Neural Circuits of Sexual Behavior in Caenorhabditis elegans.

The recently determined connectome of the Caenorhabditis elegans adult male, together with the known connectome of the hermaphrodite, opens up the possibility for a comprehensive description of sexual dimorphism in this species and the identification and study of the neural circuits underlying sexual behaviors. The C. elegans nervous system consists of 294 neurons shared by both sexes plus neurons unique to each sex, 8 in the hermaphrodite and 91 in the male. The sex-specific neurons are well integrated within the remainder of the nervous system; in the male, 16% of the input to the shared component comes from male-specific neurons. Although sex-specific neurons are involved primarily, but not exclusively, in controlling sex-unique behavior-egg-laying in the hermaphrodite and copulation in the male-these neurons act together with shared neurons to make navigational choices that optimize reproductive success. Sex differences in general behaviors are underlain by considerable dimorphism within the shared component of the nervous system itself, including dimorphism in synaptic connectivity.