Our research centers on the ecology, evolution, and systematics of symbiotic fungi. As a group, we are inspired by the astonishing diversity of the organisms we study. Here’s a tour of a few of our recently supported research topics.
Diversity and demographic effects of seed-infecting fungi in tropical forests
| Fungal pathogens are increasingly recognized as an important source of adult-plant and seedling mortality in tropical forests, influencing tree demography, distributions, and diversity. However, very little is known regarding the cryptic effects of tropical seed-infecting fungi, including endophytes, pathogens, and saprotrophs that decay seed tissues in soil. Seed-infecting fungi are likely to be especially important for tree species depending upon seed survival in soil (seed banks) for successful recruitment, including pioneer species - the trees that rapidly exploit treefall gaps and comprise the first steps in tropical forest succession. We are working in collaboration with Dr. Jim Dalling (University of Illinois) and Rachel Gallery (Ph.D. student in the Dalling lab) to characterize seed-infecting fungi associated with focal seed-bank-dependent tropical trees (Cecropia spp.) in three tropical forests (Costa Rica, Panama, Ecuador). Our work synthesizes field studies of seed demography with molecular analysis of fungal communities, providing a first glimpse at the diversity, spatial structure, and ecological roles of these little-known fungal assemblages.
Funding: NSF Collaborative Research Grant to Dalling and Arnold (2004-2007); NSF REU Supplement to Arnold (2006)
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Bacterial endosymbionts of fungal endophytes
| Fungal endophytes live within healthy plant tissues without causing disease. These fungi represent apparently avirulent symbionts that are closely related to pathogenic species, and recent analyses have shown that endophytism and pathogenicity are intimately linked over the evolution of the Ascomycota. These observations raise the question: what factors influence the virulence of fungi associated with living plant tissues? Several other labs have shown that endosymbiotic bacteria inhabiting fungi can influence the virulence of their hosts. Work by Michele Hoffman in our lab has shown that apparently pure genomic DNA from fungal endophyte cultures often contains bacterial DNA. We are testing the hypothesis that bacterial endosymbionts influence the fungal phenotype and ultimately, the outcome of plant-fungus interactions.
Funding: NSF Microbial Biology Starter Grant to Arnold (PI) (2006-2007)
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Beta diversity of tropical fungal endophytes
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Fungal endophytes are highly abundant and diverse in leaves of tropical trees, but the scale of their diversity is unclear: disparate studies are generally not comparable due to differences in endophyte isolation methods and fungal species concepts. Accordingly, beta diversity of tropical endophytes remains unknown, and the degree to which different ecological or geographic factors shape endophyte communities has not been examined. With the development of the network of Forest Dynamics plots through the Center for Tropical Forest Science, we have a critical tool for coherent studies of alpha diversity at multiple sites; for explicit examination of beta diversity among sites; and for hypothesis testing with regard to the importance of forest diversity, host plant frequency, and abiotic factors such as precipitation in shaping host-endophyte associations. We are conducting a three-year study to assess the endophytic flora of three tropical forests (Mudumalai Forest Reserve, India; Korup, Cameroon; Barro Colorado Island, Panama). Our study asks: what factors shape fungal symbiont communities in tropical forests?
Funding: Center for Tropical Forest Science grant to Arnold (PI) and T.S. Suryanarayanan (2006-2008) and Indo-US Technology Forum (2006)
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Cryptic biodiversity of Diné Bikéyah: Fungal endophytes of the Navajo Nation
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Fungal endophytes are ubiquitous among terrestrial plants, can confer significant ecological benefits on their hosts, are closely related to pathogens, and move across borders during plant introductions. However, little is known regarding their diversity and species composition in most host plants, and their cryptic roles in facilitating invasion by the plants that harbor them have not been explored. We are conducting an 18-month study to examine the ecological roles of fungal endophytes in the context of one of the most dramatic landscapes in the arid west: the Colorado Plateau, with a special focus on Diné Bikéyah (the Navajo Nation). The goals of this project are (1) to provide a first understanding of the morphological and molecular diversity of fungal communities associated with native and non-native plants of Diné Bikéyah; (2) to examine diverse symbiont communities for taxa with potential use in biological control of tamarisk (salt-cedar), one of the most devastating invaders in western waterways; and (3) to provide a unique, on-Nation research experience for Navajo undergraduates through Diné College, Tsaile, Arizona.
Funding: USDA Tribal College Grant to Barb Klein (PI), Mary Shimabukuro, and Arnold (2006-2007)
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