I asked the institute what absolutely MUST be included in the lecture on clock control, and they surprised me by saying time memory in honeybees. This was described first by Beling, and later was a big part of why the Munich biologist Karl von Frisch won a Nobel Prize. I'll try to explain how it works: Bees in general have a fascinating social structure and, somehow going along with that, a fascinating circadian program. Each member of the hive has a specific task and their behavioral program reflects this. If they work inside the hive, taking care of the young and keeping things clean, they show no apparent daily rhythms in behaviour. But if their job takes them outside of the hive, their activity shows daily rhythms. Then bees are generally day-active, going outside during the day and staying in the hive at night. Bees can switch between these states, -worker or forager, non-rhythmic or rhythmic behavior- but that's not the most amazing part of the story. The only task of the forager bees is to find food and bring it back for the hive and -importantly- to inform the other foragers where the good food is located. Food for bees is nectar, and flowers are usually open and full of nectar only at certain times of day. For food sources that are close at hand, communicating location is not so difficult, nor is it essential. But for those that are farther away, it would be inefficient for the bees to have to search again for an abundant food source that another bee has already identified. When a bee returns to the hive after finding a good supply of food more than about a 100 meters away, it communicates where the food is to its hive-mates. The bee does this with the wagging dance, or in German - Schwänzeltanz. Say that ten times fast! The Schwänzeltanz has a standard form, in that it looks like an 8 -two circles next to each other. When the bee crosses the middle path, as it moves to circle on the other side of the 8, it wiggles its abdomen, attracting the attention of the other bees. With the dance, the bee that has found the food source is transmitting a complex set of information to its mates. The speed of the dance shows distance, as though a tired bee, returning after a long flight, would just move slower. So tired! How is direction specified? First, it is important to know that the bees use the sun -its angle- to orient themselves in space. This is called a sun compass. Obviously, the sun moves and this requires that the animals need to have a system for marking the time at which the sun is at a certain position. This is called Zeitgedächtnis or time memory. In the Schwänzeltanz, the orientation of the figure 8 indicates the direction of the food source, with the bee essentially pointing out the food. The bees then use the angle of the sun -at that time- to find their way to their food, even on cloudy days, when they, -unlike us- can still make out the sun's direction by using polarized light. Since the sun constantly moves in relation to the food source, the bees need to integrate time, and they can only do so with the help of their circadian clock. If the food source lies to the south, they would have to leave the sun to their left in the morning, travel towards it at noon, and then leave it to the right in the evening. If one would tamper with the bees circadian clock, they would look for the angle relative to the sun but would end up in the wrong place and with no food! This is hard to imagine or to visualize. Since a picture is worth a thousand words, we made a little movie to explain it.
