Dueling fruit flies
Apparently male fruit flies fight. Who knew? According to biologist David Anderson from the fly laboratory of California Institute of Technology (Caltech), Drosophilae, commonly known as fruit flies, fight regularly. Males in particular put up a big fight in the presence of a female because males have special cells in their brains that promote fighting that are absent in the brains of female fruit flies.
"The sex-specific cells that we identified exert their effects on fighting by releasing a particular type of neuropeptide, or hormone, that has also been implicated in aggression in mammals including mouse and rat," says Anderson, author of the study. "In addition, there are some recent papers implicating increased levels of this hormone in people with personality disorders that lead to higher levels of aggression."
Genetically the fruit fly's genes are quite similar and play similar roles, to those of a human being. But while their basic cellular functions and development are similar, researchers are not sure whether these genes control complex social behaviors like aggression.
"Our studies are the first, to our knowledge, to identify a gene that plays a conserved role in aggression all the way from flies to humans," explains Anderson. If that is true for one such gene, it is also is likely true for others, Anderson says. "Our study validates using fruit flies as a model to discover new genes that may also control aggression in humans."
Fruit flies have a less complex nervous system than humans making them easier to study. The research team created a small library consisting of 40 different fly lines. A different set of specific neurons in each fly line was genetically labeled and could then be artificially activated. Each neuron type secreted a different neuropeptide and was tested upon activation for its ability to increase aggression. The neuron exhibiting most dramatic increase in aggression had neurons expressing a particular neuropeptide called tachykinin, or Tk.
Anderson and his colleagues then used a set of genetic tools to identify exactly which neurons were responsible for the effect on aggression and to determine if the encoding gene for Tk also controls aggressive behavior by acting in that cell.
"We had to winnow away the different cells to find exactly which ones were involved in aggression—that's how we discovered that within this line, there was a male-specific set of neurons that was responsible for increased aggressive behavior," explains Kenta Asahina, postdoctoral scholar in Anderson's lab.
Read more at Caltech.