Evolution of Parasite Specialization Across an Ancient Agricultural System

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All parasites are specialists. This specialization is driven by the need for parasites to efficiently encounter and infect at least some hosts, which often comes at the cost of being able to infect others. At a broad-scale, parasite species adapt to a particular set of host species. At a finer-scale, many parasite strains specialize at overcoming the defenses of a narrow range of host genotypes within a species. There is little understanding of how evolutionary processes of host and parasite adaptation at the fine scale are linked to the evolution of parasite host ranges at broader scales, in part because few host-parasite systems are amenable to research at both scales. In this project the researchers will capitalize on a natural, ancient host-parasite system that allows for molecular investigation of parasite specialization at multiple scales. Escovopsis is a diverse genus of parasitic fungus that attacks other fungi cultivated by fungus-growing ants. Different Escovopsis species are able to infect different species of cultivated fungi, and at a finer scale, different Escovopsis genotypes are able to infect and utilize different host genotypes. Such parasite specificity suggests a dynamic pattern of adaptation and provides a rare opportunity to identify traits underlying parasite specialization at multiple scales. As part of this project, classes of undergraduate students will study parasite evolution through investigation of the parasites' host ranges and the parasites' genomes, and middle school students will learn about parasite evolution through an integrated science and art approach. Building on existing knowledge of Escovopsis diversity and host range, as well as recently gained insights into the Escovopsis genome, the researchers will couple experimental assays of parasite-host interactions, transcriptomics, population genomics and genetic manipulation to explore the genetic underpinnings of pathogen specialization. Specifically, the researchers will utilize transcriptomics and functional assays to identify the gene underlying the parasites' responses to host strains that they can and cannot infect. They will study the evolution of these genes in light of the evolution of the rest of the parasite genome through genomic comparisons across species and across strains within species. Taken together, the researchers will be able to assess whether similar traits underlie parasite specialization at broad and fine evolutionary scales in a tractable, ancient host-parasite system.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.