Greater Phage Genotypic Diversity Constrains Arms-Race Coevolution

Area of Science:

• Evolutionary biology
• Ecology
• Microbial genetics

Background:

• Antagonistic coevolution between hosts and parasites is crucial in ecology and evolution.
• The balance of genetic variation in host resistance and parasite infectivity influences coevolutionary dynamics.
• Previous studies manipulated genetic diversity, but the impact of initial diversity on host-parasite coevolution remains unclear.

Purpose of the Study:

• To investigate how initial parasite genotypic diversity affects host-parasite coevolutionary dynamics.
• To determine if increased parasite diversity provides an evolutionary advantage.
• To explore implications for phage therapy and host-parasite interactions.

Main Methods:

• Co-evolution experiments involving the bacterium *Pseudomonas fluorescens* SBW25 and its lytic bacteriophage SBW25ɸ2.
• Experimental groups included bacteria evolved with one phage genotype (isolation) and bacteria evolved with two phage genotypes (together).
• Monitored reciprocal evolution of bacterial resistance and phage infectivity over time.

Main Results:

• Bacterial populations rapidly evolved resistance, and phages evolved increased infectivity in response.
• In isolation, both host resistance and parasite infectivity increased, indicating an evolutionary arms race.
• When evolved with two phage genotypes, bacteria failed to increase resistance, suggesting an inability to overcome multiple phage types simultaneously.
• Increased initial parasite genotypic diversity arrested long-term coevolution.

Conclusions:

• Initial parasite genotypic diversity can confer an evolutionary advantage, potentially halting coevolution.
• This finding has significant implications for the application of phage therapy.
• Understanding the role of parasite diversity is essential for broader ecological and evolutionary theory.