Laboratory analysis by the UCSD team revealed that ants in Argentina had more than twice as much microsatellite variation in their DNA than ants from California. As a result of their greater genetic diversity, ants from different nests in Argentina do not recognize each other as family and therefore display territorial aggression, the researchers concluded.

But in California, all of the ants must be closely related because they're so genetically alike, according to the UCSD scientists. That would explain why California workers hardly ever fight with one another - even if they're from opposite ends of the state.

"We found that if ants are not genetically similar, they are typically aggressive toward each other," said Tsutsui, who is now on the faculty at the University of California-Irvine. He explained that the loss of genetic diversity in the California population probably began a century ago, when the state was invaded by a small population of Argentine ants whose offspring have continued to work cooperatively ever since.

"California's Argentine ants are very genetically similar, probably because they share a common ancestry," Tsutsui said. "There had to have been at least 10 mated queens in the founding population a century ago, but it could have been much larger. It would be as if all of the people in the United States were descended from the Pilgrims who came here in 1620."

Instead of fighting, Tsutsui explained, each new generation of California ants works as a team - gathering food, wiping out competitors and building new nests year after year. The result: an enormous supercolony that currently extends from San Diego to Ukiah.

These findings "suggest a possible control strategy for the Argentine ant," Tsutsui and his co-authors wrote in PNAS. Their proposal: Consider introducing genetically unrelated colonies of Argentine ants into Californi
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Contact: Dawn Levy
dawnlevy@stanford.edu
650-725-1944
Stanford University
7-Apr-2004