New research on fly mating habits offers lessons about genetics

Did you know that male fruit flies sing to get the attention of the ladies? New research suggests that fruit flies can even adjust their singing to suit their audience. CBC Radio science columnist Torah Kachur explains why that's a big surprise.

What looks like intelligence may actually be in the genes

New research suggests the mating behviour of fruit flies is largely based on genetics. (Mr. Checker/Wikimedia Commons)

Did you know that male fruit flies sing to get the attention of the ladies? New research suggests that fruit flies can even adjust their singing to suit their audience. CBC Radio science columnist Torah Kachur explains why that's a big surprise.

What does fly courtship look like? 

Fruit flies (known more formally as Drosophila melanogaster) actually have very complex courtship behaviour — and in some ways, it sounds a lot like what humans do.

It begins with the male fly approaching the female — the so-called orientation phase. Then the male sings a little "song" by rubbing his front legs together, to see if the female is receptive. If she is, she will release some pheromones — chemicals that have a scent that basically says, "Okay, I'm interested."

That's when the dance becomes the real deal — and copulation is attempted, and hopefully (for the flies) successful. 

What's amazing about this dance is that it's always the same and it's not a learned behaviour — it's genetically programmed.

What does a fruit fly's love song sound like?

It sounds kind of like a mix between between a mosquito buzzing and a cat purring.

The sound is actually well below our normal hearing range, and has to be altered to be audible to our ears.

But this video from the University of Leicester does that, and you can hear in it what the fruit fly's song sounds like.

What does the latest study tell us about fruit fly mating? 

A new study — published in the journal Neuron — shows that the male fruit fly has the ability to recognize how far away the female is. He'll then adjust the volume, or amplitude, of his mating sound accordingly.

And that's actually a very significant finding. As humans, we naturally regulate the loudness of our voices if we're chatting in a  quiet sitting room or shouting at a concert, for example.

We understand how far away someone is, the overall noise level of the room and how to adjust our volume accordingly. This requires quite complex neural circuits.

It turns out fruit flies share this trait. They have the innate ability to judge how far away the female is, and therefore how loud they should sing. 

"This kind of behaviour has only been identified in humans and songbirds — so relatively complex organisms," said lead researcher Pip Coen, from University College London.

"The fruit fly has only 100,000 neurons — so that's about one-millionth of the human brain. And so it's surprising and exciting that they're able to perform these same complex transformations on the signals they're producing."

What's really fascinating about all of this is not that the flies can learn to adjust volume, but that they do it innately. Fly behaviour is intrinsically encoded in their genes.

How do the fruit fly genes control behaviour?

That is something that has fascinated scientists for decades — how does something that seems so cerebral ultimately get programmed at the level of DNA? 

There are lots of ways that genes control our behaviour — or a fruit fly's.

In the example of the fruit fly mating ritual, there have been some key genes identified. There's one called the fruitless gene. When that particular gene mutates, it changes the neural circuitry of the fly brain so that males hear the male courtship song and are attracted to it. That results in males courting other male flies.

Male-male courtship activity in fruit flies is shown in a courtship chain in this photo from a study by the National Institute of Neurological Disorders and Stroke. (Proceedings of the National Academy of Sciences)
If you have a tube full of these mutants, you get this little conga line of males courting males. And trust me, it's quite the sight.

There are mutant genes for almost every step of the mating ritual, suggesting that there are master controller genes responsible for the ritual, and then smaller players that make the female receptive — allowing her to release pheromones, and to interpret the song as attractive, for example. 

It comes down to the genes programming the brain to be ready to act and learn these signals.

What does this research tell us about humans?

You'd be surprised how similar humans are to flies when it comes to the ways genetics shape our behaviour.

Human behaviour has a huge genetic component. For a long time, it was believed our brains were mostly responsible for our behaviour. But more and more research is challenging that belief.

Take, for instance, studies on identical twins who were separated at birth. They often have similar personalities and tendencies. This suggests behaviour may be more in the genes than something that you learn.

As for our mating dance — genetics may play a bigger role in our mate choice than a good sense of a humour and an adventurous spirit do.

There have been a lot of studies to show that the sense of smell in mate choice is very important as a way to assess the genetic diversity in the immune system of a potential mate. This ensures that the offspring will have the best ability to fight of infections.

There was even a recently published study that says the genetics of height are a major determinant of mate choice, which is why most couples are roughly the same height.

So no matter how many dating apps you use, if you're looking for a date before Valentine's Day, it may come down to some good genes and an even better serenade.


Torah Kachur

Science Columnist

Torah Kachur has been the syndicated science columnist for CBC Radio One since 2013. Torah received her PhD in molecular genetics from the University of Alberta and studied how worm gonads develop. She now teaches at the University of Alberta as a contract lecturer in cell biology and genetics.