FUNGUS-growing ants are far more sophisticated and enterprising farmers than
previously thought. After analysing fungi from hundreds of nests, researchers
have concluded that ants continually introduce new varieties of fungus into
their colonies.
Ants became farmers about 50 million years before humans. They can鈥檛 digest
the cellulose in leaves, but fungi can. So some ant species encourage a fungus
to grow on the leaves they collect and feed on it instead. Over time, their
farming system has become extremely complex鈥攖hey grow fungi in their
nests, secrete antibiotics to control other fungi and spread their waste as
fertiliser to maximise their yields.
Until now, scientists have assumed that one ancient type of fungus co-evolved
closely with its ant hosts. But Ulrich Mueller of the University of Maryland at
College Park and his colleagues have found that farmer ants are more creative
than we have given them credit for. Mueller鈥檚 team genetically screened 862
types of fungi taken from nests, as well as related wild fungi. 鈥淲hat they
cultivate is a surprisingly complex array of fungi,鈥� he says.
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Their analysis shows that ants have repeatedly domesticated new species, some
quite recently. DNA sequences from some ant crops, for instance, exactly matched
the wild-type fungi, which strongly suggests recent introduction, says Mueller.
Rather than a single domestication long ago, as entomologists previously
assumed, the genetic evidence suggests at least six independent domestications
(Science, vol 281, p 2034), but there may have been many more.
The researchers also noticed that some fungi were found in geographically
surprising patterns. They think that ants may swap crops with their neighbours.
The DNA analyses suggest that cultivar sharing occurred at least seven times
between ants of the same genus and four times between more distantly related
ants.
鈥淐learly in ants, the introduction of agriculture was unconscious,鈥� says
animal behaviourist Jared Diamond of the University of California School of
Medicine in Los Angeles. 鈥淔ive ants didn鈥檛 sit down and say: `We鈥檙e sick of
being picked off by warblers, let鈥檚 farm mushrooms鈥�.鈥�
However, Diamond thinks this discovery about ants may influence the debate
over the origin of human agriculture. 鈥淚t鈥檚 plausible that it was unconscious
for humans as well.鈥�