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Evolutionary instability of ectomycorrhizal symbioses in basidiomycetes

Nature volume 407, pages 506508 (28 September 2000) | Download Citation

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Abstract

Mycorrhizae, the symbiotic associations of plant roots and fungal hyphae, are classic examples of mutualisms. In these ecologically important associations, the fungi derive photosynthetic sugars from their plant hosts, which in turn benefit from fungus-mediated uptake of mineral nutrients. Early views on the evolution of symbioses suggested that all long-term, intimate associations tend to evolve toward mutualism. Following this principle, it has been suggested that mycorrhizal symbioses are the stable derivatives of ancestral antagonistic interactions involving plant parasitic fungi1. Alternatively, mutualisms have been interpreted as inherently unstable reciprocal parasitisms, which can be disrupted by conflicts of interest among the partners2,3,4,5. To determine the number of origins of mycorrhizae, and to assess their evolutionary stability, it is necessary to understand the phylogenetic relationships of the taxa involved. Here we present a broad phylogenetic analysis of mycorrhizal and free-living homobasidiomycetes (mushroom-forming fungi). Our results indicate that mycorrhizal symbionts with diverse plant hosts have evolved repeatedly from saprotrophic precursors, but also that there have been multiple reversals to a free-living condition. These findings suggest that mycorrhizae are unstable, evolutionarily dynamic associations.

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Acknowledgements

We thank M. Pagel for providing a copy of Discrete; USDA, DAOM and other sources for fungal samples; J.-M. Moncalvo and R. Vilgalys for access to unpublished sequences; and J. Bronstein for helpful comments. This work was supported by grants from the NSF.

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Author notes

    • David S. Hibbett
    • , Luz-Beatriz Gilbert
    •  & Michael J. Donoghue

    Present address: Department of Biology, Clark University, 950 Main Street, Worcester, Massachusetts 01610, USA (D.S.H.); Laboratory of Genetics, Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037-1099, USA (L.-B. G.); Department of Ecology and Evolutionary Biology, Yale University, P.O. Box 208106, New Haven, Connecticut 06520-8106, USA (M.J.D.).

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  1. *Harvard University Herbaria, 22 Divinity Avenue, Cambridge, Massachusetts 02138, USA

    • David S. Hibbett
    • , Luz-Beatriz Gilbert
    •  & Michael J. Donoghue

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Correspondence to David S. Hibbett.

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https://doi.org/10.1038/35035065

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