According to a new study, a gene that is linked to courtship behavior among fruit flies works differently in two different species. The study shows how conserved genes, which are the same genes that can be found in different species, do not always function in the same way across species.

'Fru' Courtship Gene in Fruit Flies

The fruitless (fru) gene is common to fruit flies and other species of insects. It has been linked to male courtship behaviors.

The genes' expression and function have been studied by scientists. They specifically looked into Drosophila melanogaster (D. melanogaster) and studied it by either taking it from males or giving it to females. It has been seen that males with the fru gene removed lost some courtship behaviors that were male-specific, while females given the gene gained some courtship behaviors.

Christ Baker, a former doctoral researcher from Princeton and a current assistant biology professor at North Carolina State University, explains that the gene was first discovered in the D. melanogaster. However, it is conserved in different insect species, ranging from mosquitoes to cockroaches to grasshoppers. Earlier experiments also suggest that its function remained conserved across different species.

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Same Courtship Gene With Different Functions Across Species

Now, given how genetic tools have seen incredible advancements, it is now possible to add the gene to the females of other species and see if the gene still operates in the same way. This is made possible with CRISPR-Cas9, specifically.

The researchers chose to examine fru's function in the Drosophila virilis (D. virilis) fruit fly species. This species is quite different from D. melaongaster, as both split apart roughly 60 million years ago. Hence, comparing the two would be like comparing a rat with a mouse. Though they are both fruit flies, similar to how rats and mice are rodents, they are still extremely different from each other.

Like humans, fruit flies contain two gene copies for each one. As part of the "The role of fruitless in specifying courtship behaviors across divergent Drosophila species" study, the researchers started by giving female D. virilis one fru copy. They found that while these females had a 40% less likelihood for mating, the females who mated stayed fertile. For D. melanogaster females with one fru copy, they are also 40% less likely to engage in mating, but those who mate are no longer able to lay eggs.

Such findings show that fru plays a similar role in certain female behaviors, such as mating. However, it has a different role when it comes to other behaviors, such as egg-laying.

Baker explains that D. virilis is quite interesting because of how both males and females have their mating songs. For most species of flies, only the males sing. For D. melanogaster females, when they are given one fru copy, they adopt some courtship behaviors of males, like their singing. However, for D. virilis females with one copy of the fru gene, they kept their ability of female song singing, though they sang more compared to females that did not have the fru gene.

Upon adding another copy of fru to female D. virilis, researchers saw that they could produce male songs while retaining their capacity to produce female songs. On top of this, female D. virilis with two fru copies were fully unreceptive to mating. They also tended to be aggressive towards males that were courting them.

Baker explains that they do not know why it was necessary to add two gene copies in female D. virilis in order to produce results that resemble those from a single copy in the D. melanogaster fruit fly. Nevertheless, this leads to exciting opportunities for further exploration.

The study does show that the conservation of a gene across species does not mean that its function remains conserved. In order to learn more about how the genome could affect development and behavior, it is necessary to study the impacts of genes across various behaviors and species.

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