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Ant "Supercolony" in Europe Raises Questions About Getting Along |
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Bijal Trivedi National Geographic Today |
| Updated April 23, 2002 |
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Squabbling parties within the European Union could learn a lot about how to get along from the invasive Argentine ant population. Researchers have discovered an enormous "supercolony" of these ants that extends across 6,000 kilometers (3,728 miles) of Southern Europe. All the ants within this supercolony, even those from different nests, seem to behave amicably toward each other. This is the largest cooperative biological unit ever discovered. By contrast, in Argentina, ants from different nests are particularly belligerent and fight to the death, says Laurent Keller, an entomologist from the University of Lausanne, Switzerland, who led a study on their behavior. Keller's team captured about 5,000 ants from 33 separate nests in Italy, France, Spain, and Portugal and transported the insects back to his laboratory. Once in the lab, the scientists arranged ant fights—pitting ants from one nest against ants from the other 32 nests. Over the span of a year, the scientists conducted almost 1,100 ant fights. What they discovered was that all the ants were members of either one of two enormous supercolonies. A supercolony is a remarkable structure because it involves hundreds of billions of individuals. Ants from 30 of the nests belonged to the main supercolony, which stretches from northern Italy along the Mediterranean coastline past France and Spain and curves around the Iberian Peninsula past Portugal. Ants from three Spanish nests represented a smaller Catalonian supercolony. Defying Expectations What is extraordinary is that ants from nests separated by thousands of kilometers did not show any aggressive tendencies towards each other; ants from Portugal, Spain, Italy and France all got along, says Keller. What has scientists befuddled is how a supercolony arises. The whole concept of these large colonies clashes with the "kin selection theory," which basically predicts that altruistic behavior should only occur between related individuals. But within the European colony, a visiting ant from the Portuguese branch of the supercolony, for example, is just as welcome in an Italian nest as a local ant. A possible explanation was that the entire supercolony arose from a very small number of founders, which would mean that the ants within the colony are genetically very similar—hence their surprising tolerance of ants from distant nests. But this did not prove to be true. A genetic analysis done by Keller's team revealed that the European Argentine ants are a diverse lot. "It's a very nice piece of work," says Kenneth Ross, an entomologist from the University of Georgia, in Athens. "Keller and his colleagues collected a huge number of samples, tested many genetic markers and proved that this tolerance is not due to these ants being closely related." Keller's work is published in the April 16 issue of the Proceedings of the National Academy of Sciences. Adaptive Behavior It seems that when the Argentine ants invaded Europe in 1920 they entered a "bonanza habitat," says Ross. Ross suspects that with plentiful food and no natural enemies, defending territory and fighting unrelated ants was no longer necessary for survival. "Nest mates or not, why fight if there is plenty of food," says Ross. Thus genes involved with recognition—those that allow ants to distinguish a nest mate from a foreigner—may have been less important and lost over time, says Ross. Keller agrees that there has been a "genetic cleansing" of the recognition cues—the genes involved with recognition must have become very similar within each ant supercolony. What is clear is that the recognition genes between the main European supercolony and the Catalonian supercolony are very different. Ants from these colonies fight aggressively—biting at the head, releasing venom and locking body parts in the jaws. Death usually occurs within a minute. "What I find exciting is that the social organization of an entire species can change by changing environment," says Keller. Argentine ants are a particularly aggressive invasive species. Away from their homeland they tend to displace or eradicate the local ant populations as well as spiders and insects. The ants destroy fruit and buds, and tend to protect insects that devastate plant life. Their tremendous destructive power is due in part to their ability to form these vast cooperative colonies. National Geographic Today, at 7 pm. ET/PT in the United States, is a daily news magazine available only on the National Geographic Channel. Click here to request it. 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