Fruitless aggression

In the animal kingdom, instincts help survival. How instincts manifest themselves in the genetic and neural blueprint of each animal is largely unknown. In the latest issue of Nature Neuroscience, Vrontou and colleagues link the gene fruitless (fru) to sex-specific aggressive behaviour and the formation of dominance relationships in Drosophila melanogaster.

The fruitfly D. melanogaster has been used in the recent past as a system to study the genetic basis of aggression. D. melanogaster display a stereotyped, sex-specific aggressive fight pattern: 'lunging' and 'boxing' are characteristic for male fights, whereas 'shoving' and 'head-butting' are characteristic for female fights. Furthermore, the outcome of male fights establishes a dominance relationship and therefore will influence the outcome of subsequent fights, whereas the outcome of female fights is independent of previous encounters.

fru is a sex-specifically spliced transcription factor and has a well-established role in courtship behaviour. Vrontou et al. used flies which expressed the fru allele of the opposite sex, namely fru^M females and fru^F males. These flies were paired either with each other or with control flies in a chamber where they had to compete over food, therefore triggering aggressive behaviour.

The researchers asked two main questions: do fru splice variants influence the style of aggression, and is fru involved in the formation of dominance relationships? Their experiments showed that fru^F males fought like females in that they shoved and head-butted, rather than lunged or boxed. They also had a greatly diminished ability to form dominance relationships. fru^M females tended to court other females and normal males, and only showed aggressive behaviour when paired with fru^Fmales. In these fights the females fought by lunging and boxing, showing typical male fight behaviour; however, they did not not form dominance relationships. Therefore, switching fru reversed the sex-specific, aggressive behavioural patterns in these flies.

In conclusion, this study shows that fru genetically links aggression and courtship in D. melanogaster. Future studies will aim to identify further genes that are key components in either one or both of these opposing instincts in D. melanogaster. It will also be interesting to see if these studies can be easily translated into vertebrate and eventually human behaviour.