LAUSR

Species from all five kingdoms of life have evolved sophisticated mechanisms to generate diversity in genes that are involved in host–pathogen interactions, conferring reduced levels of parasitism to both individuals and populations. Here, we highlight unifying concepts that underpin these evolutionarily unrelated diversity-generating mechanisms (DGMs). We discuss the mechanisms of and selective forces acting on these diversity-generating immune strategies, as well as their epidemiological and co-evolutionary consequences. We propose that DGMs can be broadly classified into two classes — targeted and untargeted DGMs — which generate different levels of diversity with important consequences for host–parasite co-evolution.