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Why Some Male Flies Don’t Mate
By Donna Bernstein

Scientists have discovered a gene that is directly responsible for sexual behavior in fruit flies. The gene is essential for sexual reproduction and therefore the survival of the species.

This figure shows the mating ritual of fruit flies. The process starts with initial contact between the flies. The male then taps the female, extending and vibrating his wings. Next, he licks the abdomen of the female fly. Finally, they copulate.

Some animals, including fruit flies and mice, send out chemical messages called pheromones to signal sexual attraction and mating. Although scientists and perfume companies have long searched for these chemical signals, the specific responses to pheromones have remained elusive until now.

Researchers at Duke University Medical Center in Durham, North Carolina, found that if the receptor for a specific pheromone is not working properly, males do not complete the mating ritual. Mutant males fail to recognize a female's signal and do not go all the way, the scientists report in the journal Neuron.

Like men and women, fruit flies (Drosophila melanogaster) have complicated courtship customs. When the male fly sees an attractive female, usually near their feeding territory (perhaps the fly equivalent of a bar or restaurant), he follows her until he gets the signal to approach. Soon he brushes her with his foreleg in a gentle tap, essentially putting one of his six arms around her.

When the female is responsive and sends him the chemical green light, he presents his courtship song by vibrating his wings. (For human courtship, Sting or the Beatles are effective.) When the female allows him to explore her with his tongue (in flies it's called a labellum), he knows he'll score. What happens next may not be appropriate for publication, but the mating is a success.

Duke scientists Steven Bray and Hubert Amrein found the gene for the fly's foreleg receptor that reads the signal to move to the next stage of the mating process only in males. The gene, called Gr68a, and 70 genes of that class were identified in the fly genome sequence; all are distantly related to genes for olfactory receptors.

If the pheromone receptor gene is impaired, the fly stalls at the leg-brushing stage, never gets to first base, and the seduction is a fiasco. The inactivation of the gene results in a significant reduction in male courtship performance, the researchers say.

However, flies with the defective pheromone receptor are in every other respect like normal males.

—Related Stories—

Scents and Pheromones

Survivor in the human genome

Sex drive and aggression linked to pheromone receptor genes in mice

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Bray, Steven and Amrein, Hubert. A Putative Drosophila Pheromone Receptor Expressed in Male-Specific Taste Neurons Is Required for Efficient Courtship. Neuron 39 1019-1029 (September 11, 2003).

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