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.

Fruit
fly image via Daily Tech and apple
image via Shutterstock. Images merged and morphed by Robin Blackstone.