Fungus-farming insects: multiple origins and diverse evolutionary histories.

A 40–60 million years before the advent of human agriculture, three insect lineages, termites, ants, and beetles, independently evolved the ability to grow fungi for food. Like humans, the insect farmers became dependent on cultivated crops for food and developed task-partitioned societies cooperating in gigantic agricultural enterprises. Agricultural life ultimately enabled all of these insect farmers to rise to major ecological importance. Indeed, the fungus-growing termites of the Old World, the fungus-growing ants of the New World, and the cosmopolitan, fungusgrowing beetles are not only dominant players in natural ecosystems, but they are also major agriculture, forestry, and household pests (1). Not surprising, much is known about the extermination of these pest insects, but only recently have genetic techniques been applied to elucidate the evolutionary histories of these unique nonhuman agricultural systems. In a recent issue of PNAS, Aanen et al. (2) present such an evolutionary analysis for fungus-growing termites and their cultivated fungal crops, complementing similar analyses recently completed for fungusgrowing ants (3–6) and fungus-growing beetles (7–9) (Fig. 1 a–c). Aanen et al.’s methodology followed the same two-part analysis anthropologists have taken to unravel the histories of human agricultural societies and their various crops. First, they assessed the patterns of relatedness between cultivated crops and wild, undomesticated varieties; patterns revealed which crops were derived from common ancestral stocks and thus the number of independent domestication events. Second, they determined the relationships between independent farmer societies to infer common origins of agricultural practices. Even in the absence of a fossil (or archaeological) record, a juxtaposition of these two phylogenetic histories can reveal surprising details of agricultural evolution.