The genetic basis for animal social organization is poorly understood. Fire ants provide one of the rare cases where variation in social organization has been demonstrated to be under genetic control, which amazingly, segregates as a single Mendelian locus. A recent genetic, genomic, and cytological analysis revealed that this locus actually consists of over 600 genes locked together in a supergene that possesses many characteristics of sex chromosomes. The fire ant social supergene also behaves selfishly, and an interesting evolutionary question (...) is whether the genes incorporated first into the social supergene were those for social adaptation, selfish genetic drive, or something else. In depth, functional molecular genetic analysis in fire ants and comparative genomics in other closely related socially polymorphic species will be required to resolve this question.Editor's suggested further reading in BioEssays Social supergenes of superorganisms: Do supergenes play important roles in social evolution? Abstract. (shrink)

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. (shrink)