Even maggots strive for profit

Behavioral experiments reveal unexpected capabilities in invertebrates

Head of a chrysalis larva in the scanning electron microscope: The mouth is surrounded by barbels, above which are the wart-like taste and smell organs of the animal. © Kirsa Neuser, Georg Krohne
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In the summer it can happen quickly: The bio-bin fills with unwelcome guests. Often, there are hosts of insatiable maggots, the lavish on the kitchen waste. Forbidden, brainless creep? Absolutely not. Also, maggots with their simple nervous system are capable of amazing behavioral performance. Researchers at the Biocenter of the University of Würzburg have now shown that the animals in some way even "think" about the consequences of their behavior.

The three-millimeter-sized maggots of the fruit fly Drosophila can learn through experience that one particular odor promises sugary food, while another scent does not. They keep that in mind. "If you smell the former scent again later, you will remember that it signals the presence of sweet food, " says biologist Bertram Gerber. But: before the larvae run straight to the source of the odor, they "think".

First of all, they check which situation they are in at the moment and whether in this situation it really has the advantage of moving towards the scent. If the larvae are already sitting on a pile of sweet food anyway, they will not take a step towards the smell of sugar. But if they do not have any food at the moment, they will make their way to the better laid table.

Evaluation of the situation also in lower animals

"The larvae convert the information from their memory into behavior only if that brings them something, they are striving for profit, so to speak", Gerber sums it up. The fact that there is still a regulatory intermediate step between retrieving the memory and the resulting action - in this case an assessment of the situation, so to speak a "reflection" - has hitherto only been known by humans and higher animals, but not by insects. The Würzburg researchers conclude that the "contemplation step"

generally fundamental for the behavioral control is - an assumption, which is represented in particular by the Würzburg psychology professor Joachim Hoffmann. display

Learning through experience

The experiments that Gerber and his colleague Thomas Hendel made on the suggestion of Hoffmann are described in detail in the journal Proceedings of the British Royal Society. Incidentally, they also worked in the other direction: In this case, the fragrances that the larvae had noticed during training signaled not good, but disgusting food - the scientists had treated it with extremely high levels of salt or bitter substances.

Again, the animals had a choice: from one direction they were served a neutral scent, from the other they were enveloped by the smell, which reminded them of salty food. In a neutral situation they made no move to change their place. However, when the same experiment was done on over-salted food, the larvae moved towards the neutral odor. Through this behavior, they escaped the unpleasant situation. In the first experiment, however, it would not have given them any advantage to leave their place.

(University of Würzburg, 14.09.2006 - NPO)