Missing gene renders fruit flies clueless about sex

The signals they're missing are pheromones wafting from mated females and male flies. These signals are so important to the flies that they are hardwired into the processing centre of the fly's brain, which governs behaviour.

This direct connection surprised the scientists, who have studied other fruit fly courtship genes. "It goes against the dogma that was established for the olfactory and taste systems," said Hubert Amrein, of Duke Department of Molecular Genetics and Microbiology.

"Our finding implies that signals from the outside don't have to go through processing stations in the chemosensory system before being connected to the higher-order brain structures."

Males without a gene called Gr32a, the gustatory receptor gene, showed normal levels of courtship with virgin females. But in competition with normal (or wild-type) male fruit flies, they were outperformed 4 to 1. In fact, the Gr32a-lacking flies courted the male competitors in addition to the females.

The scientists also found that the males lacking the Gr32a gene courted females who had already mated. Wild-type males, however, were did not try to target mated females, because the latter have received male pheromones during the first mating.

The hapless Gr32a-negative males tried to mate with virgin females even when they had been covered with male pheromones, behaviour that the wild-type flies avoided.

"This gene was very powerful for distinguishing between genders and for determining mating status," said co-author Tetsuya Miyamoto, of the same department.

"Male pheromone is so effective that Gr32a mutants court males with almost the same intensity as they do females."

The GR32a gene is not found in humans. "In general, the development of pheromones in human sexual behaviour is not as clear-cut as one would hope," Amrein said.

The work appears online in Nature Neuroscience.St/jg

(375 Words)26071507NNNN (IANS)

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