Project leader: N. Pierce (Harvard University)

Mutualisms involving cooperation between different species pose a special challenge to cooperation theory because they are commonly observed in nature but typically violate the assumptions of general cooperation models. There is still no generally accepted theoretical framework that explains how mutualisms evolve from antagonistic interactions, and then persist in the face of (a) invasion by parasites, or (b) selection for cheating behaviour among the mutualists themselves. However, many models and empirical results have been developed that explain the maintenance of cooperation within particular mutualistic systems. Based on these and other results, theory has for now settled on two basic explanations for the persistence of mutualism: partner fidelity and partner choice.

The project BIOCONTRACT aims to test and extend theory for two mechanisms that can produce cooperative associations between different species: (i) we are applying economic contract theory to a variety of well-characterised mutualisms and, (ii) we are testing empirically and extend spatial game theory in two radically different symbioses, those between ants and plants and those between plasmids and bacteria.