Complete male fruit fly wiring map connects genes to behavior

Scientists have mapped all 166,000 neurons in an adult male fruit fly’s central nervous system, including its brain, optic lobes and nerve cord. The diagram records millions of connections and can now be compared directly with the adult female brain mapped in 2024.

The comparison shows that most sensory and movement circuitry is shared. Yet a relatively small proportion of cells and connections differs, helping to produce distinct behaviors involving courtship, wing-generated song and aggression. Researchers could also see how two sex-determining genes, fruitless and doublesex, help shape these circuits, filling in a crucial step between genetic instructions and behavior.

The map took about four years to build. High-resolution electron microscopy captured the nervous system in tiny sections, machine-learning tools assembled and traced the images, and specialist human reviewers corrected the results. Related studies used the resource to follow taste signals from receptors around the body toward circuits controlling feeding and movement, and to show that visual processing reaches deep into the brain.

Fruit flies are not miniature humans, and the findings do not explain behavioral differences between women and men. But the work provides a manageable model for studying how genes alter brain wiring. Researchers hope those principles may eventually help investigations of genetic variation associated with conditions including autism and schizophrenia.