The male fruit fly is a winged Casanova, pursuing lady flies with a repertoire of song, dance, and well-placed licks that many find impossible to resist. Now, by creating genetically engineered female flies that mimic the male courtship display, researchers have taken important steps toward understanding the biological basis of this complex behavior.
Scientists have long suspected that a gene called fruitless (fru) sets up the brain to produce male courtship behavior in Drosophila melanogaster (ScienceNOW, 13 December, 1996). The cells of males and females read the gene in distinct ways, splicing together different mRNA transcripts to yield different protein products. Researchers hypothesized that this could be the key to male courtship, but until now they had no way to prove it.
In a pair of papers in the 3 June issue of Cell, Barry Dickson and colleagues at the Institute of Molecular Biotechnology in Vienna, Austria, report how they tweaked fru and discovered major changes. Mutant females, which spliced the gene as males do, appeared normal, but their behavior was dramatically altered: They courted female flies, using all steps of the male courtship ritual, short of attempting copulation. Male flies altered to splice fru as females do, on the other hand, barely courted at all. Additional experiments identified a circuit of fru-expressing neurons in the fly brain that appears to mediate courtship and sexual orientation.
Dickson hypothesizes that "behavioral switch genes" such as fru provide a way to hardwire adaptive behaviors into the brain so that an animal can perform them instinctively. Still, he and others caution against extrapolating the results to sexual behavior in humans. "Clearly, we are vastly more complicated creatures than flies, and our common experience tells us that our sexual interests are not irreversibly set by our genes," Dickson says.
"I think it's quite remarkable," says Catherine Dulac, a neuroscientist at Harvard University. The work convincingly demonstrates that a single gene can regulate a complex sequence of behaviors, she notes. The team's "very elegant experiments" represent "a start toward understanding how an innate behavior is laid down in a nervous system," adds Edward Kravitz, a Harvard neuroethologist.