Honeybees communicate to their conspecifics the location of resources by performing a “waggle dance” – a complex repetition of movements consisting of a waggle and a return “run” which is unique to each particular resource location. This behavior is known to be correlated with the levels of dopamine in the bees’ heads, a “feel good” neurotransmitter that is involved in arousal, cognition, sensitivity to stimuli, and seeking and wanting behavior in many animal species.
Now, a study led by the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and the University of California, San Diego has found that receiving an inhibitory signal (stop signal) associated with negative food conditions decreased the dopamine levels in honeybees.
Although previous studies provided evidence that foragers often use the stop signal – an inhibitory signal targeted at waggle dancers – to warn other bees of a dangerous or declining food source, it was unclear how the presence of predators affected the honeybee food-wanting signal.
“We were wondering whether a signal about danger at a food source could, by itself, decrease foraging motivation and thus reduce brain dopamine levels,” said Dong Shihao, a chemical ecologist at XTBG and one of the study’s authors.
The researchers observed that, while foragers produced no stop signals when they were not attacked, when threatened by hornets, the stop signaling sharply increased, leading waggle dancers to cease their activity, abandon the dangerous feeder, and return to their hives. Moreover, the waggle dancers receiving the stop signal had significantly lower brain dopamine levels, even in cases when the dancers have not experienced peril themselves.
When the scientists increased bees’ dopamine levels by feeding them with a dopamine sucrose solution, they spent substantially more time on a feeder after being attacked by a hornet, produced fewer stop signals when returning to the hive, and performed more waggle dances than bees which were also attacked but fed pure sucrose solution.
“Attacks by hornet predators can reduce brain dopamine levels and cause foragers to pass on such stressful information via stop signals that also reduce brain dopamine levels in recipients. Artificially increasing dopamine levels by feeding bees dopamine would reduce the aversive effects of hornet attacks,” concluded corresponding author Tan Ken, an ecologist at XTBG.
The study is published in the journal Current Biology.