he cellulose and chitin, materials that the ants cannot digest. The higher attines can then gorge themselves on the nutritious swellings of the fungus, the protein- and sugar-rich knobs called gongylidia, that bud off from the ends of the fungus, while lower attines generally feed on unmodified fungal hyphae (Ariniello, 1999). The attines comprise about 200 described species in 12 genera, all of which are dependent on fungiculture for food (Currie, Mueller and Malloch, 1999). Extant species cultivate multiple, phylogenetically distant lineages of fungi, mostly belonging to the family Lepiotaceae. These fungi used to exist in the caps of mushrooms, but in becoming symbiont with ants, the fungus has ceased making fruiting bodies to reproduce itself and instead has come to rely on the ants to spread their seed around (Angier, 1994). Queens propagate the fungus clonally by carrying a ball of fungus in their mouth when setting out to build a new nest, and the cultivars propagate vegetatively within nests. Although some lower attines propagate cultivars that were recently domesticated from free-living Lepiotaceae, the higher attines are thought to propagate ancient clones which may have been in existence for the past 25 million years (Angier, 1994). This means that every fungal garden found throughout South and Central America, where the ants thrive, is a descendant of a single ancestral spore.
A mature fungal garden may contain 8 million ants, ranging in size from the tiny garden tenders to the egg-swollen queen who may be the size of an unshelled peanut. Most of the nest is underground, with an elaborate labyrinth of passages and thousands of chambers ranging in size from that of a fist to the size of a soccer ball. To build such enormous nests, the ants must displace enough earth to fill a good-sized living room (Angier, 1994). The chambers are filled with the spongy gray hyphae of the fungus that feeds the entire colony....