Document: ANN-3-54-2

Winners never cheat; cheaters never win: Species' flexibility and the symmetry of benefit within a mutualism of arbuscular mycorrhizal fungi and plants.

PRINGLE, A.* ¹, J.D.BEVER ² and J.ANTONOVICS ³

Duke University, Durham NC 27708, USA ¹
University of California, Irvine CA, USA ²
University of Virginia, Charlottesville VA, USA ³

Abstract:
Mutualisms are constantly exposed to non-mutualistic "cheaters", or parasites. In tightly coevolved mutualisms, for example the mutualism between figs and fig wasps, species of fig wasp are either parasites or mutualists. In diffuse mutualisms, in which multiple partners interact, species may be more flexible and act as mutualists of one associate but parasites of another. Arbuscular mycorrhizal fungi (AMF) inhabit the roots of plants and provide phosphorus to plants in exchange for photosynthetically derived carbon. The relationship is a classic, and diffuse, mutualism. We have used a variety of species isolated from an old field community to explore interactions between pairs of plants and AMF. We ask 1) are species of plant and fungus strict mutualists or parasites? and 2) are there constraints to parasitism? We have found that species are not strictly mutualists or parasites, rather, predicting the net costs and benefits of a particular association requires a knowledge of the specific combination of plant and fungus. For example, plant shoots of Anthoxanthum odoratum are significantly heavier in association with the fungus Gigaspora gigantea versus the fungus Glomus "white", however, shoots of Rumex acetosella are significantly heavier with G. "white" versus G. gigantea. G. gigantea is a relative mutualist in combination with A. odoratum, but a relative parasite in combination with R. acetosella. Interactions may be weakly asymmetric. For example, the fungus Acaulospora trappei derives its greatest benefit from association with the plants Veronica arvensis and Plantago lanceolata, however, the fungus gives its greatest benefit to the plant Allium vineale. Despite this example, investments by plants and AMF are typically reciprocal: if a plant grows larger with a specific fungus, the fungus is likely to sporulate disproportionately in association with the same plant. This kind of reciprocity may constrain the evolution of parasitism within the mutualism.

Keywords: mutualism, AMF, AM Fungi, cheating, parasitism

This abstract is being presented at: 9:15 AM in session:
Oral Session #8: Mycorrhizal Fungi.