Summary: Researchers in Japan used genetic engineering to make one species of fruit fly display a courtship ritual normally seen only in another species. By activating the sex-determination “fruitless” gene in insulin-producing neurons, they rewired the brain of Drosophila melanogaster so males offered regurgitated food to potential mates — a nuptial gift behavior characteristic of D. subobscura.
Turning on this single gene produced new neural connections between feeding-related neurons and the brain’s courtship center. The result was a behavioral shift: instead of relying on wing-vibrating courtship songs, modified D. melanogaster males performed a gift-giving ritual. The experiment demonstrates how modest genetic changes in a few existing neurons can generate entirely new behaviors and offers insight into how evolutionary diversity in courtship strategies can arise.
Key Facts
- Behavioral swap: Activation of a single gene converted song-based courtship into gift-giving courtship in D. melanogaster.
- Neural rewiring: Insulin-producing neurons were connected to the brain’s courtship center, enabling the new behavior.
- Evolutionary implication: Small-scale genetic changes in preexisting neurons can drive behavioral diversification between species.
Source: Nagoya University
Japanese researchers have transferred a species-specific courtship behavior from one fruit fly species to another using targeted genetic manipulation.
By selectively activating the fruitless (fru) gene in insulin-producing neurons, the research team induced Drosophila melanogaster males to regurgitate and present food to females — a courtship gift-giving ritual typically found only in Drosophila subobscura. This work, published in the journal Science, is presented as the first demonstration that altering expression of a single sex-determinant gene can form new neural connections and transfer a naturally occurring behavior between species.
In most Drosophila species, males court females by vibrating their wings to produce species-specific courtship songs. D. subobscura, however, evolved a different strategy: males regurgitate crop contents and offer them to females as nuptial gifts during courtship. This gift-giving behavior is absent in closely related species such as D. melanogaster.
Although these two species diverged roughly 30–35 million years ago, both possess the fruitless gene that influences male courtship. The researchers discovered that the presence or absence of fruitless expression in insulin-producing neurons is a key difference: in D. subobscura those neurons connect to courtship control centers in the brain, while in D. melanogaster they normally do not.
“When we activated the fru gene in insulin-producing neurons of singing flies to produce FruM proteins, the cells grew long neural projections and connected to the courtship center in the brain, creating new brain circuits that produce gift-giving behavior in D. melanogaster for the first time,” explained Dr. Ryoya Tanaka, co-lead author and lecturer at Nagoya University’s Graduate School of Science.
To locate the neurons responsible, the team introduced DNA into D. subobscura embryos to produce heat-activated proteins in specific brain cells. By applying heat to activate those cell groups and comparing the brains of regurgitating and non-regurgitating flies, they identified 16–18 insulin-producing neurons that express the male-specific FruM protein, clustered in the pars intercerebralis region of the brain.
“Our findings indicate that the evolution of novel behaviors does not necessarily require the emergence of new neurons,” said Dr. Yusuke Hara, co-lead author from the National Institute of Information and Communications Technology (NICT). “Instead, small-scale genetic rewiring in a few preexisting neurons can lead to behavioral diversification and ultimately contribute to species differentiation.”
“We’ve shown how complex behaviors like nuptial gift-giving can be traced back to their genetic roots,” added senior author Dr. Daisuke Yamamoto of NICT. “This reveals a pathway for how evolutionary shifts in gene expression produce entirely new reproductive strategies that affect survival and reproductive success.”
The study, titled “Cross-species implementation of an innate courtship behavior by manipulation of the sex-determinant gene,” was published in Science on August 14, 2025. The research was led by Drs. Yusuke Hara and Daisuke Yamamoto at NICT, in collaboration with investigators at Nagoya University.
Funding
This research received support from KAKENHI Grant-in-Aid for Scientific Research programs, including grants for early-career scientists and larger projects under Scientific Research A and C, as well as Transformative Research Areas: Hierarchical Bio-Navigation Science (project numbers listed in the original publication).
About this genetics and behavioral neuroscience research news
Author: Merle Naidoo
Source: Nagoya University
Contact: Merle Naidoo – Nagoya University
Image: The image is credited to Neuroscience News
Original Research: Closed access. “Cross-species implementation of an innate courtship behavior by manipulation of the sex-determinant gene” by Ryoya Tanaka et al., Science.
Abstract
Cross-species implementation of an innate courtship behavior by manipulation of the sex-determinant gene
Females of Drosophila subobscura accept courting males only after nuptial gift giving, where a male transfers regurgitated crop contents mouth-to-mouth; this behavior is absent in D. melanogaster. Through clonal activation of neurons expressing the male-specific FruM protein, the researchers identified insulin-like peptide–producing cells (IPCs) and their probable postsynaptic targets — proboscis-innervating motor neurons — as critical components for gift giving.
The study shows that loss of FruM in D. subobscura IPCs prevents neurite extension and abolishes gift giving, whereas overexpression of FruM in the corresponding IPCs of D. melanogaster induces neurite overgrowth, forms functional synapses and increases regurgitation. The authors propose that acquisition of FruM expression by IPCs in an ancestral D. subobscura lineage enabled the latent capacity for nuptial gift giving, illustrating how changes in gene regulation can create new behavioral repertoires during evolution.