The key role of the brain in the evolution of feeding behavior in fruit flies

To ensure their survival in a new environment, insects must be able to change their eating habits depending on the food supply. In collaboration with experts from Switzerland, Portugal and Germany, researchers at the University of Fribourg were able to show that this ability to adapt is also controlled by mechanisms in the brain.

It is obvious: if a species cannot find its usual food in a new environment, it must adapt in order to survive. This ability to adapt to the available food supply is linked to mechanisms that have been little researched to date and which researchers from the University of Fribourg, the University of Lausanne, the Champalimaud Foundation in Lisbon and the University of Giessen have now taken a closer look at.

They studied three species of fruit flies: Drosophila melanogaster, a fly species often used in laboratories, Drosophila simulans and Drosophila sechellia. Due to their broad food spectrum with a preference for fruits with a high sugar content, the first two are considered ’opportunistic’ or polyphagous, while Drosophila sechellia, originally native to the Seychelles, feeds exclusively on noni fruits (Morinda citrifolia). The other two fly species, however, avoid these due to their bitter taste. Until now, researchers assumed that the feeding preferences of flies depended solely on the sensitivity of their peripheral sensory organs. However, with the help of genetic manipulations of all three species and modern imaging techniques, the researchers have now been able to show that the reality is much more complex.

Gourmets from head to toe

To taste their food, fruit flies use sensory cells that are distributed over their entire body, from the mouth to the wings to the feet. For this reason, it was previously assumed that the number and sensitivity of these peripheral taste sensors determined their food preferences. However, the results of a study published in the journal Nature on November 26, 2025 now highlight the role of the brain

One gene makes a (small) difference

First, the researchers conducted a series of behavioral experiments. ’In addition to sweeteners such as sucrose, we also offered the three fly species bitter substances such as caffeine as food in the laboratory,’ explains Enrico Bertolini, a researcher at the University of Freiburg. The experiments quickly showed that the feeding behavior of Drosophila sechellia cannot be explained solely by a change in their peripheral taste sensors. ’We were able to detect a slight change in a gene involved in taste perception, which is certainly partly responsible for the reduced sensitivity to bitter substances. However, this small difference alone is not sufficient to explain their almost exclusive specialization on the noni fruit,’ says Thomas Auer, assistant professor at the University of Freiburg and head of the study

Brain vs. peripheral sensors

For this reason, the researchers finally investigated how taste information is processed in the central brain of flies.

The researchers at the University of Fribourg were supported by Carlos Ribeiro and Daniel Münch from the Champalimaud Foundation in Lisbon and now at the University of Giessen. They visualized the brain activity of the flies from Thomas Auer’s laboratory using calcium imaging. ’We focused primarily on a specific part of the central nervous system below the esophagus, the so-called subesophageal region, which is important for food intake,’ Daniel Münch explains their approach

The brain sets the tone

Using this approach, the researchers were able to show that Drosophila sechellia was able to adapt its diet primarily by changing the way it processes sensory information. ’We observed that in Drosophila sechellia, the subesophageal region is more strongly activated by noni fruit than by sweet fruit juice. This stronger activation triggers movement commands for food intake. In the other two fly species, the opposite is true, which explains their preference for sweet food,’ explains Carlos Ribeiro.

In other words: In addition to the peripheral sensory organs, the brain is largely responsible for the development of insects’ food preferences.

This knowledge could be used in insect control in the future. ’So far, the focus has been on the peripheral sensory organs in order to change their feeding behavior. But this may not be the only point where we can start’, concludes Thomas Auer.

Bertolini, E., Münch, D., Pascual, J. et al. Evolution of taste processing shifts dietary preference. Nature (2025). https://doi.org/10.1038/s41586-025-09766-6