Host diversity limits the evolution of parasite local adaptation

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Host-parasite specificity can drive local adaptation.
• Host genetic diversity is predicted to limit parasite local adaptation by reducing infectivity.
• CRISPR-Cas systems in bacteria provide adaptive immunity against phages.

Purpose of the Study:

• To empirically test if host genetic diversity, specifically CRISPR allele diversity, affects parasite (bacteriophage) local adaptation.
• To investigate the relationship between the diversity of clustered regularly interspaced short palindromic repeats (CRISPR) alleles in bacterial hosts and the adaptive potential of their phages.

Main Methods:

• Utilized the specific interaction between bacteria with CRISPR-Cas immunity and their bacteriophages.
• Manipulated the diversity of CRISPR alleles within experimental bacterial populations.
• Assessed phage infectivity and adaptation to bacterial hosts under varying levels of CRISPR diversity.

Main Results:

• High CRISPR allele diversity in bacterial populations prevented local adaptation of bacteriophages.
• Bacteriophages could achieve local adaptation to bacterial hosts, but only when CRISPR allele diversity was experimentally reduced.
• Naturally evolved high CRISPR diversity effectively limits phage adaptation.

Conclusions:

• Bacterial CRISPR allele diversity plays a crucial role in preventing parasite local adaptation.
• The level of host genetic diversity directly influences the capacity for host-parasite coevolution and local adaptation.
• CRISPR-Cas systems are a key factor in mediating the impact of host diversity on parasite evolution.