Alcohol makes male flies sexy

(Press-News.org) The fruit fly Drosophila melanogaster is also known as the pomace or vinegar fly. It can be found in large numbers in organic waste bins during the summer and in the fruit and vegetables section of grocery stores on hot days. It is attracted to the odor of pre-rotting fruit, where microorganisms, especially yeasts, have multiplied and invaded the fruit and switched their metabolism to alcoholic fermentation. This is why rotten fruit contains significant amounts of alcohol.

Alcohol consumption requires a risk assessment

There is no doubt that the consumption of large amounts of alcohol is harmful to human beings.. How alcohol affects insects, such as the vinegar fly, however, has been more controversial. A team of researchers from the Departments of Evolutionary Neuroethology and Insect Symbiosis and the Olfactory Coding Research Group at the Max Planck Institute for Chemical Ecology set out to investigate the effects of alcohol on flies. "In our experiments, we show a direct and positive effect of alcohol consumption on the mating success of male flies. The effect is caused by the fact that alcohol, especially methanol, increases the production of sex pheromones. This in turn makes alcoholic males more attractive to females and ensures a higher mating success rate, whereas the success of drunken male humans with females is likely to be questionable," summarizes first author Ian Keesey.

According to the study, unpaired males in particular are attracted to alcohol. Alcohol attraction, however, is controlled by how they detect and process the smell of alcohol in their brains. It is important for the flies to correctly weigh whether the odor concentration is still attractive or already repulsive in order to avoid alcohol intoxication.

Alcohol attraction and repulsion mediated by three different neural circuits to avoid intoxication

"What is unique about our results is that we found not just one, but three neural circuits that we were able to show actually balance each other in terms of this risk assessment, that is, attraction and aversion. This means that the flies have a control mechanism that allows them to get all the benefits of alcohol consumption without risking alcohol intoxication," Keesey explains. Neurophysiological studies had shown that the attraction of alcohol in vinegar flies is based on two sensory input lines for ethanol and methanol. At the same time, in the case of excessive and toxic concentrations, especially for methanol, a third line evokes repulsion. "That different neural pathways with opposite valence for the same odor are combined to balance attraction and aversion based on physiological state is a rarity," says Keesey, who conducted the research at the Max Planck Institute and is now an assistant professor at the University of Nebraska at Lincoln.

Ecological relevance

For their investigations, the researchers combined physiological studies, such as imaging techniques to visualize processes in the fly brain, chemical analyses of ecologically relevant environmental odors, and behavioral studies to observe and measure the attractiveness of odors and mating success. "The study provides one of the first comprehensive explanations of alcohol attraction in a model organism, from chemistry to ecology and from brain to behavior and vice versa. It also shows how important it is to consider the natural behavior and ecology of animal models when using them to study physiological and behavioral processes," summarizes Bill Hansson, head of the Department of Evolutionary Neuroethology at the Max Planck Institute.

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