Courting the Competition: Some Male Fruit Flies Serenade Each Other Rather Than Fight

Like the males of many animal species, male Drosophila melanogaster fruit flies, a commonly studied lab animal, are aggressive toward one another and even fight when competing for resources such as food and females. Researchers in the lab of David Anderson have been studying aggression in these insects for decades, elucidating the neural basis for heightened aggression in males, among other discoveries.

More recently, Anderson's lab turned its attention to other species of fruit flies to see if these behaviors persist across the genus. Generally, they do—except in the African fruit fly D. santomea. These insects have evolved another tactic: courtship.

"All the conditions we've used to study aggression in other fruit fly species were the same, so we were expecting fighting, but these males behaved sexually toward one another," says Youcef (Joe) Ouadah, a senior postdoctoral scholar research associate in biology and biological engineering in the Anderson lab. "They courted one another all the livelong day, even though they were set up in the lab by us to fight."

In a new study, Ouadah, Anderson, and their colleagues examined the underlying biological mechanisms for such male same-sex sexual behavior (SSB) in D. santomea and traced it to evolutionary changes in pheromonal signaling pathways in both males and females. Although male-male courtship behavior in other insects is often attributed to an inability of males to distinguish other males from females, that does not appear to be the case in this instance.

"It's important to note that despite observing strong male–male courtship behaviors, the D. santomea males can distinguish males from females and reproduce at typical rates," says Ouadah, lead author of the paper. "Things still work out for mating, but the males don't have to fight each other."

The findings are described in a paper published online March 20 in the journal Current Biology.

Read more on the Caltech website.