Genetic drift opposes mutualism during spatial population expansion.

Area of Science:

• Ecology
• Evolutionary Biology
• Microbiology

Background:

• Mutualistic interactions are crucial for species coexistence and genetic diversity.
• Spatial expansions can disrupt mutualisms due to genetic drift at the expansion front, leading to reduced diversity.
• Understanding the interplay between mutualism and spatial dynamics is key to predicting ecological outcomes.

Purpose of the Study:

• To investigate the antagonistic relationship between mutualism and genetic drift during spatial expansions.
• To determine how the strength and symmetry of mutualistic interactions influence diversity maintenance.
• To model the conditions under which mutualisms can persist during range expansions.

Main Methods:

• Utilized cross-feeding strains of Saccharomyces cerevisiae as a model system for mutualists.
• Grew yeast on agar surfaces to simulate spatial expansions.
• Manipulated nutrient exchange to vary the strength and symmetry of mutualistic interactions.

Main Results:

• Strong mutualism effectively suppressed genetic demixing during spatial expansions, preserving diversity.
• Weak or asymmetric mutualism was overwhelmed by genetic drift, resulting in slower growth and reduced diversity.
• Experimental data were used to parameterize theoretical models predicting demixed region size and mutualism survival.

Conclusions:

• The strength of mutualism is critical for maintaining diversity during spatial expansions.
• Genetic drift can disrupt beneficial mutualisms if they are not sufficiently strong or symmetric.
• Theoretical modeling provides a framework for understanding the ecological limits of mutualistic interactions in expanding populations.