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The role of epiphytism in architecture and evolutionary constraint within mycorrhizal networks of tropical orchids

Authors

  • FLORENT MARTOS,

    1. Université de La Réunion, Peuplements Végétaux et Bioagresseurs en Milieu Tropical (UMR C53), Equipe Dynamiques écologiques au sein des écosystèmes naturels, 15 Avenue René Cassin, BP 7151, 97715 Saint-Denis Cedex 9, France
    2. Centre d’Ecologie Fonctionnelle et Evolutive (CNRS, UMR 5175), Département Interactions, Biologie et Sociétés, 1919 Route de Mende, 34293 Montpellier Cedex 5, France
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    • Present address: School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa.

  • FRANÇOIS MUNOZ,

    1. Université Montpellier 2, botAnique et bioinforMatique de l’Architecture des Plantes (UMR AMAP), Equipe Organisation et dynamique des peuplements et des paysages, Boulevard de la Lironde, TA A-51/PS2, 34398 Montpellier Cedex 5, France
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  • THIERRY PAILLER,

    1. Université de La Réunion, Peuplements Végétaux et Bioagresseurs en Milieu Tropical (UMR C53), Equipe Dynamiques écologiques au sein des écosystèmes naturels, 15 Avenue René Cassin, BP 7151, 97715 Saint-Denis Cedex 9, France
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  • INGRID KOTTKE,

    1. Eberhard-Karls-University Tübingen, Evolutionary Ecology of Plants, Auf der Morgenstelle 1, 72076 Tübingen, Germany
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  • CÉDRIC GONNEAU,

    1. Université de La Réunion, Peuplements Végétaux et Bioagresseurs en Milieu Tropical (UMR C53), Equipe Dynamiques écologiques au sein des écosystèmes naturels, 15 Avenue René Cassin, BP 7151, 97715 Saint-Denis Cedex 9, France
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  • MARC-ANDRÉ SELOSSE

    1. Centre d’Ecologie Fonctionnelle et Evolutive (CNRS, UMR 5175), Département Interactions, Biologie et Sociétés, 1919 Route de Mende, 34293 Montpellier Cedex 5, France
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Dr. Florent Martos, Fax: +27 33 2605105; E-mail: florentmartos@gmail.com

Abstract

Characterizing the architecture of bipartite networks is increasingly used as a framework to study biotic interactions within their ecological context and to assess the extent to which evolutionary constraint shape them. Orchid mycorrhizal symbioses are particularly interesting as they are viewed as more beneficial for plants than for fungi, a situation expected to result in an asymmetry of biological constraint. This study addressed the architecture and phylogenetic constraint in these associations in tropical context. We identified a bipartite network including 73 orchid species and 95 taxonomic units of mycorrhizal fungi across the natural habitats of Reunion Island. Unlike some recent evidence for nestedness in mycorrhizal symbioses, we found a highly modular architecture that largely reflected an ecological barrier between epiphytic and terrestrial subnetworks. By testing for phylogenetic signal, the overall signal was stronger for both partners in the epiphytic subnetwork. Moreover, in the subnetwork of epiphytic angraecoid orchids, the signal in orchid phylogeny was stronger than the signal in fungal phylogeny. Epiphytic associations are therefore more conservative and may co-evolve more than terrestrial ones. We suggest that such tighter phylogenetic specialization may have been driven by stressful life conditions in the epiphytic niches. In addition to paralleling recent insights into mycorrhizal networks, this study furthermore provides support for epiphytism as a major factor affecting ecological assemblage and evolutionary constraint in tropical mycorrhizal symbioses.

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