Parallel pheromone, metabolite, and lipid analyses reveal patterns associated with early life transitions and ovary activation in honey bee (Apis mellifera) queens

Abstract

Eusocial insects exist in a state of reproductive conflict in which workers forgo reproduction in favor of helping relatives, typically queens, rear offspring. The honest signal hypothesis posits that queens emit pheromonal signals that convey information about their fecundity, which workers use to make decisions around investing in direct vs. indirect fitness and queen acceptance. We evaluated this idea using liquid chromatography-tandem mass spectrometry to measure honey bee queen retinue pheromone (QRP) components in relation to queen age, laying status, and likelihood of acceptance using a protocol that enables QRP to be measured concurrently with metabolomic and lipidomic analyses. We found that older mated queens (>1 month) were more readily accepted by colonies than younger queens (10-12 d), regardless of the queens prior laying status. This is despite non-laying queens having significantly smaller ovaries at the time of introduction. Older queens produced higher levels of the QRP components 9(R)-HDA, LEA, and HVA compared to younger queens, with HVA also positively correlating with ovary mass. However, these data suggest that ovary mass is not an influential fertility metric for worker decision-making; therefore, the relationship between HVA and ovary mass is merely an honest signal of a non-influential metric. Metabolomic and lipidomic analyses showed that samples cluster strongly according to queen age and mating status, but not ovary mass. These data also reveal some of the first hints of the importance of prostanoids in queen maturation, along with many other physiological changes that occur in the first month of a queens life. Significance statementInsect pheromones have historically been evaluated using gas chromatography-mass spectrometry, a technique that is incompatible with parallel lipidomics and metabolomics inquests. Here, we repurposed an established two-phase extraction protocol and optimized a liquid chromatography-tandem mass spectrometry method to acquire pheromone, metabolite, and lipid data concurrently from a single sample. We applied this technique to interrogate the honest signal hypothesis, which relates queen pheromone profiles to reproductive quality, but the approach is broadly applicable to any question in which simultaneous determination of complex pheromone profiles and lipidomics or metabolomics data is asset. Such applications may help uncover new pheromones and reveal relationships between pheromones, hormones, and physiology in diverse biological systems.