University of Chicago researchers have found that suppressing a gene called sphinx in fruit flies increases the likelihood of male-male courtship.
The study was purely based on a fly species called Drosophila melanogaster, in which male-male courtship is generally not prevalent at high levels.
A team led by Manyuan Long, a professor of Ecology and Evolution at the university, showed in 2002 that D. melanogaster possessed the sphinx gene, while other fly species did not.
The two million-year-old gene is expressed in male reproductive glands.
With a view to determining the role of this gene, former graduate students in Long's lab named Hongzheng Dai and Ying Chen engineered the flies to have the sphinx gene suppressed.
At first, "the flies looked normal," said Long.
However, when two males lacking the gene were put together, the researchers found males to be "interested in other males".
The same result replicated each time the researchers repeated the experiment.
The researchers revealed that males without sphinx pursued each other more than 10 times longer than did males with a working copy of the gene.
According to them, such insects performed all stages of normal male-female courtship-orienting, tapping, singing, licking, attempting-except for copulating.
"The absence or presence of the sphinx gene appears to regulate the diversity of male-male courtship behaviour among flies. This suggests that the genetic control of male courtship is an evolving system, which can recruit new genetic components and change courtship behaviours," Long said.
"This is the genetic interpretation. Of course other factors, like the environment, are also likely to have an influence," Long added.
The researcher also said that groups of males without a working copy of sphinx often formed chains of flies positioned behind each other, which is a typical male-male courtship behaviour that is not seen in male-female relations.
The study also showed that deactivating sphinx in female flies did not result in any changes in reproductive behaviour.
Its authors said that the finding was not surprising because the sphinx gene is not expressed in female reproductive tissues.
Long revealed that sphinxless males were more interested in each other than in females, but would return to the females when they could not complete the copulation process with other males.
"Sphinx is not a protein-coding gene, but an RNA gene. So, the question is: How do RNA genes interact and regulate other genes? We are exploring this in our lab," Long said.