Scientists Find “Gay Switch” in Fruit Flies
Posted by shadmia on December 18, 2007
What makes someone straight, gay or even bisexual? Is someone born homosexual or is it a learned behavior? Can sexual orientation be changed or is it hardwired in the brain? Homosexuality has been documented in almost 500 species of animals, signaling that sexual preference is predetermined. However, these questions have been pondered by scientists, moralists, theologists and many others for centuries. It is still an open question – at least for humans anyway.
In the case of the fruit fly the answer is simple. It is a gene – and it can be manipulated. Researchers at the University of Illinois at Chicago led by David Featherstone said they discovered what they call a “gender blind gene,” or GB. GB transports the neurotransmitter glutamate to brain cells. By altering this gene the researchers have shown that they can cause male fruit flies to court other male fruit flies.
“We put the males together, and they did to each other what they do when they’re interested in a female: They approach her, sing her a song, lick her … and mount her,” researcher David Featherstone told ABCNEWS.com.
The researchers then went one step further and put the male flies with the altered gene together with both male and female flies in the same chamber. They found that the altered males were attracted to both sexes with equal frequency. In other words, it did not matter if their partner was male or female. They were bisexual. This same experiment was conducted on female fruit flies with the same results. Females pursued females or males equally.
David Featherstone and his team reasoned that GB mutants might show homosexual behavior “because their glutamatergic synapses were altered in some way”. To test this, they genetically altered synapse strength, independent of GB. They also gave flies drugs to alter synapse strength. As predicted, they were able to turn fly homosexuality on and off, within hours.
“It was amazing. I never thought we’d be able to do that sort of thing, because sexual orientation is supposed to be hard-wired,” Featherstone said. “This fundamentally changes how we think about this behavior.”
In much of the animal kingdom, smells affect sexual behavior. These smells come in the form of chemicals called pheromones. The team figured fly brains maintain two sensory circuits: one to trigger heterosexual behavior and one for homosexual. When GB suppresses glutamatergic synapses, the homosexual circuit is blocked. So they did more tests. As expected, without GB to suppress synapse strength, the flies no longer interpreted smells the same way.
“Pheromones are powerful sexual stimuli,” Featherstone said. “As it turns out, the GB mutant flies were perceiving pheromones differently. Specifically, the GB mutant males were no longer recognizing male pheromones as a repulsive stimulus.”
Does this have any implications for human sexuality? In an experiment it was shown that gays and heterosexuals respond differently to pheromones. There is also some discussion among scientists as to whether a “gay gene” exists in humans. Humans are vastly more complex than the fruit fly but we may have more in common than previously thought.