Fighting Flies: The Neurobiology of Drosophila Aggression
Aggression and aggressiveness are the biological basis of violence in human society. There are many possible ways to define violence. The World Health Organization defines
violence as"The intentional use of physical force or power, threatened or actual, against oneself, another person, or against a group or community, that either results in or has a high likelihood of resulting in injury, death, psychological harm, maldevelopment or deprivation." As such, the impact of violence can be seen, in
various forms, in all parts of the world. Each year, more than a million people lose their lives, and many more suffer non-fatal injuries, as a result of self-inflicted, interpersonal or collective violence. Overall, in the early years of the 21st century, violence is among the leading causes of death worldwide for people aged 15–44 years.
Therefore, the basic neurobiological science of research into the mechanisms for aggressiveness and aggression in the brain has not only basic, but also a tremendous societal value. Aggressive acts occur when resources or rights are challenged. In evolution, aggression often evolved into highly ritualized behaviors, with minimized bodily harm as a consequence. Studying the neurobiological underpinnings of aggression in many different animal model systems and understanding the life-history strategies of these animals (in which their aggressive behavior is embedded) will therefore provide unique and thought provoking insights for aggression research in humans. Eventually, such research will aid in reducing the cost of human aggression. One very little understood model system for the study of the neurobiology of aggression is the fruitfly Drosophila.
Ever since T. H. Morgan brought Drosophila into the laboratory, the little fruitfly has served as the "Jack of all trades" model system for a wide variety of biological fields: Genetics, Biomechanics, Developmental Biology, Evolutionary Biology, Pharmacology, Neurogenetics, Ecology and many more. In one particular field, the fly is hardly studied at all: the neurobiology of aggression. It has been known for many years that a variety of Drosophila species fight for resources. The circumstances under which Drosophila exhibits territoriality and aggression are well studied.
The neurobiological techniques are at hand to interfere with the neural substrate of aggression at various levels. What was needed was a coarse tool to screen for candidate variables that influence aggression and a quantitative framework for the fine dissection of neurobiological effects on the agonistic behaviors. Following the initiative of Harvard Professor Edward Kravitz, two students and I designed an experiment to test a number of possible neurobiological determinants of aggression, while the Harvard people developed the quantitative behavioral framework. Both studies appeared almost simultaneously. Our paper was published by the Journal of Experimental Biology on April 11, 2002: Baier, A.; Wittek, B. and Brembs, B. (2002):Drosophila as a new model organism for the neurobiology of aggression? J. exp. Biol. 205, 1233–1240. You can download an offprint of the paper in PDF or read the HTML version (with supplementary material). Only five days later, the behavioral framework was published in the Proceedings of the National Academy of Sciences with the title "Fighting fruit flies: A model system for the study of aggression" (5664–5668; April 16, 2002; vol. 99, no. 8). The Boston Globe even ran a newspaper article on the "Fruit Fly Fight Club".