Hydrocarbons aid ants in queen worship

Gas chromatography reveals why worker ants destroy their eggs.

Ant societies hold a particular fascination for us disorganised humans. Some worker ants have a peculiar habit of destroying the eggs of their own kind while preserving those of their queens. Now an Anglo-German team of researchers has discovered that worker ants distinguish between their eggs and those of queen ants through simple hydrocarbons.

Researchers from Wurzburg University, Germany, and from the chemical ecology group at Keele University, UK, studied Camponotus floridanus ants from Florida. In this species, a single queen lays eggs while the majority of workers remains infertile. The research team found that the presence of queen-laid eggs induces worker ants to refrain from reproducing.

The team suspected that the key to the unusual contraception lay in the hydrocarbon waxes that coat the ants’ shells (or cuticles) to give them waterproof qualities. Graeme Jones, one of the Keele researchers, explains that ’in social insects such as ants, the hydrocarbons are like a uniform that tell other individuals about themselves, where they come from, what they do and sometimes where their parents come from’. The ants make up a profile using mixtures of hydrocarbons, which are mainly linear alkanes, methyl branched alkanes and dimethyl branched alkanes, Jones notes.

The researchers collected queens of C. floridanus at the Florida Keys, US, after the mating flight and transferred the ants to the laboratory. Over the following year, they report, the colonies grew to 1000-2000 individuals.

The team then extracted the hydrocarbons from queen and worker ants using hexane. They faked queen eggs by rolling worker-laid eggs in the hydrocarbon extracts using a solid-phase microextraction fibre. They also rubbed microextraction fibres on the shells of live ants before analysing their hydrocarbon profiles using GC-MS.

The worker ants destroyed eggs from sister workers but tolerated those from a queen. GC analysis revealed that queen-laid eggs differ from worker-laid eggs in the composition of their surface hydrocarbons, which are very similar to the hydrocarbons in the ants’ shells.

According to the research team, when the worker ants were given fake queen-laid eggs, ’the result was unequivocal’. The ants destroyed significantly fewer worker-laid eggs carrying the transferred queen hydrocarbon profile than worker-laid eggs. The team concludes that ’queen derived hydrocarbon labels inform workers about the presence of a fertile queen and thereby regulate worker reproduction’.

Emma Davies