The work is reported by Jean-Francois Ferveur and colleagues at the Universite de Bourgogne, France, and the University of Manchester, United Kingdom.
When an adult male fruit fly encounters a young male fly, he will actively court the younger individual, sometimes becoming aggressive. These young males that have encountered older flies will go on to similarly dominate other adult males that had encountered only young flies--something in the early experience of the "dominant" flies makes them more aggressive. In the new work, researchers investigated exactly what it is about past experience of these flies that influences adult behavior. Clues caused the researchers to suspect that a key role was played by a chemical signal--a pheromone--carried by adult males during the early encounter.
To prove this, the researches used mutant flies that lack the normal adult pheromones, and they covered these pheromone-defective flies with a variety of other smells. The researchers were able to demonstrate that a male shows courtship dominance behavior over young males if he has been exposed to the smell of normal adult males during a critical period in his life--the first 24 hours. In fact, an encounter with a single adult male was sufficient to make males exhibit dominance behavior when they reached adulthood. The researchers found that, intriguingly, it was not enough for young males to smell these pheromones--the pheromones had to be carried by active adult males. The effect was so strong that males carried on exhibiting courtship dominance be havior until they were five days old.
The authors of the study note that similar findings have been reported in mice and hamsters, suggesting that dominance behavior may often be affected by chemical signals. In future studies, the researchers hope to take the next step in understanding how dominance behavior develops and thereby to identify which parts of the fly's brain are involved in processing dominance-inducing signals.