REVIEW: Evolution of supercolonies: The Argentine ants of southern Europe

Proc Natl Acad Sci U S A. 2002 Apr 30;99(9):6075-9. Epub 2002 Apr 16.

 As that clip illustrates, ants are serious stuff. People are suffering all over the world and sadly, Macgyver cannot be there for everyone. Those ants are such devastating monsters that corn-fed Americans all over the 50's feared THEM!!!

 Well, today's paper is all about normal sized ants, but Macgyver sized colonies. As many of you know, Linepithema humile (hereafter called ants) was transported from Argentina to southern Europe, as many ecological disasters are, on the back of trade (think rats, plague, kudzu, and Europeans).The interesting thing about ants that were transported to southern Europe is that instead of forming colonies that are hostile to one another, they formed a supercolony where no hostility exists and workers from one nest can move freely in other nests.

Robots represent the major ant supercolony in southern Europe.

  The question is: how did this supercolony form and what is the genetic basis of it? It was previously suggested that all variation associated with recognition was lost due to the bottleneck of being moved to Europe. This means that the initial recognition signal in ants moved to Europe became fixed and all subsequent ants from that colony could recognize one another no matter what. Genetically, this means that ants introduced to Europe are much less genetically diverse and if one compared the sequences of the DNA associated with recognition, they would find that across large distances there is very little genetic diversity. The investigators in this study decided to test two things:

1. Loss of genetic diversity of ant nests across large geographic distances.

2. Aggression of ant nests to colony members across large geographic distances.

 First, they collected 5,000 workers from 33 nests across the major supercolony territory and some in the minor supercolony called the Catalonian supercolony. With all these ants, they did the one thing that all young children love to do, they made them fight. Or rather they gave them a confined space and hoped they would fight. What they found was that ants within a nest did not fight each other. Ants from within the same supercolony did not fight each other. When ants from the Catalonian supercolony and the major supercolony were put together they fought. To the death and then some. From the intersupercolony cage battles, death was the result 98% of the time. So don't ever throw down with an ant.

 The ant fights really suggest that the antagonism between supercolonies might be genetic, so they picked 32 individuals from each sample site and extracted their genomic DNA and then sequenced several genes for comparison. The original idea was that there was a bottleneck of ants introduced into Europe and that is why variation at DNA sequences associated with recognition would be very low, but these researchers found something different. Their data suggests that there was a genetic bottleneck, but it was not severe enough to give the observed results.

 What could possibly explain these results if a genetic bottleneck is not the cause? They propose that there was a genetic cleansing of recognition sequences. This means that there was selection against different recognition sequences. They believe this to be the case because of several interesting pieces of evidence:
1. There was genetic difference at many sites between nests within a supercolony, but no antagonism between them.
2. Ants in Europe have a higher density of nests than in Argentina.
3. Non -aggressive, neighboring nests attained a higher number of workers.
 This evidence suggests that upon introduction into Europe the ants developed nests very close to one another and from constant contact with one another, there was positive selection for a loss of diversity at recognition sequences. THIS LEADS TO THE SUPERCOLONY!!!

 As the supercolony develops maybe the increased aggression between supecolonies will be selective for new strategies and tactics!! The battle would be waged using our fields and farms as the battle grounds!! Would it push for new ant classes? Poisonous ants? Permanent flying ants? Larger ants?

 What if the supercolonies learn commerce? They would team up and begin their destruction of humanity!! What if the ants enslaved other species?! Roaches and earthworms not harvested for food or labor, but for strategy against our infastructure!

 How could we defeat the ant menace? Constant pesticide? Viruses? Other invasive species? Just imagine the outback of Australia, but instead of rabbits there are ants.