Sexually dimorphic neurons of the terminalia of Drosophila melanogaster: II. Sex-specific axonal arborizations in the central nervous system.

In order to understand how the peripheral nervous system in male and female flies differ, I have determined the projection pattern of sensory neurons that innervate the sex-specific adult terminalia, the genitalia and analia, of Drosophila melanogaster. In the adult male and female fly, mechanosensory bristles arranged on the external terminalia are innervated by sensory neurons that arborize in the abdominal ganglion. The distribution of axonal arbors differs between males and females. In males, sensory neurons terminate in a greater variety of patterns over a larger area of neuropil than those in females. Mutations in a sex-determining gene (transformer-2, tra-2,) which regulates the development of secondary sexual characteristics in somatic tissues, cause female flies to be transformed into phenotypic males. The sensory neurons of the terminalia are also transformed leading them to arborize appropriately for male neurons.