No abstract

When predators consume prey, they risk becoming infected with their prey's parasites, which can then establish the predator as a secondary host. For example, stickleback in northern temperate lakes consume benthic or limnetic prey, which are intermediate hosts for distinct species of parasites (e.g. Eustrongylides nematodes in benthic oligocheates and Schistocephalus solidus copepods in limnetic copepods). These worms then establish the stickleback as a secondary host and can cause behavioral changes linked to increased predation by birds. In this study, we use a quantitative genetics framework to consider the simultaneous eco-evolutionary dynamics of predator ecomorphology and predator immunity when alternative prey may confer different parasite exposures. When evolutionary tradeoffs are sufficiently weak, predator ecomorphology * Corresponding author (samfleischer@ucdavis.edu) 1 and immunity are correclated among populations, potentially generating a negative correlation between parasite intake and infection.web dynamics and structure (Cortez and Weitz 2014;Lafferty et al. 2006;Velzen and Gaedke 2017). Recent food web models are thus incorporating the effects of diet-driven infection rates, which depend on a host's position within the food web. However, after a parasite passes through this 'encounter filter,' it must then pass through a 'compatibility filter' by establishing an infection despite the host's immune response. Therefore, to understand the role of parasitism within an ecological community we must consider both the host diet (encounters) and host immunity (compatibility).Recent empirical and theoretical studies on eco-evolutionary feedbacks can help us understand how predators can encounter different trophically-transmitted parasites. In particular, predator-prey interactions may drive trait evolution in the prey to facilitate predator evasion or in the predator to optimize foraging success. Yoshida et al. (2003) found that prey evolution can affect the period and phase difference in predator-prey cycles, and Becks et al. (2010) found that the amount of heritable variation in a prey defense trait can shift dynamics between equilibrium and oscillatory states. These example illustrate how trait evolution modifies predator-prey interactions in ways that can change their population dynamics, coexistence, food web structure, and, hence, the rate of predator enounter with

When predators consume prey, they risk becoming infected with their prey's parasites, which can then establish the predator as a secondary host. A predator population's diet therefore influences what parasites it is exposed to, as has been repeatedly shown in many species such as threespine stickleback (Gasterosteus aculeatus) (more benthic-feeding individuals obtain nematodes from oligocheate prey, whereas limnetic-feeding individuals catch cestodes from copepod prey). These differing parasite encounters, in turn, determine how natural selection acts on the predator's immune system. We might therefore expect that ecoevolutionary dynamics of a predator's diet (as determined by its ecomorphology) should drive correlated evolution of its immune traits. Conversely, the predator's immunity to certain parasites might alter the relative costs and benefits of different prey, driving evolution of its ecomorphology. To evaluate the potential for ecological morphology to drive evolution of immunity, and vice versa, we use a quantitative genetics framework coupled with an ecological model of a predator and two prey species (the diet options).Our analysis reveals fundamental asymmetries in the evolution of ecomorphology and immunity. When ecomorphology rapidly evolves, it determines how immunity evolves, but not vice versa. Weak trade-offs in ecological morphology select for diet generalists despite strong immunological trade-offs, but not vice versa. Only weak immunological trade-offs can explain negative diet-infection correlations across populations. The analysis also reveals that eco-evo-immuno feedbacks destabilize population dynamics when trade-offs are sufficiently weak and heritability is sufficiently high. Collectively, these results highlight the delicate interplay between multivariate trait evolution and the dynamics of ecological communities.