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Evolution of Supercolonies: The Argentine Ants of Southern Europe
Tatiana Giraud, Jes S. Pedersen and Laurent Keller
Proceedings of the National Academy of Sciences of the United States of America
Vol. 99, No. 9 (Apr. 30, 2002), pp. 6075-6079
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/3058627
Page Count: 5
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Some ants have an extraordinary social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This type of social organization is not only a key attribute responsible for the ecological domination of these ants, but also an evolutionary paradox and a potential problem for kin selection theory because relatedness between nest mates is effectively zero. The introduction of the Argentine ant in Europe was apparently accompanied by a dramatic loss of inter-nest aggression and the formation of two immense supercolonies (which effectively are two unicolonial populations). Introduced populations experienced only limited loss of genetic diversity at neutral markers, indicating that the breakdown of recognition ability is unlikely to be merely due to a genetic bottleneck. Rather, we suggest that a "genetic cleansing" of recognition cues occurred after introduction. Indeed workers of the same supercolony are never aggressive to each other despite the large geographical distance and considerable genetic differentiation between sampling sites. By contrast, aggression is invariably extremely high between the two supercolonies, indicating that they have become fixed for different recognition alleles. The main supercolony, which ranges over 6,000 km from Italy to the Spanish Atlantic coast, effectively forms the largest cooperative unit ever recorded.
Proceedings of the National Academy of Sciences of the United States of America © 2002 National Academy of Sciences