OSIB: DYNAMIC INTERACTIONS BETWEEN HOST SOCIAL BEHAVIOR AND PARASITE VIRULENCE

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

Infectious diseases pose a fundamental threat to humans and the plants and animals we depend on. As demonstrated by the COVID-19 pandemic, how an infectious disease outbreak progresses depends critically on host behavior: the more social interaction between hosts, the faster the parasites that cause such diseases spread. We often assume that this faster spread leads to large, well-mixed parasite populations with high potential for rapid evolutionary increase in ‘virulence’, the rate at which they kill hosts. However, robust evidence supporting these assumptions is rare, and there are several complicating factors. First, animals often ‘socially distance’ in response to an outbreak, reducing transmission, and presumably affecting parasite populations and their evolution. Second, the magnitude of social distancing likely depends on parasite virulence. Third, across birds, mammals, and fish, more social host individuals are often better able to limit parasite growth, and may be less likely to transmit their infection. To unravel the complex interactions between host social behavior, parasite transmission, and virulence evolution, the research team will integrate mathematical models, experimental epidemics, and surveys of natural epidemics. They will use the Trinidadian guppy and a parasitic worm that grows on its skin in the first tests of many fundamental assumptions in evolutionary epidemiology. During their research, the team will train Trinidadian wildlife managers and students, develop curricula for Pennsylvanian schools, and train a diverse group of US-based scientists. The project will dramatically improve our general ability to predict how behavior affects disease spread and evolution across human and animal populations. Host behavior is the single biggest gap in our understanding of infectious disease dynamics. This project will provide unique insight into the fundamental interactions between behavioral, disease and evolutionary ecology that together dictate the trajectory of epidemics and parasite virulence evolution. Importantly, the research team will conduct the first experimental test of how host social behavior drives parasite virulence evolution. They combine this large-scale experimental approach with theory to evaluate the relative importance of the multiple dynamic, eco-evolutionary pathways by which host social behavior, parasite transmission, and virulence evolution interact: each pathway has received theoretical support but lacks robust empirical test in any system. Finally, they will validate the general framework built from their experiment and theory with observational data from natural communities. They will use this integrative approach to test how host social behavior: 1) shapes the size and structure of parasite populations; 2) drives parasite virulence evolution through selective and non-selective mechanisms; 3) responds to an outbreak to slow its spread. The Trinidadian guppy-Gyrodactylus system the team uses allows them to examine how a ubiquitous ecological context, predation, may affect virulence evolution: virulence evolution research mostly ignores ecology, but zoonotic spillover of wildlife pathogens from such contexts is a key route of disease emergence in humans. The framework produced will apply to all systems in which hosts are social, pathogens are contagious, coinfections are possible, and transmission and virulence trade off. These conditions have all been demonstrated in human pathogens and are likely met across systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.