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| Fire ant mounds are common on Texas lawns |
Such reckless behavior, which quickly identifies one as being "not from around these parts," would be an invitation for pain. That's because most of our lawns are patrolled by armies of fire ants (Solenopsis invicta), quick to defend their nests with their small but potent stings.
We try our best to kill them with poison baits, toxic chemical sprays, and (for the more ecologically minded) pots of boiling water. But they always seem to return, like Medusa's heads, in even greater numbers.
Why are fire ants so hard to kill?
As many people are aware, to kill an ant colony you must kill the queen. And the trouble with most of the fire ants here in Texas and in other parts of the South is that they often have more than one queen. Many, in fact.
Among ants, this is a fairly uncommon characteristic, but it comes with a number of interesting "side effects" that have been noted by biologists. Colonies with multiple queens (known as "polygyne" colonies) tend to be smaller and more numerous in a given patch of land, like a lawn. The queens are also smaller, on average, and don't fly away to mate like their single-queen cousins.
Instead, when queens decide to leave home to start their own colony, they leave the nest on foot and bring a few workers with them. They might even join forces with other queens, setting up the new nest together. It's no problem if the new nest happens to be near an established ant mound, even the one they came from-- unlike in single-queen colonies, polygyne workers are tolerant of their fellow fire ant neighbors.
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| Red imported fire ant workers surround a winged queen |
Researchers have known for a decade or so that there is a genetic difference between queens in polygyne colonies and those in single-queen colonies. A single gene, called Gp-9, was identified by Laurent Keller and Kenneth Ross in 1998 that determines the social form (polygyne or not) of a fire ant queen. What couldn't be explained is how this single gene, which codes for a pheromone-binding protein, could be responsible for so many different physical traits and behaviors as observed between single-queen and polygyne colonies.
Today, a study published by John Wang and colleagues in the journal Nature explains the answer. Gp-9, it turns out, is just one of many genes that are located on what the authors call a "social chromosome" in fire ants.
In much the same way that multiple genes are packaged together on the Y chromosome in human males, and are together responsible for the many physical traits and behaviors that distinguish men from women, so too do these genes synergistically create the polygyne syndrome in fire ants.
The social chromosome even shares similarities with the human Y chromosome (and the sex chromosomes of animals), such as not recombining with other chromosomes the way most genes do. Such recombination, which shuffles genes around to create new and sometimes useful combinations, would not work well with sex-related traits since the traits need to stay associated with a particular sex. So strategies have evolved that prevent this from happening in sex chromosomes, and similar mechanisms appear to exist in the social chromosome of fire ants.
Highly social organisms like ants have always fascinated us, and researchers have been interested for decades in the genetic basis for sociality in its various forms. This study is the first to document the existence of a social chromosome, but it is not likely to be the last.
It seems we may be on the verge of deciphering the fascinating secrets behind the social lives of insects, which will have the potential to help us finally understand the evolutionary basis of complex behaviors. It may even help us control pest species like fire ants, whose success is due in large part to their unusual ability to cooperate.
For now, though, I'd stay off the lawn.
Photos by Alex Wild (http://www.alexanderwild.com)
