A common species of fruit fly, Drosophila subobscura, has a peculiar mating ritual. To accept copulation, the female requires the male to regurgitate food directly into her mouth. It is an innate behavior, not observed in other species of fruit fly, such as Drosophila melanogaster, whose males court the female with the vibration of their wings.
About 30 million years of evolution separate the two species. But a team of Japanese scientists has now managed to transfer the regurgitation ritual from one species to another with a simple genetic modification. In a lab at Nagoya University, male Drosophila melanogaster have begun regurgitating into the mouths of females before copulating. The researchers say that this is the first time a behavior has been transferred between species by manipulating a single gene.
Both species share a strand of DNA, the fru gene, which controls the behavior of males during courtship. However, some behaviors consist of producing romantic sounds and others to offering regurgitated bridal gifts. The scientists, led by geneticist Daisuke Yamamoto, observed that, by hyperactivating the gene in a group of neurons in Drosophila melanogaster, these cells develop long projections that create new brain circuits and generate regurgitation behavior. Their results show that a small reconfiguration of neurons is enough to revive ancestral behavior. The study was published August 14 in the journal Science.
In March 2023, Spanish biologist Albert Cardona and his Croatian colleague Marta Zlatic presented the first complete map of an animal brain, which happened to be that of the larva of the fly Drosophila melanogaster. A year later, an international consortium obtained the map of the adult Drosophila melanogaster’s brain: 140,000 neurons, with about 55 million connections between them. Cardona believes that the new study “is very interesting, but, although it seems new, it isn’t all that new.” The biologist recalls that two years ago the neuroscientist Tomoko Ohyama showed that by manipulating the activity of a neuron in the larvae of Drosophila melanogaster she could reproduce the flight behavior characteristic of another species of fly, Drosophila santomea, whose larvae escape by rolling away from harmful stimuli.
Cardona, who works at the Molecular Biology Laboratory in Cambridge, explains that he and another Spanish biologist working in the United Kingdom, Lucía Prieto Godino, published the preliminary results of similar research in June. The authors mapped the neural circuitry of the olfactory system of the fly Drosophila erecta, an insect endemic to West Africa that feeds exclusively on the fruits of a tropical shrub. After analyzing the mechanism of this insect, the team genetically manipulated the neural connections of the fly Drosophila melanogaster so that it was also partial to the African fruit.
Cardona says it is a shame that the Japanese study does not cite these two precedents but recognizes the value of the new results. “What should be noted is that, although separated by 30 million years, the two species of fly, Drosophila melanogaster and Drosophila subobscura, are capable of the same behavior ― sharing a nuptial gift [regurgitated food] ― but while it does not occur naturally in one, it does in the other. This gives rise to speculation that evolution does not have to form new circuits, but merely to tune the intensity of the connections between neurons, and this is enough to change behavior, as first described by Tomoko Ohyama and Lucía Prieto Godino,” says Cardona.
Prieto Godino directs a laboratory at the Francis Crick Institute in London that investigates the evolution of neural circuits: the connections between cells on which thoughts, memories and behaviors depend. Godino is impressed by the study that has transferred the ritual of regurgitation from one species of fly to another. “This work shows that potentially simple genetic changes ― such as a change in the expression of a gene in neurons that do not normally express it ― can alter how these neurons connect with the rest of the circuits, and how that in turn can change behavior,” she says.
Yamamoto, of the National Institute of Information and Communications Technology in Kobe, explains why he believes his study goes further than previous ones. “We have managed to transfer an entire pattern of behavior from one species to another by manipulating a single master gene that controls a specific behavior,” the geneticist tells EL PAÍS. “As far as I know, it is the first time it has been done. Previous work had induced changes in the intensity of a response or in preferences or dislikes, but not in the repertoires of behaviors themselves.”
Biotechnologist Lluís Montoliu from the National Centre for Biotechnology (CSIC) in Madrid is excited about the implications of the new study. “It is a surprising article, one of the first ― if not the first ― to identify what would be the genetic basis of what we call innate behaviors, which we assume we understand, when this is not the case. These are behaviors that are transmitted from generation to generation, that do not require learning and that cause certain species to behave in one way or another, such as, for example, during courtship,” he explains.
“It shows that this innate behavior is not the product of magic, it is not the product of something inexplicable, but is something that is inscribed in the genes and not only in the genes, but also in where these genes are expressed,” Montoliu adds.
Montoliu stresses that it is the same gene that controls the seductive sounds emitted by Drosophila melanogaster and the regurgitations offered by Drosophila subobscura. “The change is not in the gene but in its ability to express itself. This work demonstrates the power of epigenetics,” he explains, referring to the chemical modifications of DNA that alter how the same gene is read in different cells. “Hats off to this study. We now know that an innate behavior is inscribed in genetics, not due to the presence of new genes, but to the expression of the same gene in a new territory.”
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