American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Revisiting the role of hyperparasitism in evolution of virulence”

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Simran K. Sandhu, Andrew Yu. Morozov, Robert D. Holt, and Michael Barfield (Feb 2021)

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Hyperparasitism denotes the natural phenomenon where a parasite infecting a host is in turn infected by its own parasite. Hyperparasites can shape the dynamics of host-parasite interactions and often have a deleterious impact on pathogens, an important class of parasites, causing a reduction in their virulence and transmission rate. Hyperparasitism thus could be an important tool of biological control. However, host-parasite-hyperparasite systems have so far been outside the mainstream of modelling studies, especially those dealing with eco-evolutionary aspects of species interactions. Here we theoretically explore the evolution of life history traits in a generic host-parasite-hyperparasite system, focusing on parasite virulence and the positive impact hyperparasitism has on the host population. We also explore the co-evolution of life history traits of the parasite and hyperparasite, using adaptive dynamics and quantitative genetics frameworks to identify evolutionarily singular strategies. We find that in the presence of hyperparasites, the evolutionarily optimal pathogen virulence generally shifts towards more virulent strains. However, even in this case, the use of hyperparasites in biocontrol could be justified since overall host mortality decreases. An intriguing possible outcome of the evolution of the hyperparasite can be its evolutionary suicide.