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Are ants the original farmers?

Following Charles Darwin's and Alfred R. Wallace's independent publications of their evidence for evolution by natural selection in the mid 19th Century, many people interpreted their findings as indicating life was "red of tooth and claw." By this was meant that much of life seemed to be just an unending struggle between predators and their prey; as predators evolved to be stronger and bigger, their prey evolved to be better camouflaged and more nimble. This notion of life as simply a case of "survival of the fittest" became a horrendous argument (fortunately, now discredited) for the euthanasia of those born physically or mentally compromised. Ironically, such a heartless approach remains the major tool of those engaged in breeding livestock and pets.

Research over the past century has shown, however, that evolution is much more complicated than the words "survival of the fittest" seem to convey. Species are no longer seen as so clearly independent of one another and they often survive only because of highly complex and mutually beneficial interactions with other, quite different, organisms.

Fascinating examples of this complexity are those shown by a number of species of fungus-growing ants, termites, beetles, and snails. For instance, beginning at least 50 million years ago these species of ants have been cultivating fungi and most of these fungi do not occur outside the nests of these ants. Furthermore, many of the fungi involved rarely fruit but have, instead, evolved specialized swellings rich in fats and carbohydrates upon which the ants feed. Different species of ants grow their particular species of fungus on different substrates. Some use insect feces, some dead plants, some wood, and some use bits of leaves cut from living vegetation by worker ants (the leaf-cutter ants).

Like all gardens, these fungal gardens need constant care and worker ants are kept busy weeding their underground crops of unwanted fungi. But, like humans, this is not their only defense against the invasion of pathogens which threaten their food supply. At least some ant species also inoculate their fungal gardens with bacteria that secrete an antibiotic capable of eliminating a highly pathogenic mold that can destroy their fungal gardens. These antibiotic-producing bacteria are carried around by the ants in special pouches and are easily transported to new nests. Thus, in this setting, three unrelated species, the ant, their fungal food, and this bacterium, are working together to ensure their mutual survival.

But these may not be the most ancient farmers, and certainly not the smallest. Recently, a single-celled organism that feeds on bacteria has been observed "planting" bacteria along with its spores in order to ensure the next generation has food to harvest in its new environment.

Questions and suggestions from readers are welcomed and will be responded to in future editions of this column. Contact me at cwdingman@frontiernet.net.

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