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Economic contract theory tests models of mutualism
E Glen Weyl1, Megan E Frederickson, Douglas W Yu
1Harvard University, Cambridge, MA 02138, USA.
Summary
Mutualisms persist not because of costly punishment (host sanctions), but through partner fidelity feedback. This mechanism, where host and symbiont fitness are linked, stabilizes even horizontally transmitted relationships, explaining why punishment isn't universal.
Area of Science:
- Evolutionary biology
- Ecology
- Game theory
Background:
- Mutualisms are crucial for ecological communities and life's diversification.
- Understanding cooperation often focuses on within-species social behavior, not interspecies mutualisms.
- A key question is whether hosts evolve costly punishment to prevent symbiont cheating.
Purpose of the Study:
- To distinguish between partner fidelity feedback (PFF) and host sanctions (HS) as mechanisms maintaining mutualisms.
- To test the hypothesis that costly punishment (HS) is necessary for mutualism stability.
- To investigate the evolutionary origins and prevalence of cheating prevention strategies in mutualisms.
Main Methods:
- Formulated a coevolutionary model of mutualism using economic employment contract theory.
- Distinguished between PFF (positive feedback) and HS (costly punishment) mechanisms.
- Analyzed published data from legume-rhizobia and yucca-moth mutualisms.
Main Results:
- Host sanctions (HS) are unlikely to evolve de novo.
- Data from legume-rhizobia and yucca-moth systems support PFF, not HS.
- Partner fidelity feedback (PFF) can stabilize even horizontally transmitted mutualisms.
Conclusions:
- Costly punishment (host sanctions) is not a ubiquitous or necessary mechanism for maintaining mutualisms.
- Partner fidelity feedback (PFF) provides a sufficient mechanism for stabilizing mutualisms, including those with horizontal transmission.
- PFF theory imposes constraints on the evolution of mutualism and helps explain the rarity of punishment in nature.
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