( A study led by University of California...)Invasive ants territorial when neighbors are not kin

In the December issue of the journal Molecular Ecology, the biologists provide the first data on territorial interactions among Argentine ants in the field. In California, Argentine ants form expansive "supercolonies" containing millions of nests and stretching hundreds of miles. Researchers have disagreed on the reason for the lack of aggression between ants from different nests in the same colony.

"Some ecologists have hypothesized that environmental factors act to reduce aggression among Argentine ants in California," said David Holway, an assistant professor of biology at UCSD and senior author on the study. "However, we found that while ants from the same supercolony do not fight, clashes between ants from different supercolonies occur commonly along territorial borders."

The distance between nests did not play a role in ants' territorial behavior. Nor were there any obvious environmental clues to explain why ants would attack ants of the same species from one neighboring nest but not another. However, the researchers found a very close relationship between behavior and genetics. Ants that were genetically similar had peaceful relations. Ants that were genetically different attacked each other.

"Our results are strong evidence that lack of genetic diversity permits supercolonies to arise," said Melissa Thomas, who was a postdoctoral fellow working with Holway when she collected the data on territorial interactions. "Workers cannot differentiate between nestmates and non-nestmates if they all seem the same. So ants from different nests in the same colony do not fight with each other."

Five supercolonies of Argentine ants are known to occur in southern California.
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Source:University of California - San Diego