Once fruit becomes putrefied, fruit flies will buzz around spontaneously. Behind this foraging behavior is an elaborate and sophisticated regulation mechanism. The research team, led by Wang Liming of the Life Sciences Institute, Zhejiang University, discovers octopamine—a molecule which mediates the foraging behavior—via the replay of the foraging behavior of fruit flies in the laboratory. Without octopamine, fruit flies won’t forage for food even if they are starving. This might be the tip of an iceberg about “eating”. The paper was published online in PNAS on April 7, 2015.
When you feel hungry, you will feel kind of edgy or rush to the canteen to grab some food. “We are most intrigued by the question concerning how animals sense hunger and what they will do afterwards,” said Wang Liming, “This process involves at least two independent steps. First, the brain detects a biological signal in the body which shows a deficiency of energy or nutrients. Second, it triggers particular emotional and behavioral responses.”
Fruit flies are one of the most favored creatures for scientists. Previous genetic studies have enabled scientists to “alter” the genes and neurons of fruit flies so as to explore the mechanism for life. Now that mankind cannot communicate with fruit flies, how can we know that they are starved? We must find a representative “starvation” behavior in them.
According to Yang Zhe, one of the first authors of the paper, foraging is used as an indicator. It has three key features: increased locomotor activity, salient targeting and strategy selection. The Fruit Flies Starvation Model satisfies all these three criteria. Interestingly enough, like human beings, fruit flies on a full stomach are relatively rational, but most ravenous fruit flies eat whatever is available.
Scientists discover a neurotransmitter—octopamine—via a series of high throughout screening. This molecule is notably similar to noradrenaline in a human body in structure. “We find that a starving fruit fly won’t forage for food sources without ocopamine. Even if its body function is complete and normal. The only difference lies in the fact that its locomotor activity won’t increase,” said Yu Yue, another first author, “Ocopamine is a key molecule in starvation-induced foraging behavior.”
“What is more interesting is that fruit flies will suffer from hunger,” said Wang Liming, “When food is fed to fruit flies, they will also open their mouth. Moreover, they have a greater appetite than those on a full stomach. In other words, if feeding is an indicator, they will still feel hungry.”
It is in the nature of living creatures that they will look for food sources when they are hungry. However, the latest research by the research team led by Wang Liming reveals wider connotations of “foraging” and “feeding”. “Popular notion has it that starvation is detected via a central nervous system, which then ignites a series of emotions and behaviors. But our research demonstrates that when the brain senses starvation, foraging and indigestion may well entail two completely independent systems, at lease in the case of fruit flies. The ocopamine deficiency blocks the foraging behavior of fruit flies, but it does not impede their food intake. They are just like two neural “pumps”. When one pump is undermined, the other is still capable of functioning properly,” said Wang Liming.
“The human brain is a very sophisticated system,” said Wang Liming, “Research into eating is, in essence, focused on how the brain detects signals in the body and make a series of responses. The findings about fruit flies can indeed facilitate the understanding of various things: the human brain, how we feel hungry, how we decide when, where and what to eat, how delectable food is irresistible to us, and how to stay healthy and keep a balanced diet.”
“Although there exists tremendous differences between tiny fruit flies and human beings, but there may well be a highly conservative regulatory mechanism in the evolutionary timeline, for how to sense starvation and how to forage for food should be the basic requirements for animals to survive and propagate,” said Wang Liming. The research team will carry out follow-up studies into the foraging behavior of fruit flies with a view to clarifying the mechanism by which the brain of fruit flies senses their metabolic level and make regulatory responses accordingly. It is expected that this research will be instrumental to our better comprehension of the human brain and ultimately our understanding of the disease-inducing mechanism for relevant metabolic diseases, such as anorexia and bulimia.