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Farming techniques, not fungus, explain success of leafcutter ants

"Our findings suggest that several of the things we thought we 'knew' about leafcutters are not true," said researcher Scott Solomon.

By Brooks Hays
Farming techniques, not fungus, explain success of leafcutter ants
Leafcutter ants are the most sophisticated ant species, with colonies hosting unprecedented worker diversification and specialization. Photo by Brandon Martin/Rice University

May 9 (UPI) -- A comprehensive new survey has yielded new insights into the evolutionary success of leafcutter ants, the most advanced of the fungus-growing ants.

Leafcutter ants grow the largest colonies, featuring millions of ants, and produce the most diversified workforce. Until now, scientists have credited their fungus with the group's empowerment. But new research suggests the same fungus is cultivated by other less sophisticated ant species.

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It is a combination of unique -- but still poorly understood -- cultivation techniques that explains the evolution of the leafcutter ants, researchers argue in a new paper, published this week in the journal Molecular Ecology.

Genetic analysis of all 47 leafcutter ant species, from colonies and nests in Brazil, Texas and everywhere in-between, suggest the ants originated in South America. The findings also suggest the group has evolved alongside their fungal gardens.

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Unlike other fungus-growing ants, leafcutter ants can feed the fungus gardens with freshly cut leaves, not just decomposing bits. This has allowed the group to utilize a wider variety of vegetation and expand into a wider range of habitats -- diversifying, adapting.

But the new research showed the fungus grown by leafcutter ants is the same type of fungus grown by other ants. The ability of the fungus to turn fresh-cut leaves into nitrogen, the ants' energy source, is the result of cultivation methods employed by the ants.

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"The ability to grow domesticated crops was a major turning point in human history and evolution, and we thought, until recently, that a similar thing was true for leafcutters," Scott Solomon, an evolutionary biologist at Rice University, said in a news release. "Our findings suggest that several of the things we thought we 'knew' about leafcutters are not true."

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Rather than being the fungus itself that inspired the complexities of the leafcutter ant colonies -- characterized by a diversified workforce and nests that are sometimes large enough to be seen by space -- it is a unique combination of genetic variations and gardening techniques that explains their success.

"It's not the crop that makes them special," said Ulrich Mueller, a researcher at the University of Texas. "We found that leafcutter ants and their fungi have co-evolved, and while that's not a surprise, the evidence suggests that this co-evolution occurred in a more complex way than previously believed."

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