Populations adapt to fluctuating selection using derived and ancestral allelic diversity

Area of Science:

• Evolutionary biology
• Genetics
• Microbiology

Background:

• Organisms adapt to environmental changes using genetic diversity.
• The relative contribution of ancestral versus recently derived genetic variations to adaptation is often debated.
• Quantifying these contributions is crucial for understanding evolutionary dynamics.

Purpose of the Study:

• To experimentally quantify the relative contributions of ancestral and derived alleles to adaptation under cyclical selection.
• To investigate how mutation rates, population sizes, and fluctuation timescales influence adaptive strategies.
• To introduce a novel measure for quantifying the role of derived alleles in adaptation.

Main Methods:

• Utilized budding yeast strains with a URA3 gene tandem repeat under cyclical selection and counterselection.
• Characterized and quantified frameshift events in the URA3 gene over 12 selection cycles.
• Employed a general model of fluctuating selection to analyze dependencies on key parameters.

Main Results:

• Ancestral alleles accounted for 10-20% of all adaptive events observed.
• A sharp transition in adaptive dynamics was identified, shifting from selection on ancestral to derived alleles as fluctuation timescales increased.
• The de novo mutation rate along the ancestral lineage was used to quantify derived allele contributions.

Conclusions:

• Fluctuating selection can dynamically shift between reliance on ancestral and derived genetic variation for adaptation.
• This study provides a quantitative framework for understanding the interplay of different genetic resources in evolutionary adaptation.
• The findings have implications for predicting population responses to environmental change over evolutionary time.