Aggression studies reveal the existence of ant supercolonies   
By Kate Dalke 
April 26, 2002
 
Scientists have identified two distinct supercolonies of Argentine ants
in Europe. The main supercolony includes millions of nests comprising
billions of workers; it extends more than 6,000 kilometers along the
coastline of Italy, France, Spain, and Portugal and is the largest
cooperative unit ever recorded in nature, according to the researchers.
Argentine ant (Linepithema humile) workers from the two European
supercolonies invariably fight with each other. Death of one of the
protagonists usually occurs within one minute after the onset of the
fight. 
Photography by Charles König. 

The two supercolonies—known as the Catalonian and the main
supercolony—were identified based on aggression tests with ants in the
laboratory. When workers from different nests were placed in glass jars,
individuals of the same supercolony were never aggressive to each other,
while the level of aggression between ants of the two different
supercolonies was always high. 

The fact that members of the same supercolony from distant nests were
friendly "is particularly striking because workers came from populations
up to 6,000 km apart, which encompass a wide range of environmental
conditions," the researchers write in Proceedings of the National
Academy of Sciences.

Given the severe aggression typically seen in ants from different nests,
the researchers have developed theories to explain the workers'
different responses to ants of the same or the different supercolony. 

The genetic background of worker ants is a primary factor in determining
how aggressive they are to other ants, according to Laurent Keller, of
the University of Lausanne, Switzerland, who led the study. 

Keller's team has not yet identified specific genes involved in
recognizing members of the same supercolony, but that will be a focus of
future research. The idea is that differences in the genome may lead to
different responses and recognition among related and unrelated ants.
The researchers will also evaluate the role of the environment in ant
behavior.

The importance of ants to the economy and their unusual social
organization make the species a good candidate to be sequenced, says
Keller. Since its accidental introduction to Europe, the Argentine ant
Linepithema humile has been a successful and pesky invader. It displaces
local fauna, protects insects that destroy plants and fruits, and
invades homes. 
"Although progress in ant genomics is being made, little is still known
about the ant genome," says Keller.

 
Giraud, T. et al. Evolution of supercolonies: The Argentine ants of
southern Europe. PNAS Early Edition. Published online April 16, 2002.
 

"It's uncertain whether intelligence has any long term survival value.
Bacteria do quite well with it."

Stephen Hawking
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