Abstract

A major distinction in the social organization of ant societies is the number of reproductive queens that reside in a single colony. The fire ant Solenopsis invicta exists in two distinct social forms, one with colonies headed by a single reproductive queen and the other containing several to hundreds of egg‐laying queens. This variation in social organization has been shown to be associated with genotypes at the gene Gp‐9. Specifically, single‐queen colonies have only the B allelic variant of this gene, whereas multiple‐queen colonies always have the b variant as well. Subsequent studies revealed that Gp‐9 shares the highest sequence similarity with genes encoding pheromone‐binding proteins (PBPs). In other insects, PBPs serve as central molecular components in the process of chemical recognition of conspecifics. Fire ant workers regulate the number of egg‐laying queens in a colony by accepting queens that produce appropriate chemical signals and destroying those that do not. The likely role of GP‐9 in chemoreception suggests that the essential distinction in colony queen number between the single and multiple‐queen form originates from differences in workers' abilities to recognize queens. Other, closely related fire ant species seem to regulate colony social organization in a similar fashion. BioEssays 27:91–99, 2005. © 2004 Wiley Periodicals, Inc.