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.
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