To be resistant or tolerant: the evolution of mixed defence strategies

Abstract

Theory predicts that resistance and tolerance represent mutually exclusive strategies of host defence. However, empirical evidence reveals that individual hosts simultaneously allocate resources to both mechanisms. Understanding the maintenance of this defence pattern remains controversial because empirical evidence is at odds with theoretical assumptions. Here, we present a novel host-enemy dynamic that considers: the differential effect of each defence strategy upon the evolutionary response of natural enemies; the process of local adaptation of the natural enemies to their hosts and the effect of negative and positive frequency-dependent selection acting on resistance and tolerance respectively. Our analysis suggests that a mixed pattern of defence allocation could be evolutionary stable because of the differential dynamic that each strategy has in the interaction with natural enemies.