Genetic drift and selection in many-allele range expansions

Area of Science:

• Evolutionary Biology
• Microbial Ecology
• Mathematical Modeling

Background:

• Range expansions are crucial in microbial ecology.
• Understanding competing strain dynamics is key to predicting evolution.
• Radially expanding colonies offer a model system for studying these dynamics.

Purpose of the Study:

• To investigate the evolutionary dynamics of competing E. coli strains.
• To compare experimental data with numerical simulations.
• To develop a predictive model for microbial range expansions.

Main Methods:

• Experimental observation of four competing E. coli strains in radially expanding colonies.
• Numerical simulations using a 1D ring model of biased random walkers.
• Analysis of average strain fractions, correlation functions, and domain wall dynamics.
• Development of a new technique to measure small selective differences.

Main Results:

• Evolutionary dynamics collapse onto master curves governed by three key parameters.
• Selection dominates over genetic drift beyond a specific expansion length.
• A dimensionless constant quantifies the interplay of colony curvature and selection.
• Simulations accurately predict experimental dynamics without additional fitting.

Conclusions:

• The random walk model is a powerful predictive tool for microbial range expansions.
• The model accurately describes the evolutionary dynamics of multiple genotypes with varying fitnesses.
• Key parameters identified provide insights into the balance of selection and drift.