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A big queen of the imported red fire ant Solenopsis invicta is tended by workers.
EPA.

This ant (Should we say "aunt?") is a social insect where sisterhood is indeed powerful since it involves thousands of sisters each equipped with two claws and one nasty stinger.

Fire ants attack insects, children -- indeed any animal that threatens its nest.

For severe stereotyping of social status, the imported red fire ant (Solenopsis invicta) rivals the Taliban, but in reverse. Females do the shopping, the soldiering, and (no duh!) the heavy lifting of reproduction. Ants unlucky enough to be born male will be called "drone" and their short lives end abruptly after their mating flights.

In fire ant colonies, the number of queens largely determines behavior and social structure. Now scientists have learned that one gene seems to influence the behavior that determines the number of queens in a colony.

It is apparently the first gene that determines complex social behavior.

In the 1920s, fire ants hitchhiked from their native South America to the southern United States, and later made a second long-distance jump to California. The nasty ants now live in parts of 14 states.

Counting queens
Michael Krieger, an entomologist at the University of Georgia, says the presence of one ("monogyne") or several ("polygyne") queens determines many aspects of social behavior. Lone queens, for example, are fat enough to feed a new colony by themselves, so they can start new, remote colonies and feed the workers until they can start gathering food.

Multiple queens are skinny by comparison, so they must take along some workers to feed a new colony, which will be only a few yards away from the parent colony. These colonies are satellites of the main nest that help form super-colonies with dozens of queens and an army of females packing more wallop than Elizabeth Cady Stanton and Susan B. Anthony combined.

The number of queens also matters when queens try to join an established colony. Polygyne colonies are generally open to adopting polygyne (but not monogyne) queens. But any queen that tries to enter a one-queen colony gets dismembered faster than you can mumble "Marie Antoinette."

Ants wear genes
What controls the number of queens in fire-ant colonies? Krieger thinks it's the sequence of a gene called Gp-9.

Krieger used a new "bassackwards" technique to find the gene. Instead of laboriously combing the ant's genome, he built on previous research by colleague Kenneth Ross, who had located a protein that seems to determine queen number, and then deciphered the sequence of the gene that would make that protein.

"My work was to isolate the protein, sequence the protein and then the DNA to see what type of gene it was, and then infer its function," Krieger says. A genetic database suggested that the gene was involved in binding pheromones, chemical signals that animals use to regulate mating and other behavior.

The protein takes part in a chemical recognition system that allows workers to recognize and accept "their" queen, leaving them free to attack other queens. While studying wild ants, Krieger found a perfect association between the form of the gene and the presence of single or multiple queens. The gene, he says, is the first known to have such a fundamental role in social behavior.

Fire ants crawling on board: USDA.

Once you step from ants to higher organisms, the relationship between genes and behavior gets a lot more complicated, intriguing and controversial. But on a practical level, because the pheromone in question protects ants from assault, the discovery could lead to a way to sting fire ants worse than they sting us.

"If you could create a compound that binds irreversibly to this odorant binding molecule, you could confuse them tremendously," says Krieger. "They would get a mistaken nerve signal that could lead to killing the sisters [workers] or even the queen." Lacking a queen, the colony could die of old age.
-- David Tenenbaum

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