INTRODUCTION
Parasites are organisms that have adapted to live on or in a host organism in order to exploit the host’s resources (Combes 2001). Parasites (both macro- and micro-) can have considerable effects on host fitness and so act as a strong selective force for many organisms. This has favored traits allowing hosts to identify and avoid risks of parasitism in their environment. Parasite-avoidance mechanisms include identifying and avoiding vectors of parasites, infected conspecifics, contaminated areas, or aggregations of parasites (Curtis 2014). As such, parasite avoidance is anticipated to change how animals behave and utilize their environment. These avoidance behaviors are thought to impact various population, community, and ecosystem outcomes, recently referred to as the “landscape of disgust” hypothesis (Weinstein et al. 2018).
Here we examine the possibility that the avoidance of parasites by hosts could be influential in another manner: in fostering the evolution of dishonest signals and otherwise biasing signal evolution. Specifically, we outline situations where dishonest signals of infection could benefit infection-mimics, but also induce costs. We first make the case for the plausibility of the evolution of dishonest signals of infection. We then detail various situations where these signals could impact the fitness of their bearers and discuss systems that meet the preconditions necessary for them to evolve. We support aspects of this argument with a straightforward mathematical model that identifies the criteria under which “faking sick” can persist and which illustrates the dependence of this strategy on the prevalence of true parasites. By outlining scenarios in which the evolution of dishonest signals of infection are theoretically plausible, we hope to encourage consideration of less intuitive ways in which parasitism could impact animal communication systems, competition, social behavior, and sexual selection. For simplicity, we limit our discussion to intraspecific infection-mimicry as a male tactic, but our reasoning could apply to females in some cases.