Bridget Barker PhD Candidate Genetics GIDP Gordon Research Conference on Cellular and Molecular Fungal Biology Holderness, NH June 29-July 4, 2008 “Evidence for Hybridization and Introgression among Coccidioides species”

Coccidioides is a soil-dwelling dimorphic fungus endemic to the southwestern United States, Northern Mexico, and semi-arid portions of Central and South America. The saprobic mycelia produce asexual arthrospores, which when inhaled, can develop into pathogenic spherules. If the immune system cannot control the infection, the result is coccidioidomycosis, or San Joaquin Valley fever, a lung disease of humans and other mammals. In some cases, the fungus can disseminate beyond the lungs and cause fungal meningitis, which can be fatal if not treated. As of January 2008, fourteen strains of the fungus have been sequenced. These sequenced strains represent variation in biogeography, phenotype, and isolate source. In 2002, the genus Coccidioides was divided into two closely related species. Additionally, at the population level, both species are divided into at least two populations: northern and southern California for C. immitis, and Arizona/Mexico and Texas/South America for C. posadasii. The sharpness of the geographical separation of the populations is ambiguous, as some isolates obtained from patients in California were identified as C. posadasii and some patients from Texas, Arizona and Mexico were infected with C. immitis. Atypical infections may be due to patients traveling to and being exposed in other regions than where they were diagnosed, or due to long distance wind dispersal of infective arthrospores that occur in soil. The nature of the species boundary is of particular interest because of our recently discovered evidence of hybridization and introgression of blocks of C. posadasii DNA into C. immitis. This discovery was contingent on 1) previous studies that recognized phylogenetic species, and 2) ongoing analyses of data from the Coccidioides genome project, which will feature the largest number of genomes sequenced of any eukaryotic system, allowing for comparative genomic studies at the species and population levels.