Single Gene Dictates Ant Society

Pheromone power. Monogyne workers tending their queen possibly have more sensitive pheromone receptors than do some polygynes.

Genes regulating behavior are very hard to pinpoint; even basic behaviors are thought to be influenced by many genes interacting in mysterious ways. But fire ant researchers at the University of Georgia say they've characterized a gene that may single-handedly determine a complex social behavior: whether a colony will have one or many queens. The gene in question seems to work by controlling how ants perceive pheromones that tell them who's a queen and who isn't.

Fire ants have two basic kinds of social organization. A so-called monogyne queen establishes a colony after going off on her mating flight, nourishing her eggs with her own fat reserves, without worker help, until they hatch and become workers themselves. Polygyne queens, in contrast, aren't considered as robust, fat, and "queenly" as monogynes, and they need worker aid to set up new colonies. Monogyne communities only permit a single queen, and kill would-be queen intruders; polygyne colonies can contain anywhere from two to 200 queens, and accept new queens from nearby nests.

All these differences, suggest biologists Michael Krieger and Kenneth Ross of the University of Georgia, Athens, depend on which version of a gene known as Gp-9 ants possess, the researchers report in Science online 15 November. The gene encodes a pheromone-binding protein that may be crucial for recognizing fellow fire ants. Genetic tests revealed that all ants in a monogyne colony have two copies of the B allele, but among the polygynes, at least 10% are heterozygous, carrying a mutant allele, b, which Krieger says appears to code for a faulty protein.

Although polygyne communities kill potential BB queens, the Bb proportion of the colony somehow "persuades" the rest to accept Bb queens, says Krieger. These queens apparently escape attack, Krieger explains, because they are less "queenly" than BB queens and the Bb workers--which have the defective pheromone receptor--have trouble recognizing them.

The research "opens up for the first time the study of genes influencing social behavior across the whole span of the biological hierarchy," says Andrew Bourke of the Zoological Society of London, "from the most basic, molecular level, through the level of individual behavior, right up to the social level."

Related sites

Kenneth Ross's home page
Andrew Bourke's home page
More on fire ants

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