Evolution

Crop Rotation

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Science  04 Apr 2008:
Vol. 320, Issue 5872, pp. 21
DOI: 10.1126/science.320.5872.21c

Humans, attine ants, termites, and bark beetles have one thing in common—they all practice agriculture. The attine ants are found in the neotropics in South America; they grow and harvest fungal cultivars; and they co-opt a filamentous bacterium, which produces an antibiotic, to help control a parasitic fungal “crop disease.” Schultz and Brady have calculated a fossil-calibrated molecular phylogeny of the attine ants and suggest that agriculture arose only once, as it did in termites, and unlike in humans or bark beetles, where it evolved independently several times. From this single emergence, five distinct agricultural systems developed, with the most primitive appearing roughly 50 million years ago. A radically different fungal cultivar, coral fungus, was adopted later by some ant species, and in a third offshoot, the normally filamentous Leucocoprineae fungi, common to most of the attines, were instead grown as nodules of single-celled yeast by select species. Further evidence for adaptive domestication of their fungal crop is seen in the ant species (including the leaf-cutter ants) that carry out higher agriculture: These fungal cultivars cannot survive independently of the ants, unlike those cultivated under the other systems, and these fungi produce gongylidia—swollen nutritious hyphal tips harvested by their caretakers. — GR

Proc. Natl. Acad. Sci. U.S.A. 105, 10.1073/pnas.0711024105 (2008).

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