Figure 3.

Proposed circuitry underlying the initiation of courtship and pulse song in the male CNS. During courtship, a male extends and vibrates his wing to sing a species-specific courtship song. Five distinct fru-expressing clusters of neurons that consist of command/decision-making neurons (P1), descending interneurons (pIP10), and components of the central pattern generator (dPR1, vPR6 and vMS11) are thought to form an interconnected circuit [26^•]. Thermoactivation of these neurons triggers wing extension and/or vibration in isolated males deprived of the sensory inputs that would normally induce males to sing [26^•]. Thermoactivation of P1 and the descending neuron P2b independently initiate male courtship in the presence of a female. Sensing volatile and/or contact pheromones subsequently alters the activity of the P1 cluster, suggesting its capability of integrating olfactory and gustatory sensory cues when making the decision to court. Thus P1 and P2b are thought to play a key role in triggering male courtship [53^••]. Although the descending cluster, P2b, is connected to P1 neurons its downstream connections within the VNC have yet to be identified. A cluster of flight muscle motoneurons, vMS2, may (dotted line) form connections with the CPG [19^•]. Note that only half of the male CNS is shown in the schematic.

Adapted from [61].