Symbiont Choice in the Attine Ant-Fungus Mutualism

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A major unresolved problem in biology is explaining the maintenance of cooperation and mutualism. One unstudied mechanism that stabilizes mutualisms between species is partner choice, where one of the mutualists discriminates between superior versus inferior partners, and rewards the superior types through preferential association. This proposal develops the attine ant-fungus mutualism as a model for the study of symbiont choice. Attine ants cultivate monocultures of fungal clones as their major food source, whereas the fungus receives from the ants both nourishment and protection from pathogens. The proposal develops several ant-fungus systems, including leafcutter ants from the southwestern USA, to study the genetic consequences of symbiont choice exerted by the ants on their fungi. In essence, the proposed experiments ask whether cultivar diversity in ant gardens, arising through genetic mutation, may evolve under an analog of ant-driven "artificial selection" (symbiont choice).Because symbiosis is a major recurring theme in the history of life, this research is expected to generate insights into the mechanisms that drive biological complexity and diversity. Such insights could impact issues directly relevant to human welfare, including disease evolution and the practice of sustainable agriculture. The case study of the attine ant-fungus mutualism will also be used to promote education of students and the public on the importance of ecological, symbiotic, and ultimately all biological processes.