The waggle dance is an elaborate mode of communication used by honey bees to signal to hivemates the location of food and potential new nesting sites. The dance takes the form of a figure of eight, and is performed by worker bees on the vertical surface of a comb near the entrance to the hive. As the worker moves along the straight line in the figure of eight, it waggles from side to side. When this “waggle phase” is complete, the bee performs the return phase of the dance, during which it circles to one side and returns to the starting point. This sequence is then repeated over and over again, with the direction of the return phase circling alternating each time.
The worker may perform this dance more than 100 times. The duration of the waggle phase is correlated to the distance of the food source, and the number of cycles performed to the size of the food supply, so that the further the foraging site, the longer the duration of the waggle, and the bigger the food source the greater the number of dance cycles. The angle of the straight line from the vertical is equal to the angle between the food source and the sun upon departure from the hive, and the vigor with which the waggle is performed is an indication of how much food is present at the site.
The waggle dance of the honey bee was ingeniously discovered by Karl von Frisch, the father of ethology, in the 1930s. von Frisch noticed that once a bee has found a feeding station, it is soon joined by many other bees at the same location. He was sure that the workers used visual communication to recruit other bees to the foraging site, and observed very closely the behaviour of the workers at the hive. Once he thought that he had elucidated the language of waggle dance, he built a mechanical bee to test his theory. He determined that his “translation” of the waggle dance was correct by placing the robot bee in a hive, and giving workers false directions to non-existent food sources. von Frisch also discovered that honey bees have colour vision, and was awarded a Nobel Prize for his work on animal behaviour.
The recent completion of the honey bee genome led to the identification of a number of neuromodulators which may be involved in the social behaviour of the honey bee. However, the genetic basis of the social behaviour of bees, and other social insects, is still a mystery, and the neural basis of the honey bee waggle dance is unknown. Now, a team of Australian and American researchers show that the dance behaviour is modulated by octopamine, a neurotransmitter which is closely related to noradrenaline.
Evidence that octopamine is involved in the waggle dance comes from previous studies in which more waggle dancing was observed in colonies fed the octopamine precursor dihydroxyphenylalinine. Octopamine, which is also present in the vertebrate brain, is thought to be involved in the division of labour that takes place in bee colonies, as previous work has shown that oral treatment with the transmitter accelerates the rate at which immature bees turn into foraging workers. The transmitter is also known to be present in higher concentrations in worker bees’ brains than in the brains of other bees in the colony.
The authors of the current study housed experimental honey bee colonies in glass-walled observation hives, gave worker bees food containing octopamine, and then filmed the waggle dances they performed. It was found that workers treated with the transmitter were more likely than untreated bees to perform the waggle dance upon their return to the hive, and also danced for longer than they should. Frame-by-frame analyses of the films revealed that both the intensity and duration of the dance were highly sensitive to octopamine. This effect was dose-dependent – low doses of octopamine increased the number of waggle phases performed in a dance while decreasing the duration of the return phase, but higher doses led only to an increase in the number of dance cycles. As a result, the bees consistently overestimated the size of the food source being advertised to the rest of the colony. The effects of octopamine on dance behaviour were blocked by the octopamine antagonist mainserin, suggesting that the effect of the transmitter on the dance is mediated by octopamine receptors.
The authors propose that octopamine modulates general reward responses in the honey bee brain, and suggest that octopaminergic transmitter systems in the bee’s brain may be analogous to the reward circuits in the mammalian brain which use the transmitter dopamine. The waggle dance is an example of altruistic behaviour, because it is the colony as a whole, rather than the individual dancing worker, which benefits from the performance of the dance. The altruism of the workers is essential for the survival of the colony, and the rewarding effect of performing the waggle dance, mediated by octopamine, may therefore have been crucial in the evolution of this altruism.
- Barron, A. B. et al. (2007). Octopamine modulates honey bee dance behavior. PNAS DOI: 10.1073/pnas.0610506104.