Market Dynamics in a Nitrogen-fixation Mutualism

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Nutritional symbioses between plants and soil microbes are critically important to plant evolution and ecosystem function, yet we know almost nothing about the evolutionary dynamics and mechanisms of persistence of these ancient interactions. Mutualistic interactions are widespread and obligatory for many organisms, yet their evolutionary persistence in the face of cheating is theoretically puzzling. Partner-choice and partner-fidelity are mechanisms for dealing with cheaters, and can theoretically allow mutualisms to persist. Evidence for sanctions against cheaters, a form of partner-choice, has recently been uncovered in several plant-pollinator interactions. Market models assume partner choice, and hence offer useful paradigms for understanding the evolutionary dynamics of mutualisms in which individuals attempt to conduct mutually beneficial trade of resources with multiple individuals (the market). The proposed studies will test whether partner-choice can explain the evolutionary persistence of this mutualism in wild legumes of the genus Lupinus, and Bradyrhizobium, the nitrogen-fixing bacteria that inhabit their root nodules. Achieving these goals is the first step in an integrated analysis of genetic variation, symbiotic quality, and plant adaptive responses in the legume-rhizobium interaction. Our results will begin to construct a framework for understanding the persistence and evolutionary dynamics of this important mutualism.