Resumen
- The ongoing coevolutionary struggle between hosts and pathogens, with hosts evolving to escape pathogen infection and pathogens evolving to escape host defences, can generate an ‘arms race’, i.e., the occurrence of recurrent selective sweeps that each favours a novel resistance or virulence allele that goes to fixation. Host–pathogen coevolution can alternatively lead to a ‘trench warfare’, i.e., balancing selection, maintaining certain alleles at loci involved in host–pathogen recognition over long time scales