Drosophila subobscura males regurgitate food and offer it as a gift to females during courtship. (Credit: Tanaka et al., 2025)
In A Nutshell
- Male Drosophila subobscura woo females with a regurgitated “nuptial gift,” a behavior absent in D. melanogasterexcept on rare occasions.
- Researchers pinpointed insulin-producing brain cells (IPCs), normally involved in feeding, as the neural hub for this behavior.
- By adding expression of the FruBM protein to D. melanogaster IPCs, scientists induced gift-giving behavior in this species.
- The work shows how small genetic tweaks can repurpose existing brain circuits for entirely new social behaviors.
NAGOYA, Japan — Researchers have pulled off what might be the ultimate biological matchmaking experiment: they’ve successfully transplanted a bizarre courtship ritual from one fruit fly species to another by altering where a single gene is switched on in the brain. The breakthrough sheds new light on how evolution invents new behaviors and could help scientists understand the genetic basis of social interactions.
During courtship, male Drosophila subobscura fruit flies regurgitate food from their crop and present it to potential mates as a “nuptial gift.” Females who accept this offering extend their proboscis (a tube-like mouthpart) to consume the gift before mating. Among the dozens of Drosophila species studied, D. subobscura is the only one known to require this behavior for mating — although D. persimilis males occasionally do something similar, it’s not essential for them to win over a mate.
D. subobscura split from its more common cousin, D. melanogaster, roughly 30 to 35 million years ago. Since then, D. subobscura evolved this unusual courtship strategy while D. melanogaster stuck to more familiar techniques like wing displays and courtship songs.
Tracking Down the Brain’s Romance Center
The research team, led by Dr. Ryoya Tanaka from Nagoya University and Drs. Daisuke Yamamoto and Yusuke Hara from Japan’s National Institute of Information and Communications Technology, used genetic tools to pinpoint which brain circuits control nuptial gift giving. They engineered D. subobscura flies with temperature-sensitive ion channels (dTrpA1) that let them activate small groups of neurons simply by warming the flies and watching for regurgitation.
Through systematic testing, they identified insulin-like peptide–producing cells (IPCs), neurons usually involved in metabolism and feeding, as key players. Artificially activating IPCs made males regurgitate more often; blocking them reduced regurgitation frequency. Crucially, they found that D. subobscura IPCs express the male-specific protein FruM, a product of the fruitless gene that drives many male courtship behaviors. D. melanogaster IPCs do not express FruM.
Drosophila subobscura males regurgitate food and offer it as a gift to females during courtship. (Credit: Tanaka et al., 2025)
Engineering Romance Across Species
With that insight, the team took a bold step: they induced expression of a specific FruM isoform, FruBM, in D. melanogaster IPCs.
The results, published in Science, were very exciting. The modified D. melanogaster developed elongated neural connections resembling those in D. subobscura. More importantly, some began regurgitating during courtship — a behavior that, while rare in wild-type D. melanogaster, became much more common in the modified flies. Males often timed the regurgitation to coincide with licking female genitals, closely mimicking D. subobscura’s nuptial gift behavior.
When females were given a choice, they preferred males with activated IPCs over unmodified males, suggesting the behavior offered a competitive mating edge. The team also traced how signals from courtship-initiating P1 neurons reach the IPCs, which then coordinate proboscis extension and crop contractions to deliver the gift.
The researchers identified 16-18 insulin-producing neurons in Drosophila subobscura that express the male-specific protein FruM. When they activated FruM expression in insulin-producing neurons in D. melanogaster, these cells grew new neural connections and successfully transferred gift-giving courtship behavior to this species for the first time. (Credit: Tanaka et al., 2025)
How Evolution Hijacks Existing Systems
Rather than creating new neural circuits from scratch, evolution seems to have repurposed existing feeding and metabolic control systems for romantic purposes. In D. subobscura, IPCs that usually help regulate food intake were recruited into the courtship circuit through the acquisition of FruM expression.
“We suggest that the acquisition of FruM expression by IPCs was a key event occurring in an ancestral D. subobscura that conferred a latent capability to perform nuptial gift giving, in which regurgitation plays a central role,” the researchers wrote.
In D. subobscura, these insulin cells have evolved longer, more elaborate neural projections, allowing them to connect with motor neurons controlling the proboscis and send signals to the crop to push food upward for regurgitation.
Beyond Fruit Fly Romance
While fruit fly romance might seem trivial, the research offers a window into how complex social behaviors can evolve from modest genetic changes. By shifting when and where a single gene is expressed, evolution can redirect existing neural hardware to new purposes, or in this case, turning a feeding circuit into a mating display.
“Our findings indicate that the evolution of novel behaviors does not necessarily require the emergence of new neurons; instead, small-scale genetic rewiring in a few preexisting neurons can lead to behavioral diversification and, ultimately, contribute to species differentiation,” Dr. Hara says in a statement.
Similar processes may underlie the evolution of social behaviors in other animals, including mammals. This study is also a rare case of scientists successfully transferring an innate behavior between species, demonstrating the precision with which modern genetic tools can dissect and re-engineer the biological basis of behavior.
Paper Summary
Methodology
Researchers used clonal activation of FruM-expressing neurons in D. subobscura to identify brain cells involved in nuptial gift giving. Thermogenetic activation allowed selective stimulation of small neuronal groups. Two groups — IPCs and L-pSG neurons — were more often active in regurgitating males. Antibody staining, electrophysiology, and behavioral assays were used to characterize these neurons. FruBM was expressed in D. melanogaster IPCs to test whether the behavior could be induced across species.
Results
In D. subobscura, IPCs express FruM and are essential for nuptial gift giving. FruBM overexpression in D. melanogaster IPCs extended dendrites, increased regurgitation during courtship (including during licking), and improved copulation rates under competitive conditions. The study mapped a P1 neuron → IPC → motor pathway that supports regurgitation and crop control during gift delivery.
Limitations
Although D. subobscura and D. melanogaster were the main experimental species, the work also considered other Drosophila species in a phylogenetic comparison of nuptial gift giving. Mosaic activation targeted small neuronal sets, so other components of the circuit could have been missed. Because regurgitation also occurs after feeding, careful analysis was needed to distinguish nuptial gifts from other forms of regurgitation.
Funding and Disclosures
Funded by Grants-in-Aid for Scientific Research from Japan’s Ministry of Education, Culture, Sports, Science and Technology. Authors declared no competing financial interests. Materials and genetic constructs available on request.
Publication Information
“Cross-species implementation of an innate courtship behavior by manipulation of the sex-determinant gene” was published in Science on August 14, 2025, by Ryoya Tanaka, Yusuke Hara, Kosei Sato, Soh Kohatsu, Hinata Murakami, Tomohiro Higuchi, Takeshi Awasaki, Shu Kondo, Atsushi Toyoda, Azusa Kamikouchi, and Daisuke Yamamoto. DOI: 10.1126/science.adp5831.