Threshold-Based Ordering of Sequential Actions during Drosophila Courtship

Goal-directed animal behaviors are typically composed of sequences of motor actions whose order and timing are critical for a successful outcome. Although numerous theoretical models for sequential action generation have been proposed, few have been supported by the identification of control neurons sufficient to elicit a sequence. Here, we identify a pair of descending neurons that coordinate a stereotyped sequence of engagement actions during Drosophila melanogaster male courtship behavior. These actions are initiated sequentially but persist cumulatively, a feature not explained by existing models of sequential behaviors. We find evidence consistent with a ramp-to-threshold mechanism, in which increasing neuronal activity elicits each action independently at successively higher activity thresholds.McKellar et al. show that Drosophila courtship includes a stereotyped behavioral motif consisting of several overlapping actions. These multiple actions are controlled by a single pair of sexually dimorphic descending neurons. These neurons elicit each successive action at progressively higher threshold spike counts.