In many species, ranging from fruit flies to humans, violence and innate aggression are exhibited more often by males than by females. Two main questions that stem from this observation are
- What is the mechanism from which the male-specific aggressive behavior arises?
- Can we manipulate the mechanism to attenuate aggression in males?
The laboratory of Dr. Kenta Asahina at the Salk Institute for Biological Studies is interested in answering the aforementioned questions by studying aggression and violent behavior displayed by male fruit flies (Drosophila). In his paper titled “Tachykinin-Expressing Neurons Control Male-Specific Aggressive Arousal in Drosophila” published in 2014, Dr. Asahina et al. discovered a group of fruitless-expressing neurons (i.e. FruM+ neurons) that promote/enhance male-specific aggression in male fruit flies . More interestingly, Dr. Asahina et al. showed that these neurons are sexually dimorphic and do not affect the courtship behavior between males and females.
Using “thermo-genetics” (using thermo-sensitive channels to activate a certain group of neurons), Dr. Asahina et al. first identified two lines of tachykinin-expressing (Tk-GAL4) neurons that significantly increased aggression in male Drosophila. In order to verify that these neurons are indeed required for male-specific aggression, the group compared the number of lunges (a measure of aggression) during thermogenetic activation and inactivation of the neurons as shown in Figure 2 I (activation) and J (inactivation).
(Figure 2 from )
Furthermore, the group investigated if activation of these neurons affected courtship behavior and induced any aggressive behaviors displayed by male fruit flies toward female flies. Interestingly, the thermogenetic manipulation did not significantly influence the male-female courtship behavior.
Next, to unravel the mechanism behind male-specific aggression, Dr. Asahina et al. studied the role of the Tk gene product, DTK peptides. Deletion of the gene Tk (via FLP chromosome translocation) resulted in a strong attenuation in the number of lunging, suggesting that DTK peptides are required for normal levels of male-specific aggression. In addition, they discovered that the effects of Tk in the Tk-GAL4 neurons are required for male-male aggression.
 Asahina, Kenta, Kiichi Watanabe, Brian J. Duistermars, Eric Hoopfer, Carlos Roberto González, Eyrún Arna Eyjólfsdóttir, Pietro Perona, and David J. Anderson. “Tachykinin-Expressing Neurons Control Male-Specific Aggressive Arousal in Drosophila.” Cell 156.1-2 (2014): 221-35. Web.
Robert Kim is a first-year graduate student in the neurosciences graduate program and a member of Dr. Terrence J. Sejnowski’s lab.