DISSERTATION RESEARCH: Evolutionary Consequences of Pathogen Strain Competition in an Emerging Fungal Disease

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This project will investigate the interplay of ecological competition and evolutionary dynamics among different strains of pathogenic fungi. Newly discovered, emerging diseases are a significant threat to biological diversity and human health. Many of these emerging diseases are caused by fungal pathogens. Yet few studies have addressed the evolutionary ecology of disease-causing fungi. A notorious emerging fungal disease is the amphibian-killing chytrid fungus, which is contributing to worldwide amphibian declines and biodiversity loss. Despite intensive research since its discovery in 1999, the origins and evolutionary trajectory of this disease remain a mystery. This project will investigate a region of high chytrid diversity in the Atlantic Forest of southern Brazil to understand how competition among different fungal strains determines the success and evolution of these pathogens. Understanding how emerging diseases evolve will be critical to controlling future disease outbreaks. The project includes the training of undergraduate and graduate students, along with K-12 outreach programs and museum displays that highlight effects of introduced diseases on ecosystem health.Prior research suggests that divergent amphibian-killing chytrid strains in Brazil's Atlantic Forest are competing for hosts. According to theory, competing disease strains should evolve to have faster rates of growth and increased virulence until a single most successful strain has eliminated all others. This project will investigate how these chytrid disease strains initially came into contact, and the ecological and evolutionary outcomes of this contact. The researchers will reconstruct the divergence history of Brazilian Atlantic Forest disease strains using whole genome sequences of pathogen isolates collected from the region. They will then conduct a cross-strain competition experiment on a model amphibian host. The genomes of experimental pathogen strains will be sequenced before and after the experiment to link genotypic changes to phenotypic change in post-competition virulence. These data will allow the researchers to establish the timing of contact between pathogen populations, and to determine if accelerated virulence evolves due to direct competition among strains.