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European Union for Ants: supercolony reigns from Italy to Portugal. (This Week).

Researchers have documented the largest ant supercolony yet, a network of Argentine ant The Argentine ant (Linepithema humile, formerly Iridomyrmex humilis) is a tiny dark ant native to northern Argentina, Uruguay, Paraguay, and southern Brazil.  nests stretching at least 6,000 kilometers across Europe.

It's "the largest cooperative unit ever recorded," says Laurent Keller of the University of Lausanne The University of Lausanne (in French: Universit├ę de Lausanne) or UNIL in Lausanne, Switzerland was founded in 1537 as a school of theology, before being made a university in 1890. Today about 10,000 students and 2200 researchers study and work at the university.  in Switzerland. He and his colleagues describe the supercolony and a smaller, separate supercolony of the ants in Spain in an upcoming Proceedings of the National Academy of Sciences The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United States National Academy of Sciences. .

Just how a supercolony forms has long puzzled biologists, Keller says. Back in the ant's native range in and around Argentina, the species, Linepithema humile, doesn't seem cooperative at all. Colonies stay small, and workers clash violently with neighbors of the same species.

However, along much of the California coast, Argentine ants treat each other like family, according to according to
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

 a 2000 study by Nell Tsutsui of the University of California, Davis The University of California, Davis, commonly known as UC Davis, is one of the ten campuses of the University of California, and was established as the University Farm in 1905. . "You can take ants from San Diego San Diego (săn dēā`gō), city (1990 pop. 1,110,549), seat of San Diego co., S Calif., on San Diego Bay; inc. 1850. San Diego includes the unincorporated communities of La Jolla and Spring Valley. Coronado is across the bay.  and drive them to a colony in San Francisco San Francisco (săn frănsĭs`kō), city (1990 pop. 723,959), coextensive with San Francisco co., W Calif., on the tip of a peninsula between the Pacific Ocean and San Francisco Bay, which are connected by the strait known as the Golden , and they'll act like they've known each other all their lives," says Tsutsui.

He and his coworkers compared genetic diversity in the California ants with diversity in their South American cohorts. At specific test points in the genomes, the California ants showed about half as much diversity in their DNA sequences.

The ants' adoption of a laid-back lifestyle in California could have come from passing through a so-called genetic bottleneck, the researchers proposed. The supercolony may have emerged from just a few far-flung Argentine ants, resulting in enormous populations of ants so genetically similar that even widely separated members respond as if everybody's from the same nest.

To see how Argentine ants fared when invading Europe, Keller and his colleagues collected ants from 33 spots along the coast from northern Italy Northern Italy comprises of two areas belonging to NUTS level 1:
  • North-West (Nord-Ovest): Aosta Valley, Piedmont, Lombardy, Liguria
  • North-East (Nord-Est): Friuli-Venezia Giulia, Veneto, Trentino-Alto Adige/S├╝dtirol, Emilia-Romagna
 to northwestern Spain. Out of more than 1,000 staged encounters between ants from various places, the majority ended peacefully--the hallmark of a supercolony. However, certain pairings resulted in lethal fights. The researchers concluded that southern Europe actually hosts two supercolonies of Argentine ants.

"The study confirms that a lot of what we know from North America is going on in Europe," says Tsutsui.

The European study diverges from the North American North American

named after North America.

North American blastomycosis
see North American blastomycosis.

North American cattle tick
see boophilusannulatus.
 in its genetic findings. Keller and his colleagues report that European ants are only 28 percent less diverse genetically than those in South America. This reduction in diversity could have helped--but would not have been sufficient to--pave the way for a supercolony, Keller says.

That's why he and his colleagues propose that supercolonies developed through a process they call genetic cleansing. In a new territory away from old enemies, Argentine ants prospered and formed dense clusters of colonies. Genetically similar colonies, which could cooperate, wasted less time fighting and were more successful than the others, until a genetically more compatible supercolony emerged.

"It's an interesting and plausible hypothesis that needs to be tested," Tsutsui says.

Population biologist David Queller from Rice University in Houston says he has some questions about whether genetic cleansing would work. "If it's so advantageous to cooperate, why don't we see it more often?" asks Queller.
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Author:Milius, S.
Publication:Science News
Article Type:Brief Article
Geographic Code:4E
Date:Apr 20, 2002
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