COS 97-1 - CANCELLED - Defensive shimmering responses in the giant honeybee Apis dorsata are triggered by dark stimuli moving against a bright background

Background/Question/Methods

Due to the absence of physical barriers, the open-nesting giant honey bee Apis dorsata has evolved a spectacular collective defence behaviour – known as “shimmering” – against predators. Shimmering is a highly coordinated behaviour that is generated by individual bees flipping their abdomens in a sequential manner, resulting in travelling waves across the bee curtain. Although previous studies have addressed the mechanistic aspects of shimmering response, especially from the perspective of signal propagation and information transfer, the visual features of a 'predator' or 'intruder' that lead to shimmering behaviour have not yet been elucidated. We examined the features eliciting shimmering by presenting moving grey stimuli of varying sizes and intensities against a dark or a light background in both bright and dim ambient light conditions. We explored the strength of shimmering with respect to stimuli intensity (black, light grey and dark grey), the background (black/grey) and size of the stimuli (4 cm, 8 cm, 16 cm), and quantified the interactions using beta-regression modelling. We predicted that shimmering response would correspond to the stimulus-size and the contrast of the stimulus with respect to the background. We also predicted that shimmering would be minimal or completely absent in dim ambient light conditions.

Results/Conclusions

We observed that A. dorsata shimmered only when presented with the darkest stimulus against a light background, but not when this condition was reversed (light stimuli against the dark background), even when the magnitudes of the relative contrasts were higher. The strength of shimmering also corresponded to the size of the object, and the smallest stimulus elicited no response in our experiment. Moreover, shimmering was most pronounced under bright ambient light, and its strength declined in dim-light. Our results suggest that this behaviour is an effective anti-predatory strategy in open-nesting A. dorsata colonies, which are exposed to high ambient light, as flying predators are more easily detected when they appear as dark moving objects against a bright sky. Interestingly, the stimulus detection threshold (smallest visual angular size) is much smaller in this anti-predatory context (1.6^o - 3.4^o) than in the context of foraging (5.7^o), indicating that ecological contexts affect visual detection thresholds in honey bees.