concentrated during passage through the ant gut,
and are deposited in the fecal droplets. By cladistic
analysis of both the ants and their fungal associates,
Mueller & Gerardo have shown that the ability of ants
to cultivate fungi arose only once, about 50 – 60 mil-
lion years ago, but has given rise to about 200 species
of fungus-growing ants, matched to their specific fun-
gal associates.
An essentially similar type of behavior is found in a
subfamily (Macrotermitinae) of termites in Africa and
southeast Asia. Unlike most termites, this subfamily can-
not digest wood, because they do not have cellulolytic
protozoa in their guts. Instead they have evolved a sym-
biosis with the fungus Termitomyces(Basidiomycota)
which is cultured in fungus gardens, using plant debris
that is continually added to the colony. The termites
tend these gardens by weeding out any contaminant
fungi. After periods of heavy rainfall the fungus pro-
duces large, mushroom fruitbodies with long tapering
underground stalks. This association is highly special-
ized because Termitomycesspecies are only ever found
associated with termite nests.
A third association of this type is found in some wood-
boring beetles that produce tunnels in damaged or dead
trees. The beetles deposit eggs in these tunnels and
smear the tunnel walls with spores of fungi, collectively
known as ambrosia fungi. The spores of these fungi
are stored in special sacs (mycangia) on the beetle’s body
to provide inoculum for establishment in new sites.
The developing beetle larvae create extensive galleries
beneath the bark and feed predominantly, if not
exclusively, on the fungus. These “gardens” typically
contain only one type of fungus, because contaminant
fungi are weeded out.
There is a remarkable parallel in the evolution of these
three types of “fungus-farming” systems, because
about 40–60 million years ago the termites, ants, and
beetles independently evolved the ability to culture
fungi as their source of food. In ants and termites the
ability to culture fungi originated only once in each
group, but in ambrosia beetles it originated at least seven
times. Now all of these fungus-cultivating insects and
their fungal partners are mutually dependent on one
another. There is no evidence that they have ever
reverted to an independent existence.
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