Threshold of defensive response in Apis mellifera (honey bees) and subsequent brain gene expression in reaction to noxious stimuli

Abstract

Honey bee, Apis mellifera L. (Hymenoptera: Apidae), colonies and individuals respond variably to disturbances. The response depends on perception and interpretation of stimuli requiring both neural modulation and use of energy. In this study, we examined the role of neural modulation and brain metabolism in constitutive and experiencedependent differences in defensive response. For constitutive differences, we compared brain gene expression in bees from gentle and defensive colonies identified in a standard colony-level assay. For experience-dependent changes in defensiveness response, we compared brain gene expression in control bees and bees that responded by sting extension to electric shock in a standardized individual behavioral assay. In both experiments, for neuromodulation, we examined membrane receptor genes for the biogenic amines dopamine (DopR2), octopamine (OA1), and serotonin (5HT2a), as well the gene for the enzyme responsible for serotonin synthesis (THR). For neural metabolism, we examined the expression of two Oxidative Phosphorylation Pathway “OXPHOS” genes (ND51 and ND20-LIKE). Bees collected from defensive colonies had a significantly lower expression of amine receptor, synthesis gene, and OXPHOS genes. However, bees responding to noxious stimuli (i.e., electric shock) showed greater gene expression for both OXPHOS and neuromodulation genes, except for 5HT2a. We discuss the intriguing intersection of neuromodulation and neural metabolism in defensive response both for constitutive differences, and contrasting experience dependent or adaptive differences.