CORVALLIS, Ore. - Humans have learned, in just the past few thousand years, how to identify seeds, plant a crop, fertilize the crop and help it grow, harvest it, store the food and eat it. We're quite proud of all this and consider these agricultural skills a cornerstone of our advanced civilization.

Ants, it appears, have been doing this for 50 million years.

In a new study published today in the journal Science, researchers have identified a fascinating path of evolution between a certain group of ants, a fungus they cultivate for food, and a parasite that can attack the fungi.

"This is one of the best studies to ever show such a complex co-evolution of different fungal and animal species that all depend on each other for their growth and survival," said Joe Spatafora, an associate professor of botany and plant pathology at Oregon State University.

"The parallels to the development of human agriculture are quite strong," Spatafora said. "And the battle for survival is like an arms race between these species, which has been going on for a very long time."

Spatafora participated in a project led by Cameron Currie at the University of Kansas, along with other colleagues at the Smithsonian Institute, University of Texas and U.S. Department of Agriculture. They studied leaf cutter ants, one of the major herbivores in tropical forests of the Western Hemisphere.

"These ants have a very organized social system," Spatafora said. "They bring plant material back to the nest and use it to feed and grow a pure culture of the fungus lepiotaceae, a family of mushrooms. They literally raise it as a crop, and build little chambers in their nest full of this fungus."

The fungus, in turn, produces specialized structures rich in lipids, which form the primary food of the ants. When it's necessary to establish a new colony, in some cases a queen ant carries some of the fungus with her in a special pouch that is part of her body. And there's evidence that through such careful management a single clone of this fungus may in some cases have been perpetuated for 20 million years.

"But it's not that easy," Spatafora said. "Parasites have also evolved to attack this process."

In this case, the enemy is escovopsis, a parasite that can significantly diminish the productivity of the fungus and even destroy an ant or fungal colony. It's a common and serious concern for the ants.

It's extremely unusual, the researchers say, to be able to track through such a distance of time the evolutionary adaptations that have allowed this combination of ants, fungi and parasites to "co-evolve" along with each other.

The National Science Foundation has recently initiated a new series of research initiatives called "Assembling the Tree of Life." The goal is to better understand and identify the evolutionary relationships of all the major groups of life on Earth.

"Fungi are one of the areas we know the least about," Spatafora said. "Fungi are the largest group of eukaryotic microbes and are the planet's primary decomposers of plant and other organic material. They're one of the most common life forms on Earth, but we haven't even named 90-95 percent of the species."

With a new $2.64 million grant from the NSF, Spatafora is leading a team of five laboratories at four institutions to address this concern. They are beginning work on assembling the "Fungal Tree of Life," and as part of that research, they will sample 1,500 species, sequence six genes, conduct DNA analysis, and generally create the most comprehensive study ever done of the evolution of fungi on Earth.

"This work will have both fundamental and practical applications," Spatafora said.

One of the major advantages of understanding evolutionary relationships is that it provides a predictive framework for studying other areas of biology. For example, many of our more important antibiotics come from fungi.

Understanding how the fungi that produce such beneficial compounds are related to other species provides a basis for screening other species for potential benefits as well, Spatafora said.

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Source: 

Joe Spatafora, 541-737-5304