Congruency of hydrocarbon patterns in heterospecific groups of ants: transfer and/or biosynthesis?

Abstract

In homospecific groups of ants, each species has its own hydrocarbon profile, on the epicuticle and in the postpharyngeal gland (PPG). When reared together in bispecific groups, workers of both species possess each other's hydrocarbons in both locations. The present study investigated two alternative mechanisms by which a mixed “odour” in artificial groups ofFormica selysi/Manica rubida can be created. Using [1-14C] sodium acetate as a precursor,de novo biosynthesis of hydrocarbons was demonstrated for both species whether reared in homospecific or mixed-species groups. The newly synthesized hydrocarbons occurred on the epicuticle, internally, and in particularly large amounts in the PPG. As expected from their PPG and epicuticular hydrocarbons composition, workersF. selysi synthesized alkanes and alkenes in comparable amounts irrespective of their rearing scheme. Likewise,M. rubida reared in bispecific groups synthesized mostly alkanes with only negligible amounts of alkenes, according to a ratio characteristic toM. rubida workers from homospecific groups and not toF. selysi workers. During dyadic encounters, a transfer of labeled hydrocarbons between nestmates (conspecific in homospecific groups and allospecific in mixed groups) was observed. These results suggest that the formation of the mixed hydrocarbon profile in artificial groups of ants is the result of a transfer of these chemicals between nestmates rather thande novo biosynthesis of the allospecific hydrocarbons. Behaviours like trophallaxis, grooming and body contact that occurred during the encounters mediated such a transfer.