Origins of brain asymmetry: Lateralization of odour memory recall in primitive Australian stingless bees

Abstract

Left-right antennal asymmetry has been reported in honeybees. We studied primitive social bees to investigate the evolutionary origins of the asymmetry. Three species of Australian native, stingless bees ('Trigona carbonaria', 'Trigona hockingsi' and 'Austroplebeia australis') were trained to discriminate two odours, lemon (+)/vanilla (-), using the 'Proboscis Extension Reflex' (PER). Recall of the olfactory memory at 1 h after training was better when the odour was presented on the right than on the left side of the bee. In contrast, recall at 5 h after training was better when the odour was presented on the left than on the right side of the bee. An additional experiment with 'T. hockingsi' bees, fed with sugar 1 h before recall and tested at 5 h, produced similar results, showing that the shift in lateralized recall was due to the lapse of time per se and not to changes in motivation to feed. Stingless bees show the same laterality as honeybees, suggesting that asymmetry evolved prior to the evolutionary divergence of these species.