Let’s Talk About (Fruit Fly) Sex

by Katie Pratt

The fruit fly Drosophila melanogaster has been the preferred model system for the study of numerous biological processes for decades, if not centuries. These little beasts are amenable to genetic manipulation, are relatively easy to keep in captivity, and have all sorts of physical traits that make them useful to scientists. Even though I work with frogs, I spend at least half my time reading about flies.

But I don’t usually read about fruit fly sexy times, so today I made an exception, and read a paper about what lady Drosophila do after getting jiggy. It caught my eye mostly because one of the labs upstairs studies fruit fly courtship, so I’ve been lucky enough to watch many videos of these insects flirting. I was even introduced to the difficulty of trying to record them singing their mating songs over the hum of the building’s air conditioning. Just look at them go:

As you can see, it’s a fairly elaborate process. It’s also a highly orchestrated one, and the genes that control these behaviors have been very carefully mapped out. And here’s another part of Drosophila biology I love; the names of the genes. Doublesex, fruitless, pickpocket, Sex Peptide…OK so that last one is a bit lame. Anyway, these genes all interact in specific neuronal circuits to direct the courtship behaviors of both males and females.

After sex, however, these behaviors are markedly changed in the female fly. She no longer runs around coyly, looking back over her shoulder at the persistent male, and tapping her dainty feet provocatively. Instead, she puts all her efforts into laying her now fertilized eggs.

In a recent paper published in Current Biology, scientists from the Universities of Oxford and Glasgow and Harvard Medical School have shown on a molecular level how this post-mating behavior is controlled in the nervous system of the female fly. Genes previously implicated in courtship behavior, doublesex and fruitless, are expressed in neurons in the uterus. When the male ejaculates he deposits Sex Peptide along with his sperm. This small protein binds to receptors on the uterin neurons, which in turn relay a signal to the fly’s brain. Importantly, they then tracked the responses in the brain, and found that the mating signal was passed along to neuronal circuits controlling the physical aspects of egg-laying.

But what does this all mean?? It means that fruit flies are a fantastic model system for understanding the neural circuitry underlying complex behaviors (among many other things), and that Drosophila research will be a mainstay of biology departments the world over, no matter what Sarah Palin thinks.

Katie Pratt is a graduate student in Molecular Biology at Brown University. She has a passion for science communication, and in an attempt to bring hardcore biology and medicine to everyone, she blogs jargon-free at www.katiephd.com. Follow her escapades in the lab and online on Twitter.

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