Leaf-cutter ants are crafty cultivators. They tend vast gardens of fungus that they harvest to feed their minions. In return, the ants care for the fungus. They constantly clip and compost bits of leaves to form a rich substrate on which the fungus thrives. When the fungus is attacked by pathogens, the ants fight back, armed with bacteria that counteract the pathogen.
The fungus gardens the ants tend are complex communities. There are numerous interactions in the gardens, both symbiotic and parasitic. Scientists are just now starting to unravel the many complex connections that exist in an ant fungus garden. The latest discovery, made by Adrian Pinto-Tomas and colleagues, reveals that the fungal gardens tended by leaf-cutter ants are a haven for one of life's most basic processes: nitrogen fixation.
Nitrogen fixation is a chemical reaction essential for life. Microorganisms capture nitrogen from the atmosphere and convert it into a form that plants and animals can use. Without fixed nitrogen, organisms could not make the basic building blocks of life such as nucleotides and amino acids. Without nucleotides and amino acids there would be no DNA or proteins.
Pinto-Tomas' team noted that there was more fixed nitrogen in the fungus gardens than they expected. It appeared as if the fungus gardens were being enriched with extra fixed nitrogen. But where was this extra fixed nitrogen coming from? To answer this question, Pinto-Tomas and his colleagues set up a series of experiments.
They placed leaf cutter ant nests in airtight chambers that they then filled with a special mix of air. The air contained a type of nitrogen that they could trace through the system. After a few weeks, they found that fixed nitrogen was accumulating in the fungus garden. Pinto-Tomas and his team then set about looking for a microorganism that might be responsible for nitrogen fixation within the fungus garden. They found a strain of nitrogen-fixing bacteria known as Klebsiella. There was indeed nitrogen fixing afoot in the ants' fungal garden.
This research illustrates the amazing complexity of leaf-cutter ant fungus gardens. It also shows how advanced, how crafty, leaf-cutter ants are when it comes to cultivating fungus.
You can catch a glimpse of the inner workings of a leaf-cutter fungus farm here.
References
Pinto-Tomas, A., Anderson, M., Suen, G., Stevenson, D., Chu, F., Cleland, W., Weimer, P., & Currie, C. (2009). Symbiotic Nitrogen Fixation in the Fungus Gardens of Leaf-Cutter Ants Science, 326 (5956), 1120-1123 DOI: 10.1126/science.1173036
Photo courtesy Cameron Currie, © Science/AAAS.
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