Predation shifts coevolution toward higher host contact rate and parasite virulence

Abstract

Hosts can avoid parasites (and pathogens) by reducing social contact, but such isolation may carry costs, e.g. increased vulnerability to predators. Thus, many predator–host–parasite systems confront hosts with a trade-off between predation and parasitism. Parasites, meanwhile, evolve higher virulence in response to increased host sociality and consequently, increased multiple infections. How does predation shift coevolution of host behaviour and parasite virulence? What if predators are selective, i.e. predators disproportionately capture the sickest hosts? We answer these questions with an eco-coevolutionary model parametrized for a Trinidadian guppy– Gyrodactylus spp. system. Here, increased predation drives host coevolution of higher grouping, which selects for higher virulence. Additionally, higher predator selectivity drives the contact rate higher and virulence lower. Finally, we show how predation and selectivity can have very different impacts on host density and prevalence depending on whether hosts or parasites evolve, or both. For example, higher predator selectivity led to lower prevalence with no evolution or only parasite evolution but higher prevalence with host evolution or coevolution. These findings inform our understanding of diverse systems in which host behavioural responses to predation may lead to increased prevalence and virulence of parasites.

Sex-specific immunocompetence: resistance and tolerance can both be futile but not under the same circumstances

“…Futility is typically discussed with respect to resistance: if parasite encounter rates are so high that strongly resistant hosts still become infected, then, assuming a trade-off between resistance and current reproduction, reduced investment into resistance is selected for (Jokela et al 2000;Walsman et al, 2023). This may involve 'classical' resistance, as well as any behavioural avoidance of parasites (Walsman et al, 2022(Walsman et al, , 2023. The "futility" cases are a counterexample to the intuition that more abundant parasites lead to stronger host immune defences (Lindström et al, 2004).…”

“…2000; Walsman et al ., 2023). This may involve ‘classical’ resistance, as well as any behavioural avoidance of parasites (Walsman et al ., 2022, 2023). The “futility” cases are a counterexample to the intuition that more abundant parasites lead to stronger host immune defences (Lindström et al ., 2004).…”

Despite COVID: showcasing new research in evolutionary biology from academic care-givers in the middle of a pandemic

“…B 289: 20222131 low-predation environments to demonstrate evidence for rapid parallel evolution in microbiome composition in response to the change in environmental conditions. Walsman et al [23] use an eco-evolutionary model, inspired by a guppy system, to explore how behavioural responses of prey to predation risk may lead to increased prevalence and virulence of parasites owing to changes in grouping behaviour. Kanwal & Gardner [24] modelled the role of population viscosity on kin selection, finding that if dispersal is conditional upon local density, individuals in more altruistic neighbourhoods disperse more frequently and kin competition is relaxed, leading to a negative correlation between dispersal and altruism.…”