Variation in behavioural maturation in tropical honey bees corresponds with hormonal and molecular differences

Division of labour in honey bees is based on a process of behavioural development in which the worker bee successively performs different tasks at different ages. Workers start with tasks within the nest and move on to become foragers. In Apis mellifera, juvenile hormone and vitellogenin are major drivers of this behavioural maturation, which is accompanied by changes in brain physiology, including changes in neuronal gene expression and synaptic connections. Based on this detailed knowledge, we asked whether and how major characteristics of the behavioural maturation process vary among two tropical Asian honey bee species, the phylogenetically ancestral open-nesting Apis florea and the cavity-nesting Apis cerana, a sister species to Apis mellifera. Our behavioural studies showed that workers of A. florea exhibited a slower pace of behavioural maturation than A. cerana, with greater individual variation in the age at onset of foraging. In both species, the expression pattern of juvenile hormone and foraging-associated transcription factors broadly mirrored those reported for A. mellifera. In contrast, expression dynamics of vitellogenin and nurse-associated transcription factors in both species did not show the clear age- or task-related pattern as reported for A. mellifera. Notably, workers of A. florea consistently exhibited substantially higher vitellogenin expression levels than did A. cerana workers. Based on our findings, we propose that evolution of accelerated behavioural maturation in cavity-nesting species is primarily attributed to changes in the temporal dynamics of juvenile hormone signalling, whereas vitellogenin levels might vary according to different social functions.