Sound and fury: Modulation of aggressive behavior through acoustic signals

In any sexually reproducing animals, one expects aggressive encounters to occur between/among males because of their adaptive value; competition over resources (food, territory, mates, social status) plays a critical role in both natural and sexual selection in most species of animals (1, 2). Male–male interaction, when behaviorally enacted, is labeled as aggression, and it varies in expression from subtle gestures to outright physically combative encounters. Moreover, aggressive behavior is usually mediated by species-specific signals in one or more sensory modalities. In PNAS, Versteven et al. (3) continue the study of intermale acoustic signals in Drosophila melanogaster [e.g., Jonsson et al. (4)], advancing it by providing neurosensory mechanistic data by deploying classic lesion as well as genetic methods to probe the role of the fly’s “ears” in expressing aggressive behavior. The authors (3) show that the ability of hearing can affect the behavioral outcome of dyadic male–male encounters in laboratory contest arenas. The auditory basis of hearing in D. melanogaster has been subject to numerous studies at multiple levels of biological organization over many size scales (5). The auditory hearing organ, known as Johnston’s organ (JO), is the modified second segment of the antenna. Previous work has shown that the JO is stimulated by sound-induced vibrations, such as airflow from the beating wings of a nearby fly. The salient acoustic signals for communication are produced by the male extending one wing and briefly fluttering it at the target receiver fly. This stereotyped gesture takes place with the sender and receiver at very close proximity, within one or at most two body lengths. The JO is easily visible and very accessible for experimental manipulation, which made deafening the fly relative easy using classic techniques that prevent acoustic vibrations from setting the JO into motion or simply ablating it (figure 1 in …