14 DAY TRIAL // Homosexuality is regarded as unnatural, but that's nonsense: nature abounds in examples of homosexual behavior in animals.
Various biological hypotheses say that the genes conferring homosexuality in human and animal males could deliver more fertile female offspring and the genes that confer high masculinity can produce lesbian female offspring. Vice versa, genes of high femininity can render homosexual male offspring.
Males can have some social advantages through homosexual behavior, by gaining support and increasing their chances of copulating females. When a species is mostly bisexual, homosexual relationships allow an easier way to join a pack. Homosexual sex can sometimes train infants for adult sexual roles.
But, the biological basis for homosexuality is still a puzzle. A new research, made by a team led by neuroscientist David Featherstone, professor of biological sciences at the University of Illinois, at Chicago, and published in the online journal "Nature Neuroscience", found that sexual orientation in fruit flies was determined by a previously unknown regulator of synapse strength. The team could genetically manipulate or use drugs in order to activate/deactivate the flies' homosexual behavior within hours.
The team discovered a gene in fruit flies named "genderblind", (GB) whose mutation made the flies bisexual. The gene had the odd ability to carry the neurotransmitter glutamate out of glial cells (auxiliary nerve cells). Variation in the glutamate levels outside cells influenced the strength of nerve cell synapses, crucial in human and animal behavior. But, all the GB mutant male flies were making advance to other males.
"It was very dramatic. The GB mutant males treated other males exactly the same way normal male flies would treat a female. They even attempted copulation." said Featherstone.
Other genes impairing sexual orientation act differently, influencing the brain development into a genetically male or female one. GB could explain why males prefer females for mating; the male mutants could have stronger synapses.
"Based on our previous work, we reasoned that GB mutants might show homosexual behavior because their glutamatergic synapses were altered in some way. Homosexual courtship might be sort of an 'overreaction' to sexual stimuli," said Featherstone.
The team genetically engineered the synapse strength independent of GB, and also used, on flies, chemicals that influenced synapse strength. These could activate/deactivate homosexuality in flies in just some 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," said Featherstone.
The team believes that adult fly brains have dual-track sensory circuits, one activating heterosexual behavior, the other homosexual. When GB shuts off glutamatergic synapses, the homosexual circuit is stopped. The investigation found that with no GB to lower synapse strength, the flies changed the way they detected smells.
"Pheromones are powerful sexual stimuli. 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. It may someday be possible to domesticate insects such as fruit flies and manipulate their sense of smell to turn them into useful pollinators rather than costly pests." said Featherstone.