Bee learning and communication
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Bees learn and communicate in order to find food sources and for other means.
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Learning
Learning is essential for efficient foraging. Bees are unlikely to make many repeat visits if a plant provides little in the way of reward. A single bee will visit different flowers in the morning and, if there is sufficient attraction and reward in a particular kind of flower, she will make visits to that type of flower for most of the day, unless the plants stop producing reward or weather conditions change. Bees are quite adept at associative learning, and many of the standard phenomena of conditioning take the same form in bees as they do in the vertebrates that are the more usual subjects of such experiments.
At least one recent study indicates that bees can perform learning tasks that go beyond simple conditioning. Martin Giurfa of the Centre of Animal Cognition Research in France, along with four co-authors, published The concept of 'sameness' and 'difference' in an insect (http://www.nature.com/nature/journal/v410/n6831/abs/410930a0_fs.html) in the April 19, 2001 issue of Nature. In Giurfa's experiment, bees were trained to enter a simple Y-shaped maze that had been marked at the entrance with a particular color. Inside the maze was a branching point where the bee was required to choose between two paths. One path, which led to the food reward, was marked with the same color that had been used at the entrance to the maze, while the other was marked with a different color. Bees learned to choose the correct path, and continued to do so when a different kind of marker (black and white stripes oriented in various directions) was substituted for the colored markers. When the experimental conditions were reversed, rewarding bees for choosing the inner passage marked with a symbol that was different than the entrance symbol, the bees again learned to choose the correct path. "Thus," write Giurfa et al., "not only can bees learn specific objects and their physical parameters, but they can also master abstract inter-relationships, such as sameness and difference."
Communication
Bees communicate their floral findings in order to recruit other worker bees of the hive to forage in the same area. The factors that determine recruiting success are not completely known but probably include evaluations of the quality of nectar and/or pollen brought in.
There are two main hypotheses to explain how foragers recruit other workers — the "waggle dance" or "dance language" theory and the "odor plume" theory. The dance language theory is far more widely accepted.
Dance language
It has long been known that honeybees perform a dance on their return to the hive, known as bee dance or waggle dance. The nectar-laden bee dances on the comb in a circular pattern, occasionally crossing the circle in a zig-zag or waggle pattern. Aristotle in 330 BC, described this behaviour in his Historia Animalium (http://etext.lib.virginia.edu/toc/modeng/public/AriHian.html). It was thought to attract the attention of other bees.
In 1947, Karl von Frisch correlated the runs and turns of the dance to the distance and direction of the food source from the hive. The orientation of the dance correlates to the relative position of the sun. There is no evidence that this form of communication depends on individual learning.
Von Frisch performed a series of experiments to validate his theory. He was awarded the Nobel Prize in Physiology or Medicine in 1973 for his discoveries.
Odor plume
While the majority of researchers believe that bee dances give enough information to locate pollen, proponents of the odor plume theory argue that the dance alone is insufficient to give other bees guidance to the nectar source. They argue that bees instead are primarily recruited by odor. The purpose of the dance is to attract attention to the returning worker bee so she can share the odor of the nectar with other workers who will then follow the odor trail to the source.
The primary lines of evidence used by the odor plume advocates are 1) clinical experiments with odorless sugar sources which show that worker bees are unable to recruit to those sources and 2) logical difficulties of a small-scale dance (a few centimeters across) giving directions precise enough to hold the other bees on course during a flight that could be several kilometers long. Misreading by even a few degrees would lead the bee off course by hundreds of meters at the far end.
Critics of the odor plume theory counter that most natural nectar sources are relatively large - orchards or entire fields. Precision may not be necessary or even desirable. They have also challenged the reproducibility of the odorless source experiment.
The academic debate between these two theories is extremely polarized and often hostile. Note: Essentially all the research on the two competing hypotheses of communication has been restricted to honeybees. Other bees may use other methods altogether.
Adrian Wenner, a modern bee researcher, is the chief proponent of the odor plume theory (anti-dance).
Trophallaxis
The exchange of food, trophallaxis, is also used by means to communicate and includes information on the quality of and thus competition for a food source, temperature and water demand, and the condition of the queen (Sebeok, 1990).
Primer Pheromone (honey bee)
Research that was published in November 2004, by scientists under the leadership of Dr. Zachary Huang, Michigan State University indicates that so called primer pheromones play an important part in how a bee colony adjusts its distribution of labor most beneficially. In order to survive as a bee colony of sometimes 50,000 -100,000 individual bees, the communal structure has to be adaptable to seasonal changes and the availability of food. The division of labor has to adjust itself to the resources available from foraging. While the division of labor in a bee colony is quite more complex, the work can be roughly seen as work inside the hive and outside the hive. Younger bees play a role inside the hive while older bees play a role outside the hive mostly as foragers. Huang's team found that forager bees gather and carry a chemical called ethyl oleate in the stomach. The forager bees feed this primer pheromone to the worker bees, and the chemical keeps them in a nurse bee state. The pheromone prevents the nurse bees from maturing too early to become forager bees. As forager bees die off less of the ethyl oleate is available and nurse bees more quickly mature to become foragers. It appears that this control system is an example of decentralized decision making in the bee colony.
External links
- Honeybee Communication (http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/BeeDances.html)
- Genetic Control of the Honey Bee(apis mellifera) Dance Language: Segregating Dance Forms in a Backcrossed Colony (http://www.bio.usyd.edu.au/Social_InsectsLab/BensPDFs/Johnson&2002JHered.pdf)
a very detailed introduction to the honey bee dance language. It's a .pdf file. - Paper by Adrian Wenner: http://www.beesource.com/pov/wenner/jib2002.htm
- Martin Giurfa, et al.: The concepts of 'sameness' and 'difference' in an insect (http://www.nature.com/nature/journal/v410/n6831/abs/410930a0_fs.html), Nature, 410, 930-933 (19 April 2001)
Source
- Sebeok (1990). Essays in Zoosemiotics. Toronto: Toronto Semiotic Circle. ISSN 08385858.
- Huang (2004) Regulation of Behavioral Maturation in Honey Bees by a New Primer Pheromone, Proceedings of the National Academy of Science Biological Sciences, Population Biology