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A Bee Sees (Symmetry)


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Many researchers have assumed that only animals with relatively complex brains--such as dolphins, apes, and birds--can distinguish between symmetrical and asymmetrical patterns. But a team of German researchers has found that honeybees, which have brains consisting of just several hundred thousand neurons, are symmetrically minded also.

The researchers, led by neurobiologist Martin Giurfa of the Free University of Berlin, first trained the honeybees to forage in a garden at eight feeding stations mounted on a wall near their hive. At each station were three feeding tubes, and on each tube was mounted a black-and-white pattern. The patterns consisted of various solid shapes and line drawings. For half the bees trained, two of the three patterns were always bilaterally symmetrical--that is, the left side was a mirror image of the right. The third pattern was asymmetrical. For the other group of bees, the situation was reversed: two patterns were asymmetrical, the third symmetrical. In both cases the bees were rewarded with sugar water when they chose the odd pattern.

Giurfa and his colleagues then changed the patterns and retested the bees, this time without a food reward. The bees, of course, looked for their reward anyway. The asymmetrically trained bees chose asymmetrical patterns 75 percent of the time. The other group correctly chose symmetrical patterns in nine out of ten cases.

Studies have shown that nectar-rich flowers are often highly symmetrical, and bees, Giurfa suspects, have probably evolved the ability to recognize this feature. How the bees, with their seemingly simple brains, pull this off is another question.

I tend to think that this is not some incredible cognitive performance, Giurfa says, but that there is some element in the visual area of the bee brain--say, a neuron that fires when the bee sees something symmetrical, and a neuron capable of firing when it sees something asymmetrical. We don’t have evidence for this, but bees and insects do have receptors for special features, like edges and the orientation of lines, so why not some element that fires for symmetry?

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