The aggressive behaviors male flies display towards other males, particularly in the presence of female mating partners, can be reduced if the males are previously exposed to female flies. The results, published online this week in Nature Neuroscience, further show that this suppression of aggression towards sexual competitors is mediated by a female pheromone detected by a specific neural circuit present only in male flies.
Prior social experiences are known to influence various behavioral interactions amongst the fruit fly Drosophila melanogaster. Aggressive behavior towards other members of the same species is seen across the evolutionary spectrum, and male flies are known to exhibit various aggressive postures and gestures including a male fly lunging towards another.
Yuh Nung Jan and colleagues found that male flies show less aggressive behavior towards other males if the aggressor male was previously housed together with female flies for several days. This inhibition of aggression only occurred following prolonged exposure to the females of the same Drosophila species, and required physical contact between male and female flies. Neither exposure to just visual or olfactory cues of the opposite sex, nor brief episode of copulation itself was sufficient to blunt the aggressive behaviors. Jan and colleagues also examined the specific neural circuit that mediates this inhibition of aggression. They found that pheromones released by female flies are detected by male chemical receptors on the bristles of their legs. This chemical information is then conveyed to a neural circuit unique to the male fly’s brain.
Male-male aggression can influence mate competition and bias reproductive advantage, and this behavior is highly conserved across different species of animals. The current work provides insights into how this behavior can be modulated by prior social experience.