To survive in a new environment, animals have to be capable of adjusting their food preferences to the food available. By studying fruit flies, scientists at the University of Fribourg working in collaboration with Swiss, Portuguese and German colleagues have demonstrated that this faculty of adaptation depends on mechanisms in the brain.

To put it simply: a species runs the great risk of going extinct if it is incapable of developing a taste for local food when displaced to a new environment. The capacity to adapt one’s dietary regime depends on mechanisms about which little is known; scientists from four institutions — the University of Fribourg, the University of Lausanne, the Champalimaud Foundation in Lisbon and the University of Giessen in Germany — sought to find out more.

To do so, they studied three species of fruit fly: Drosophila melanogaster, a fly often used in laboratory experiments, Drosophila simulans and Drosophila sechellia. Where food is concerned, the first two are regarded as “opportunists” or polyphagous, as they feed on a wide variety of foods, especially fruits rich in sugar. The third, however, Drosophila sechellia, is native to the Seychelles and feeds exclusively on noni (Morinda citrifolia), a particularly bitter fruit that the two other fruit flies carefully avoid. Until now, scientists thought that the flies’ food preferences were determined solely by the sensitivity of their peripheral sensory receptors. Thanks to genetic manipulations in all three species combined with the very latest imaging technology, these researchers have now proved that the answer is more complex.

Gourmets from head to leg
To taste their food, fruit flies use sensory neurons located all over their body, from the mouth to the wings right down to their legs. Logically, scientists assumed that food preferences were determined first and foremost by the number and sensitivity of these peripheral taste neurons and their receptors. But this study, published on 26 November 2025 in the journal Nature, shows that the brain also has a say.

A gene that makes a (tiny) difference
First of all, the scientists subjected the three fly species to a series of behavioural experiments. “In the laboratory we presented them with bitter substances — especially caffeine — and sweet substances such as sucrose,” says Enrico Bertolini, a researcher at the University of Fribourg. These tests rapidly showed that the eating behaviour of Drosophila sechellia could not be explained solely by changes in its peripheral taste receptors. “We discovered that a gene involved in taste perception had undergone a slight modification, making the insect less sensitive to bitterness than its two cousins, but this minute evolution alone could not explain its exclusive preference for noni,” explains Thomas Auer, Assistant Professor in Fribourg and lead author of the study.

Brain versus peripheral receptors

The scientists then decided to take a closer look at how the flies process taste data in their central brain. This led the researchers at the University of Fribourg to seek out the expertise of Carlos Ribeiro and Daniel Münch, researchers at the Champalimaud Foundation in Lisbon and now University of Giessen. Using calcium imaging, they succeeded in visualising the brain activity of flies supplied by Thomas Auer’s laboratory. “We focused more specifically on a region of the central nervous system called the suboesophageal zone, which is crucial to feeding,” explains Daniel Münch.

The brain gives the orders
This approach enabled the researchers to demonstrate that Drosophila sechellia was able to adapt its diet by changing the way it processed sensory data. “In concrete terms, we observed that in Drosophila sechellia, the suboesophageal zone is activated more strongly when we offer noni rather than sweet juice. This stronger activation then triggers the motor commands linked to feeding,” Carlos Ribeiro explains, “and the opposite is true for the two other flies, which explains their preference for sweet foods.”
In other words, changes in the insects’ food preferences need to be investigated in the brain and not solely at the level of the peripheral sensory neurons.
This discovery could have applications in insect-control strategies. “Until now, we thought we had to act on their peripheral receptors to modify their food preferences. Perhaps that’s not the only solution,” concludes Thomas Auer.

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