What's like rockclimbing, and listening to an allegro molto? Being a bee, according to behaviour researcher Rodrigo De Marco. I've just written a short news story for New Scientist about a study in which De Marco and colleagues used high-speed video inside a hive to glean information about the honeybee's waggle dance. When I interviewed De Marco about his research he had some lovely insights into the mind of a bee, as well as the challenges of decoding its famous dance. His comments didn't fit into the story so I thought I'd post them here as a q&a.
First some background - that honeybees use an ingenious dance to communicate the location of nearby food sources was discovered in 1946 by Karl von Frisch. Each dance consists of a series of "waggle phases" during which the bee shakes its body from side to side (see video). Von Frisch subsequently worked out that the dancer's orientation relative to gravity during each waggle phase gives the direction to the food relative to the sun's position, while the number of side-to-side movements the dancer makes gives the distance.
But in the decades since von Frisch's work, researchers have made little progress in working out other bees decode the information in the dance. Studies have shown that followers can sense vibrations and flows in the air around the dancing bee, however they also touch the dancer directly. De Marco's work, published in Animal Behaviour, is an attempt to solve that mystery...
Q: How does a honeybee move during its waggle-phase?
A: Imagine yourself rock climbing, with your hand and feet held, and moving your backpack from side to side in a controlled manner. Like that! We also know that the dancer does not keep all its feet still while wagging its body from side to side; it moves them in a systematic fashion, pretty much as you would need to move your hands and feet in order to climb up. A single waggle-phase can last from a fraction of a second to several tens of seconds, whereas an entire dance can involve from a single to hundreds of waggle-phases.
Q: You describe the question of how information from the dance is transferred to followers as a "major gap" in understanding. Why has it been so difficult to work this out?
A: To start with, there is a grave lack of understanding of the sensory horizon of honeybees. What is meaningful input for a honeybee? How are different meaningful inputs combined? Answering this question also involves solving several separate puzzles. For example, what is the nature of the uncertainty that the dancers' audience experiences prior to and during dance following? What are the relevant cues and signals associated with the dance? How are such cues and signals being integrated from the sender's and the receiver's side of the communication process? To make matters worse, it is difficult to observe the behaviour of both dancers and followers simultaneously, and even more difficult to observe them both inside and outside the hive. So it is very hard to track the ultimate effect that the dance has on the behaviour of the individual followers.
Q: You used high-speed video to record more than 40 dances, with nearly 400 followers. What did you find?
A: We found that the higher the number of the dancer's wagging movements, the higher the number of the followers' antennal deflections.
Q: So in a sense the followers use their antennae to "count" the number of wagging movements?
A: Using the word counting would imply that followers can compute deflections of a certain size as discrete events, but we do not know whether this is how the deflections are processed by the brain. I think that instead the bees may be sensing the length of time over which the stimulation occurs, as a person might estimate the duration of a piece of music. Imagine the difference between listening to either a short or a long allegro molto.
Q: How do the followers estimate the orientation of the dancer with respect to gravity?
A: We found that the type of stimulation the followers receive depends on their position relative to the dancer. For followers who face the dancer from the side, contacts are more obvious and regular, and involve both antennae, whereas from behind they are more subtle, a bit less regular, and involve one antenna at a time. The followers might be able to use this information, combined with knowledge of their own position, to figure out the dancer's orientation. Imagine a situation in which you can easily orient your body either vertically or horizontally, and that when you find the right orientation, this is signalled to you by the occurrence of music, or a certain kind of motion. You would only need to figure out what the orientation of your body is when the music (or motion) occurs to find out what the relevant orientation is.
Q: Are the antennal deflections sufficient to transmit all the information that the followers need, or are they using other information sources too?
A: It would be unwise to imagine that honeybees rely on a single pathway. I think that we would learn a great deal by looking at how honeybees interact with each outside the hive. Can they follow each other? If yes, to what extent? The dance may be great advertisement, but it might well be that more is needed to bring the audience to the actual target.
Q: Why do you find these dances so fascinating?
A: Because their occurrence and shape can be predicted by a human observer. Hence, they are useful to gather insights about how information flows in nature. There are other communication systems in nature that humans can interpret, but in most cases the function they serve isn't so obvious. With the dance, the ultimate goal is simply to recruit comrades. Bees also have quite a restricted repertoire of behaviours. So we can observe the behaviour of dancers and followers and make very clear predictions about what we expect to see. That gives us a good chance of finding ‘meaningful' correlations. A panacea for ethologists! However, there is a danger here too: the study of the honeybee dance has frequently led to oversimplified interpretations about communication and behaviour. It seems that, sooner or later, students of the honeybee dance tend to find themselves embracing their own hypotheses a bit too kindly, instead of fighting them properly. I still fail to understand why - could it be that the idea that honeybees ‘read' the dance as we do becomes at some point irresistible?
PS De Marco carried out this research at the Freie Universität Berlin, however he is now at Max Planck Institute for Medical Research in Heidelberg, studying behaviour development and the development of neuronal circuits underlying the so-called stress response.
PPS OK so this doesn't have anything to do with the Antikythera mechanism. But De Marco's paper does have "decoding" in the title :-)