PT  - JOURNAL ARTICLE
AU  - Jake L Weissman
AU  - Rayshawn Holmes
AU  - Rodolphe Barrangou
AU  - Sylvain Moineau
AU  - William F Fagan
AU  - Bruce Levin
AU  - Philip L F Johnson
TI  - Immune Loss as a Driver of Coexistence During Host-Phage Coevolution
AID  - 10.1101/105908
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 105908
4099  - http://biorxiv.org/content/early/2017/07/10/105908.short
4100  - http://biorxiv.org/content/early/2017/07/10/105908.full
AB  - 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 well-mixed. 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.