why it matters: Mutation bias is linked to how adaptation’s genetic basis and fitness effects are distributed, but it was unclear whether bias shifts are strong enough to change adaptive outcomes.
• What they did: The study tested bias reversal in Escherichia coli, showing that adaptation slows as replicate populations diverge while the beneficial-mutation-supply effect strengthens over time.
• The result: Bias reversal increases beneficial mutation supply, yielding ~2–3 times as many beneficial mutations as strains with reinforced bias, shaping accumulated genomic mutation types and improving prediction of evolution.