On the Role of the Protocerebral Bridge in the Central Complex of Drosophila melanogaster Brain in Control of Courtship Behavior and Sound Production

To elucidate the role of the protocerebral bridge (PB) of the brain central complex of Drosophila melanogaster in control of courtship behavior and singing, a comparative study have been performed of characteristics of courtship behavior and parameters of male sound signals in wild type flies (Canton S) and in flies from 3 mutant strains having anatomical defects in the PB: oc ₁ (the PB is absent), nob _KS49 (the midline PB glomeruli 1–3 are missing), and cex _KS181 (tangential input fibers to the PB are evidently missing or reduced). It has been shown that the PB is involved in control of the accuracy of movements of males during courtship to a female and in control of the form and stability of sound elements forming the courtship songs. The rhythmic structure of the courtship songs, which is determined by the stability of the pacemaker activity, is controlled by other central complex substructures. Thus, the nervous circuits determining the form of sound elements and the rhythm of their repetition are separated and are under control of different brain centers. Since the distortions of sound signals in mutants are temporary, it is concluded that the thoracic song center contains all necessary elements for generation of normal courtship signals, whereas the brain centers produce only modulating influences on their parameters in correspondence with the context of the external situation.