Population size impacts host-pathogen coevolution.

Area of Science:

• Evolutionary biology
• Microbial ecology
• Population genetics

Background:

• Host-pathogen interactions drive rapid coevolutionary adaptation.
• Finite population sizes theoretically limit genetic diversity and selection efficiency due to genetic drift.
• Experimental evidence for population size constraints on coevolution is limited.

Purpose of the Study:

• To experimentally assess the influence of host population size on coevolutionary dynamics.
• To investigate how genetic drift and selection efficiency are affected by population size in host-pathogen systems.
• To determine the impact of population bottlenecks on coevolutionary trajectories.

Main Methods:

• Utilized Caenorhabditis elegans (host) and Bacillus thuringiensis (pathogen) for experimental coevolution.
• Manipulated host population sizes into small, large, and periodically bottlenecked groups over 23 generations.
• Controlled host population size meticulously throughout the experimental duration.

Main Results:

• Host adaptation was significantly constrained in small host populations.
• Bottlenecked populations exhibited constraints on adaptation to a lesser extent than small populations.
• Coevolution in large versus small populations resulted in distinct selection dynamics and genotype-by-genotype interaction patterns.

Conclusions:

• Host population size is a critical factor influencing the pace and pattern of antagonistic coevolution.
• Limited population size and bottlenecks can impede the co-adaptive potential between hosts and pathogens.
• The findings highlight the importance of population dynamics in shaping evolutionary trajectories of interacting species.