Plasticity in caste-related exocrine secretion biosynthesis in the honey bee (Apis mellifera)

Plasticity of Dufour's gland secretion in the honey bee is correlated with the individual's plasticity. Queens and queenless (QL) egg-laying workers possess a bouquet of esters and hydrocarbons, whereas queenright (QR) workers produce exclusively hydrocarbons. The effects of social environment (QR vs. QL conditions) and possible physiological constraints on the gland were studied by following the biosynthesis of these classes of compounds in vivo and in vitro. Biosynthesis in vivo followed the prediction based on glandular chemistry. Queens and QL egg-laying workers, but not QR workers or QL foragers, showed incorporation of sodium acetate into both hydrocarbons and esters. In contrast, the in vitro studies revealed that, in addition to queens and QL egg-laying workers, QR nurses retained their ability to produce the queen characteristic esters. Although there was some ester production in foragers, it occurred to a lesser extent. It is possible that the glands in the older foragers undergo irreversible changes. The in vitro incubation also revealed a temporal activation of ester biosynthesis in QR workers. In these glands alcohols, corresponding to the alcohol moiety of the esters, predominated in short-term incubations but decreased as the amount of newly synthesized esters increased. In contrast, queens and QL egg-laying workers showed predominant incorporation into esters from the onset of incubation. Thus, expression within the workers' Dufour's gland is regulated. In the presence of a queen, ester production is inhibited. Once the queen is removed the physiologically unconstrained gland starts to biosynthesize the queen-specific esters after a certain lag needed for the build-up of precursors and the enzymatic machinery.