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Tuesday "Noon" Seminar: Nov. 21Andreas Mathias on "Trade-offs Repel Temptation: Evolutionary Dynamics of Exploitation in the Rhizobia-Legume Mutualism"
12:30-1:45 p.m. in Biosciences West (map of building location), Room 208 |
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Talk Abstract Cooperation between unrelated organisms is thought to be difficult to maintain over evolutionary time because of the potential for exploiters to invade. Wild populations of rhizobia exhibit a range of life history strategies from highly mutualistic nitrogen fixers to parasitic non-fixing forms. The coexistence of these strains suggests that the ineffective strains are cheaters, as rhizobia inside root nodules fix atmospheric nitrogen at the expense of energy storage that could be directed toward survival when bacteria re-enter the soil. Although host plants can sanction ineffective nodules, they may not be able to discriminate between strains in mixed-infection nodules. These mixed nodules may thus provide a haven for non-fixing strains. We construct an evolutionary model of rhizobia strategy and find situations where the population becomes polymorphic through adaptive diversification of life history strategies driven by fitness conflicts between the symbionts and host. We also consider the case of within-nodule discrimination and find that the evolutionary system undergoes a bifurcation leading to a dramatic jump in the evolutionarily stable strategy. |
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