Trans-sexually grafted antennae influence development of sexually dimorphic neurones in moth brain

Observations in insects reveal sexual differences in the central nervous system (CNS), associated with sexually dimorphic patterns of reproductive behaviour^1-9. For example, in certain species of moths, including the sphinx moth Manduca sexta, only males fly towards a sexually receptive female or towards a source of the female sex pheromone^10,11. In Manduca, specialized olfactory receptor cells found only on male antennae^12,13 respond sensitively and selectively to the female sex pheromone (unpublished experiments with K.-E. Kaissling and R. J. O'Connell). Their axons project into the macroglomerular complex (MGC), which is characteristic of male, but not female, antennal lobes (ALs; Fig. 1b, d)^1-3,5,8,9,14. These afferents to the MGC presumably synapse with male-specific AL neurones^8,15 to begin the processing of phenomonal information. We have now devised a surgical procedure for producing antennal gynandromorphs of Manduca in which one of the two ALs receives sensory innervation from an antenna formed by a transplanted imaginal disk of the opposite sex. We report here that in these gynandromorphs, the physiological and morphological properties of certain AL neurones are influenced by the gender of the antennal sensory axons contacting them. In particular, neurones resembling the male-specific AL neurones appear in female ALs innervated by sensory axons from a grafted male antenna.