Approximately 50 million years ago, some Amazonian ant species discovered that raising fungi could provide a more stable food source than just foraging on the rainforest floor. Thus, they became farmers. Now, more than 200 species of New World ants cultivate crops, fastidiously fertilizing, cleaning, and weeding delicate white fungal filaments in their underground lairs. And, like human farmers who exchanged ancient emmer wheat for modern varieties, these ants have updated the crops they grow over time, according to new research.
In an attempt to reconstruct the ant's and fungi’s evolutionary history, evolutionary biologist Alexander Mikheyev of the Okinawa Institute of Science and Technology in Japan and colleagues looked at molecular clocks—accumulations of mutations in short stretches of DNA that reveal when a species diverged from its ancestors—for both organisms. The team found that the fungi were evolving at vastly different times than the ants. For instance, leaf-cutter ants diverged from their ancestors 12 million years ago, but the fungus that they cultivate arose only 2 million to 3 million years ago. Rather than evolving in step, the ants must have domesticated a new fungal strain, which spread through the ants’ range and eliminated any trace of the previous cultivar, the researchers report in the June issue of The American Naturalist.
Such a result is not entirely surprising, says Mikheyev. It is roughly analogous to human farmers switching one crop for another and, as he points out, human evolution is not tied to our cultivars. “In retrospect, it’s almost blindingly obvious that this should be happening."
Mycologist Bryn Dentinger of the University of Minnesota, Twin Cities, says that the results add “another level of complexity” to the coevolution of the ants and fungi. But he cautions that the evolutionary history of fungi is still poorly understood, and the results will have to be updated as scientists discover new fungal species.
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