Flying (and feeding) under the radar? NOT ANYMORE
Fruit flies are sneaky – they’re too small to swat, but big enough to be a nuisance. And although it might be easy to dismiss the little creatures as simple, insignificant pests that invade your kitchen, they can actually do us a great service.
For years, scientists have used fruit flies, or Drosophila melanogaster, as test subjects because of their ability to evolve through many generations in a relatively short time. They provide an abundance of clean data, with strong control groups and a clear path for analysis. That data is valuable because the biological network of the fruit fly has many structures and dynamics similar to those of mice and humans, so researchers can unravel the complexities of a fruit fly and bypass testing larger specimens.
However, for all the biological information we have gleaned from the fruit fly, there’s one aspect of the creature that has stumped scientists for a long time.
“Monitoring the fine details of their behavior, such as how they eat, has been a challenge for many years,” said Dr. Carlos Ribeiro, principal investigator of the Behavior and Metabolism Lab at the Champalimaud Neuroscience Programme in Lisboa, Portugal. “The fruit fly is a highly valuable animal model, but they are very small.”
To monitor the fruit fly’s delicate activity, Ribeiro and his researchers developed the flyPAD (Fly Proboscis and Activity Detector), a highly sensitive device that monitors the feeding of flies through touch-screen technology.
“The technique is based on the same technology used in devices such as iPads,” Ribeiro said. “Each time the fly touches the food, we are able to detect it, allowing us to follow the details of feeding in high resolution and real time.”
The scientists discovered that fruit flies eat like humans do – with a rhythm. In humans and rodents, food ingestion is highly rhythmic with the process of tasting, chewing and swallowing. Those motor programs are controlled by central pattern generators in the brain stem. For fruit flies, their eating organ, the proboscis, extends and retracts rhythmically as well, suggesting an underlying central pattern generator. Also, after starvation, animals homeostatically compensate for a lack of energy by increasing their food intake; the same is true for fruit flies.
“When they are hungry, they do not change the rhythm of feeding,” Ribeiro said, “but instead alter how long they wait to take the next bite. This means that flies change different aspects of their behavior depending on how hungry they are. Furthermore, the way flies adapt to starvation is similar to how mammals do it.”
To determine exactly when the food reached the fruit fly’s nervous system, the scientists expressed luciferase, a fluorescent protein, into the flies’ brains. They were then fed a substance that activated the protein, and photons soon emitted from their bodies.
“This way, we could make sure that the amount and the timing of flashes from the brain are related to food intake and the kinetics of the nutrient absorption,” said Dr. Pavel Itskov, postdoctoral researcher in the Behavior and Metabolism Lab. “Not only did it confirm that the motor program we found leads to food intake, it also showed us that the food reaches the nervous system extremely fast, in as little as 20 seconds.”
Next, the scientists want to figure out how the brain regulates food intake by searching for the genes and neurons that control the fly’s feeding habits.
“Given that the regulation of this behavior seems to be similar in flies and vertebrates, there is the fascinating possibility that it is controlled by similar neuronal circuits and genes,” Ribeiro said. “This work will bring us closer to understanding how we choose what and how much to eat.”
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