Investigating Potential Neural Circuit Mechanisms for Production of Pulse Song in Drosophila melanogaster

Abstract

Animals are required to rapidly generate complex behaviors from limited motor outputs in order to successfully survive and reproduce in a variety of contexts. Sensory cues from an organism’s environment drive highly specific patterning of these motor outputs, allowing them to evade threats, capture prey, and find mates. Acoustic communication is a contextually patterned behavior displayed by numerous species during mating interactions. Many organisms utilize a specific subset of motor outputs to produce sounds that they must manipulate and rearrange to propagate auditory information. However, the neural mechanisms driving the patterning of sound syllables are not well understood in any system, particularly in response to contextual information from the social environment. Drosophila melanogaster is a useful model system to study the latter interaction because males exhibit behavioral patterning through production of courtship song. During courtship, males often generate complex songs composed of three distinct song modes. Females provide social and sensory cues that males integrate to adjust their song in response to these stimuli. Here, we investigated potential neural circuit mechanisms driving the production of slow and fast pulse song in D. melanogaster—two of the syllables or modes of courtship song. Slow pulse and sine song are produced near the female, while fast pulse is produced far from the female. We leveraged single-neuron and combined optogenetic experiments, as well as new connectomic information to build on existing courtship song circuit models by confirming the involvement of neurons within the circuit, identifying other potential candidates, and examining song bout composition to gain insight into which pathways and cell types drive the production of specific song modes. In alignment with previous research, we confirmed that descending neuron cell types pMP2 and pIP10 (neurons that collect information in the brain and send their outputs to the ventral nerve cord (VNC)) largely drive the production of fast pulse song, TN1A (a VNC cell type) drives sing song production, and dPR1 (another VNC cell type) drives nonspecific pulse song generation. Additionally, combined activation of dPR1 and pMP2 with TN1A indicated a cell-intrinsic mechanism for the production of both pulse subtypes. Furthermore, using connectomic tools, we identified four additional candidates for slow pulse song production and two for fast pulse song. Finally, we discovered that proportions of sine song are higher in traces of slow pulse song than fast pulse song, indicating the potential for a similar neural mechanism driving their production. This research provides insight into the complex neural circuit mechanisms that allow species to integrate information from their environment to pattern and produce diverse behaviors.