Biological Market example

underground nutrient trade

rhizobium-nodules on Acacia roots

(photo: Frank Brunner)

The cover of the 'microbial markets' paper by Werner et al (2014)


You can hear (and see) the quite amazing Toby Kiers talking about "mycorrhizal markets" and more here:

TED-talk (2019) "Lessons from fungi on markets and economics"

Mushroom revival podcast (2021) "The Mycorrizal Market Economy"

The mutualistic interactions between plants and mycorrhizal fungi and rhizobia (bacteria) provide ideal examples for tests of the biological market paradigm with traders belonging to two clear cut classes: plants and either fungi or bacteria.

The commodities exchanged on this sort of markets 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, nodules formed by root tissue and symbionts can be isolated and so forth.

Reviews contemplating the possibilities of applying biological market theory (BMT) to 'underground markets' can be found here:

... and a more critical review:

Toby Kiers and colleagues came to (verbal) blows with these authors:

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In 2018, I published a review together with Toby Kiers in which we tried to tackle the question of what exactly is a 'trader' on an underground market (Noë, R. & Kiers, E. T. (2018). Mycorrhizal markets, firms, and co-ops. Trends in Ecology & Evolution, 33(10), 777-789. pdf). This is a hairy question  (see also 'the agency problem' on the page 'microbial markets'), notably in the case of arbuscular mycorrhizal fungi (AMFs): which entity is the trading agent that decides about how much to trade and with whom and at what price? And, if plants indeed exert partner choice among their AMF-partners, what is the entity they choose: the whole fungal network (the mycelium, or fungal individual, if one can speak of individuals in this case)? Or, do they choose at the level of single arbuscules, the trading sites inside the root cells that are formed by both fungal and plant tissues?  The answer is probably a bit of both: small groups of fungal nuclei, which we called 'co-ops', perhaps determine what happens at the level of single arbuscules, but the whole mycelium also directs the nutrients it trades over long distances to patches where it fetches a better price, as is described in several other papers from the Kiers-lab. Here a few examples:

The economist Loch-Temzelides used the results of this study in his paper in PNAS (2021): "Walrasian equilibrium behavior in nature"  (see the page Biological Market models)

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In the fall of 2020 Prescott and colleagues published a paper in which they claimed that an organism does not (or cannot?) use a substance it produces as a commodity that can be traded against other commodities with mutualistic partners when this substance is a waste product - in this case surplus C produced by plants which is either stored in, or exudated by, their roots. I reacted to this paper with a short 'Letter' in the same journal, because I have the expression that this is a wide-spread fallacy in this particular sub-field of mutualism research.

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Brian Steidinger published an clever extension to BMT in which  he develops a model that would  explain how mycoheterotrophic plants (plants that are assumed to take up both carbon and other nutrients from fungi) could take part on markets by buying a nutrient from one partner and selling that same nutrient for a better price to another, which in economic jargon is called 'arbitrage'.  This also contradicts the paper by Walder and Van der Heijden (2015) mentioned above, by showing that 'arbitrage' is an alternative to the source-sink story, which is more a description than an explanation anyway.

A lot more information on mycorrhizal fungi, and the networks they form, can be found here: SPUN

Till about 2015 the literature in this field developed more or less independently from the literature on markets in vertebrates, but there were regular cross-references. The following papers describe market models based on these nutrient exchange mutualisms:

Sanctioning, a drastic form of partner choice

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. My first paper on the subject (Noë 1990) was cited by these authors, but I have little doubts that they would have had their brain wave without me too. A decade later the idea of sanctioning was further developed by Denison and colleagues.

Beautiful examples of these underground nutrient exchange markets, based on technically challenging experiments and inspired by biological market logic are given in: 

There are many more high-quality empirical papers on nutrient exchange markets, however, of which I list just a few that I found personally most appealing, especially because they give proper attention to partner choice.

 last update:  26 JUN 24