Aggressive behavior has been extensively studied, both in vertebrate and nonvertebrate model organisms. Remarkably, these studies indicate common elements that underlie socially mediated changes in behavior. For example, chemical messengers such as serotonin have been implicated in aggression in mammals and crabs. It is rather surprising then, that the fruit fly, Drosophila, has not been used to explore the molecular genetics of aggression, despite the fact that this type of behavior has been documented in flies. We have been attempting to find out which genes and proteins get “turned on” in flies when they behave aggressively to each other.
We can then take these candidate aggressive genes and, using various techniques, express them at high levels in a fly to see if it becomes more aggressive.
As most of the aggressive interactions in fruit flies occur during defense of a resource such as food, territory, or a mate, we have studied male-male aggressive encounters on a patch of food. We have found that fruit fly males can be extremely aggressive with each other, or, at the other extreme, barely notice each other at all. As these flies are genetically identical, we can ask the question, “which genes have been turned on in the very aggressive flies, compared to those that are more ‘mellow’ and nonaggressive?.” To answer this question, we have made use of a relatively new technology called microarray analysis, which allows us to study the expression of all of the fly’s thirteen thousand genes at once. Thus we take very aggressive and very “mellow” flies, mash up their heads, extract the working copy of every one of their genes, the RNA, and, using the microarray, measure which genes show relatively high or low levels of RNA in the two types of animals. In this way we obtain a gene profile of the aggressive and the nonaggressive flies. We can then take these candidate aggressive genes and, using various techniques, express them at high levels in a fly to see if it becomes more aggressive. We can even modify this procedure and overexpress these candidate “aggro” genes in specific regions of the brain, thereby mapping brain structures with behavior. Because it appears that vertebrates and insects may share many of the genetic elements for aggression, our findings with the fruit fly model shall be of fundamental interest to those working on human aggression.