Kasson, M.T., Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park, PA 16802, United States
O'Donnell, K., Bacterial Foodborne Pathogens and Mycology Research Unit, National Center for Agricultural Utilization Research, US Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL 61604, United States
Rooney, A.P., Crop Bioprotection Research Unit, National Center for Agricultural Utilization Research, US Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL 61604, United States
Sink, S., Bacterial Foodborne Pathogens and Mycology Research Unit, National Center for Agricultural Utilization Research, US Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL 61604, United States
Ploetz, R.C., University of Florida, IFAS Tropical Research and Education Center, Homestead, FL 33031, United States
Ploetz, J.N., University of Florida, IFAS Tropical Research and Education Center, Homestead, FL 33031, United States
Konkol, J.L., University of Florida, IFAS Tropical Research and Education Center, Homestead, FL 33031, United States
Carrillo, D., University of Florida, IFAS Tropical Research and Education Center, Homestead, FL 33031, United States
Freeman, S., Institute of Plant Protection, ARO, The Volcani Center, Bet Dagan 50250, Israel
Mendel, Z., Institute of Plant Protection, ARO, The Volcani Center, Bet Dagan 50250, Israel
Smith, J.A., School of Forest Resources and Conservation, University of Florida, Gainesville, FL 32611, United States
Black, A.W., School of Forest Resources and Conservation, University of Florida, Gainesville, FL 32611, United States
Hulcr, J., School of Forest Resources and Conservation, University of Florida, Gainesville, FL 32611, United States
Bateman, C., School of Forest Resources and Conservation, University of Florida, Gainesville, FL 32611, United States
Stefkova, K., University of South Bohemia, 370 05 Ceske Budejovice, Czech Republic
Campbell, P.R., Queensland Department of Agriculture, Fisheries and Forestry and The Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Ecosciences Precinct, Dutton Park, Qld 4102, Australia
Geering, A.D.W., Queensland Department of Agriculture, Fisheries and Forestry and The Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Ecosciences Precinct, Dutton Park, Qld 4102, Australia
Dann, E.K., Queensland Department of Agriculture, Fisheries and Forestry and The Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Ecosciences Precinct, Dutton Park, Qld 4102, Australia
Eskalen, A., Department of Plant Pathology and Microbiology, University of California, Riverside, CA 92521, United States
Mohotti, K., Entomology and Nematology Division, Tea Research Institute of Sri Lanka, Talawakele 22100, Sri Lanka
Short, D.P.G., Department of Plant Pathology, University of California, Davis, 1636 E Alisal Street, Salinas, CA 93905, United States
Aoki, T., National Institute of Agrobiological Sciences, Genetic Resources Center, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan
Fenstermacher, K.A., Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park, PA 16802, United States
Davis, D.D., Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park, PA 16802, United States
Geiser, D.M., Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park, PA 16802, United States

Ambrosia beetle fungiculture represents one of the most ecologically and evolutionarily successful symbioses, as evidenced by the 11 independent origins and 3500 species of ambrosia beetles. Here we document the evolution of a clade within Fusarium associated with ambrosia beetles in the genus Euwallacea (Coleoptera: Scolytinae). Ambrosia Fusarium Clade (AFC) symbionts are unusual in that some are plant pathogens that cause significant damage in naïve natural and cultivated ecosystems, and currently threaten avocado production in the United States, Israel and Australia. Most AFC fusaria produce unusual clavate macroconidia that serve as a putative food source for their insect mutualists. AFC symbionts were abundant in the heads of four Euwallacea spp., which suggests that they are transported within and from the natal gallery in mandibular mycangia. In a four-locus phylogenetic analysis, the AFC was resolved in a strongly supported monophyletic group within the previously described Clade 3 of the Fusarium solani species complex (FSSC). Divergence-time estimates place the origin of the AFC in the early Miocene ~21.2. Mya, which coincides with the hypothesized adaptive radiation of the Xyleborini. Two strongly supported clades within the AFC (Clades A and B) were identified that include nine species lineages associated with ambrosia beetles, eight with Euwallacea spp. and one reportedly with Xyleborus ferrugineus, and two lineages with no known beetle association. More derived lineages within the AFC showed fixation of the clavate (club-shaped) macroconidial trait, while basal lineages showed a mix of clavate and more typical fusiform macroconidia. AFC lineages consisted mostly of genetically identical individuals associated with specific insect hosts in defined geographic locations, with at least three interspecific hybridization events inferred based on discordant placement in individual gene genealogies and detection of recombinant loci. Overall, these data are consistent with a strong evolutionary trend toward obligate symbiosis coupled with secondary contact and interspecific hybridization. © 2013 Elsevier Inc.