Each member within animal groups decides whether they attack other conspecific members or not, based on their physiological states and social context. For example, members form a group and cooperatively work for foraging and parental care. But sometimes, members fight each other to compete for limited resources, such as food, mating partner and territory. Thus the regulation of aggressive behavior is important to achieve social adaptation. However, the neural basis underlying the social decision-making of aggressive behavior has been largely unknown.
I have focused on aggressive behavior in medaka fish, because Magnuson's paper reported that the attack frequency changes depending on population density. It showed that High population density decreases the attack frequency. So, it is possible that medaka fish has ability of decision-making of aggressive behavior according to population density. Further more, medaka fish is model animal in molecular genetics. So, medaka fish is a suitable animal model for analysis of the neural basis underlying the social decision-making of aggressive behavior.
First, we compared frequencies of medaka aggressive behavior between Cab and drR strains, commonly used in molecular genetics. The attack frequency of Cab strain was significantly higher than that of drR strain. Next, we examined the effect of population density on the attack frequency in Cab strain. At the same time, using CRISPR/Cas9, we generated medaka mutant of some candidate genes, which are predicted to be involved in aggressive behavior.