Symbiotic Nitrogen Fixation in the Fungus Gardens of Leaf-Cutter Ants

Gardening for Ants and Termites Among the social insects, ants and termites are the most diverse and ecologically dominant. Termites are known to engage in a mutualism with nitrogen-fixing bacteria, and Pinto-Tomás et al. (p. 1120 ) have identified similar relationships occurring among leaf-cutter ants, which maintain specialized nitrogen-fixing bacteria in their fungus gardens. Together, these mutualisms are a major source of nitrogen in terrestrial ecosystems. How is the evolutionary stability of such mutualistic cooperation maintained? Aanen et al. (p. 1103 ) show that the Termitomyces fungus cultured by termites remains highly related because mycelia of the same clone fuse together and grow more efficiently to out-compete rare clones.