Adaptation dynamics between copy-number and point mutations.

Area of Science:

• Evolutionary biology
• Microbial genetics

Background:

• Gene duplication and divergence are key drivers of evolutionary novelty.
• Early dynamics of mutations following gene duplication are poorly understood.
• Microbial adaptation often involves gene copy-number expansion for increased expression.

Purpose of the Study:

• To investigate the early adaptive dynamics of copy-number and point mutations in real time.
• To differentiate the roles of these mutation types under varying selective pressures.
• To characterize the interplay between mutation types during adaptation.

Main Methods:

• Utilized a synthetic genetic reporter system in *Escherichia coli* to distinguish mutation types.
• Observed adaptive dynamics in real time under controlled laboratory conditions.
• Analyzed mutation frequencies and adaptive trajectories under different gene expression demands.

Main Results:

• Identified two distinct adaptive routes based on functional improvement needs.
• In high gene expression demand, copy-number and point mutations occurred concurrently.
• Under low gene expression demand, these mutation types were mutually exclusive, with copy-number mutations dominating adaptation (amplification hindrance).

Conclusions:

• Copy-number mutations provide a rapid, albeit transient, adaptation mechanism.
• Amplification hindrance by copy-number mutations can limit sequence divergence.
• High reversal rates and pleiotropic costs associated with copy-number mutations impact long-term evolutionary trajectories.