Fruit fly bouts show gender-specific styles

Fighting like a girl or fighting like a boy is hardwired into fruit fly neurons, according to a study in the Nov. 19 Nature Neuroscience advance online publication by a research team from Harvard Medical School (HMS) and the Institute of Molecular Pathology in Vienna. The results confirm that a gene known as “fruitless” is a key factor underlying sexual differences in behavior. The findings mark a milestone in an unlikely new animal model for understanding the biology of aggression and how the nervous system gives rise to different behaviors.

“Aggression is a very serious problem in society, and it’s a problem with a biological and genetic component,” said co-author Edward Kravitz, the George Packer Berry Professor of Neurobiology at HMS, who developed the fruit fly fighting model used. “We want to understand that. I can’t think of a better system to study than fruit flies. And no one gets hurt.”

The fruitless gene is known for its role in male courtship. The large gene makes a set of male-specific proteins found exclusively in the nervous system of fruit flies, in about 2 percent of neurons. The proteins are necessary for normal courting. Males missing the proteins do not court females, and they sometimes court males, other research groups have shown. Females with a male version of the gene perform the male courting ritual with other females.

The same gene directs another sex-specific behavior – fighting patterns, the new study shows. Female fighting, for example, largely involves head butts and some shoving. Males prefer lunges; they rear up on their back legs and snap their forelegs down hard – sometimes nailing an opponent that is slow to retreat.

The flies undergo a major role reversal when the male and female gene versions are switched. With a feminine fruitless gene, male flies adopt more ladylike tactics, mostly the head butt and some shoving. With the masculine fruitless gene, females instinctively lunge to the exclusion of their usual maneuvers.

The gender-bending fruit flies were first developed to study courtship in the Austrian lab of co-author Barry Dickson, director of the Institute of Molecular Pathology. Dickson created male flies with the female version of the gene and female flies with the male version.