1 research outputs found
Immune loss as a driver of coexistence during host-phage coevolution
Bacteria and their viral pathogens face constant pressure for augmented immune and infective
capabilities, respectively. Under this reciprocally imposed selective regime, we expect to see a
runaway evolutionary arms race, ultimately leading to the extinction of one species. Despite this
prediction, in many systems host and pathogen coexist with minimal coevolution even when wellmixed. Previous work explained this puzzling phenomenon by invoking fitness tradeoffs, which can
diminish an arms race dynamic. Here we propose that the regular loss of immunity by the bacterial
host can also produce host-phage coexistence. We pair a general model of immunity with an
experimental and theoretical case study of the CRISPR-Cas immune system to contrast the behavior
of tradeoff and loss mechanisms in well-mixed systems. We find that, while both mechanisms can
produce stable coexistence, only immune loss does so robustly within realistic parameter ranges