The mutualistic interactions between plants and mycorrhizal fungi and rhizobia (bacteria) provide ideal examples for tests of the biological market paradigm. The 'traders' are divided in two clear-cut classes of which one consists of very few large individuals (the plants) and the other of huge numbers of very small individuals (the fungi and bacteria).
The commodities exchanged on this sort of market are nutrients, which makes it possible to quantify exchanges, at least for those who know how to do this. These systems are also ideally suited for experiments: nutrients can be added, the same individual can interact with different partners in split-root experiments and so forth.
The literature in this field developed more or less in parallel to the literature on markets in vertebrates, but there are regular cross-references. Some important theoretical papers have been based on these systems, which made use of existing models and techniques in economics: Schwartz & Hoeksema (1998); Hoeksema & Schwartz (2003) and Kummel & Salant (2006).
Sanctioning
A phenomenon often described here is 'sanctioning', i.e. breaking off the relationship with a partner. An example would be a plant cutting off supplies to a nodule with rhizobia that are less productive than others. 'Sanctioning' is a form of partner choice with usually more drastic results than 'punishment', which is more likely to occur on markets with less extreme power differentials between partners.
The idea of sanctioning as a selective force goes back to a seminal paper by Bull & Rice (1991) on selective abortion of figs (see my page on Obligate pollination mutualisms). My first paper on the subject (Noë 1990) was cited by the authors, but I have little doubts that they would have had their brain wave without me too.
There are many high-quality empirical papers in this field of which I list just a few: West et al. 2002; Simms et al. 2006: Kiers & van der Heijden 2006 (see also reviews by Simms & Taylor 2002; Bshary & Bronstein 2004).
References
Bshary, R. & Bronstein, J. L. 2004. Game structures in mutualistic interactions: What can the evidence tell us about the kind of models we need? In: Advances in the Study of Behavior, Vol 34, pp. 59-101. San Diego: Elsevier Academic Press Inc.
Bull, J. J. & Rice, W. R. 1991. Distinguishing mechanisms for the evolution of co-operation. Journal of Theoretical Biology, 149, 63-74.
Hoeksema, J. D. & Schwartz, M. W. 2003. Expanding comparative-advantage biological market models: contingency of mutualism on partners’ resource requirements and acquisition trade-offs. Proceedings of the Royal Society B-Biological Sciences, 270, 913-919.
Kiers, E. T. & van der Heijden, M. G. A. 2006. Mutualistic stability in the arbuscular mycorrhizal symbiosis: Exploring hypotheses of evolutionary cooperation. Ecology, 87, 1627-1636
Kummel, M. & Salant, S. W. 2006. The economics of mutualisms: optimal utilization of mycorrhizal mutualistic partners by plants. Ecology, 87, 892-902.
Noë, R. 1990. A Veto game played by baboons: a challenge to the use of the Prisoner's Dilemma as a paradigm for reciprocity and cooperation. Animal Behaviour, 39, 78-90.
Schwartz, M. W. & Hoeksema, J. D. 1998. Specialization and resource trade: biological markets as a model of mutualisms. Ecology, 79, 1029-1038.
Simms, E. L. & Taylor, D. L. 2002. Partner choice in nitrogen-fixation mutualisms of legumes and rhizobia. Integrative and Comparative Biology 42:369-380.
Simms, E. L., Taylor, D. L., Povich, J., Shefferson, R. P., Sachs, J. L., Urbina, M. & Tausczik, Y. 2006. An empirical test of partner choice mechanisms in a wild legume-rhizobium interaction. Proceedings of the Royal Society B-Biological Sciences, 273, 77-81.
West, S. A., Kiers, E. T., Simms, E. L. & Denison, R. F. 2002. Sanctions and mutualism stability: why do rhizobia fix nitrogen? Proceedings of the Royal Society of London Series B-Biological Sciences, 269, 685-694.
