Transcriptomic analysis of the mandibular gland genes associated with reproductive dominance in Apis mellifera capensis Esch. parasitic workers

Abstract

Regulation of reproductive division of labour is generally modulated by the queen's chemical secretions, particularly the mandibular gland (MG) pheromone complex. Workers can activate their ovaries and lay unfertilised eggs with some dominant workers able to produce queen-like MG signals to become false queens. We examined the effect of social condition as a regulator of social behaviour, by investigating differential gene expression in the MG of two subspecies of African honey bees, with differing reproductive potentials and, at two ages. Sequencing of RNA from young and older Apis mellifera scutellata (low reproductive potential) and A. m. capensis (higher reproductive potential) workers was carried out. A total of 5646 transcripts were differentially expressed across four libraries, classified into 29 biological processes based on their gene ontology accessions. Further, 48 differentially expressed genes were found to be putatively associated with the biosynthesis of MG fatty acids. Of these, 25 were cytochrome P450s thought to participate in the caste-specific hydroxylation of stearic acid, a crucial regulatory point in the biosynthetic pathway. Multiple points of regulation were identified starting from in-situ biosynthesis and activation of stearic acid, caste-specific hydroxylation, transport between organelles, uncompleted β-oxidation and oxidation of 9-hydroxy-2-decenoic acid (9-HDA) to 9-oxo-2 (E)-decenoic acid (9-ODA). Our data shows that regardless of age, reproductively dominant individuals switch on a very specific set of genes as they transition from worker-like to queen-like MG signals. This study provides insight into the molecular-level changes that occur as workers switch from social cooperative behaviours to reproductive dominance.