Layered roles of <i>fruitless</i> isoforms in specification and function of male aggression-promoting neurons in <i>Drosophila</i>.

Abstract

Inter-male aggressive behavior is a prominent sexually dimorphic behavior. Neural circuits that underlie aggressive behavior are therefore likely under the control of sex-determining genes. However, the neurogenetic mechanism that generates sex-specific aggressive behavior remains largely unknown. Here, we found that a neuronal class specified by one of the <i>Drosophila</i> sex determining genes, <i>fruitless</i> (<i>fru</i>), belongs to the neural circuit that generates male-type aggressive behavior. This neuronal class can promote aggressive behavior independent of another sex determining gene, <i>doublesex</i> (<i>dsx</i>), although <i>dsx</i> is involved in ensuring that aggressive behavior is performed only toward males. We also found that three <i>fru</i> isoforms with different DNA binding domains show a division of labor on male aggressive behaviors. A dominant role of <i>fru</i> in specifying sex-specific aggressive behavior may underscore a genetic mechanism that allows male-type aggressive behavior to evolve at least partially independently from courtship behavior, which is under different selective pressures.