Experimental evolution in silico: a custom-designed mathematical model for virulence evolution of Bacillus...

Area of Science:

• Evolutionary Biology
• Mathematical Modeling
• Microbiology

Background:

• Mathematical models of virulence evolution often assume mass action for parasite transmission, which is frequently violated in experimental settings.
• This discrepancy between theory and experiment necessitates new models tailored to controlled infection protocols.

Purpose of the Study:

• To develop and analyze a novel mathematical model that accurately reflects experimental evolution conditions.
• To explain empirical observations in the Bacillus thuringiensis-Caenorhabditis elegans model system regarding virulence evolution.

Main Methods:

• Proposed a mathematical model incorporating controlled parasite transmission (non-mass action), discrete host generations, and context-dependent toxin production costs.
• Analyzed the model to predict trends in virulence evolution under different experimental conditions.

Main Results:

• The model successfully replicated experimental findings, demonstrating that resistant hosts select for highly virulent bacterial strains.
• Evolved virulence levels were independent of initial virulence, and the quantity of ingested bacteria significantly influenced virulence evolution.
• Fewer ingested bacteria were shown to select for more virulent strains.

Conclusions:

• Custom-designed mathematical models are crucial for interpreting empirical results in experimental evolution studies.
• The study provides testable predictions for future experiments on virulence evolution and parasite adaptation.