Alcohol in their food increases the production of sex pheromones in male fruit flies, making them more attractive to females
A team of researchers at the Max Planck Institute for Chemical Ecology has investigated why the fruit fly Drosophila melanogaster drinks alcohol and has shown that alcohol has a direct and positive effect on the mating success of male flies. This effect is due to the increased production of sex pheromones after alcohol consumption, which makes males that have consumed alcohol more attractive to females. Male flies are therefore strongly attracted to alcohol, especially when they are not yet mated. Three different neural circuits in the flies' brains control the response when the flies smell alcohol: While two olfactory receptors are responsible for attracting male flies to small amounts of alcohol, a third ensures that excessive amounts have a deterrent effect. Because alcohol is toxic, the flies must carefully weigh the risks and benefits of drinking alcohol.
Alcohol makes male fruit flies of the species Drosophila melanogaster more sexy by stimulating the production of sex pheromones. As a result, male flies are more successful at mating after consuming certain amounts of alcohol.
© Anna Schroll
To the point
- Reason for drinking alcohol: Alcohol has a direct and positive effect on the mating success of male flies.
- Attractive to females: This effect is due to the increased production of sex pheromones after alcohol consumption, which makes males that have consumed alcohol more attractive to females. Male flies are therefore strongly attracted to alcohol, especially when they are not yet mated.
- Neural circuits in the flies' brains: While two olfactory receptors are responsible for attracting male flies to small amounts of alcohol, a third ensures that excessive amounts have a deterrent effect. Because alcohol is toxic, the flies must carefully weigh the risks and benefits of drinking alcohol.
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.
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 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 different neural circuits
"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.
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.
