Prof Mala Murthy, Princeton
Mala Murthy has been studying a species of fruit fly called, Drosophila Virilis, where the two sexes sing to each other during courtship. She’s trying to understand neurologically what underpins their courtship ritual, and ultimately, how we humans also harmonize. She explains to Chris Smith...
Mala - The male and female of this particular species, Drosophila Virilis, have an interesting courtship behavior where while the male is singing to the female, and she’s singing back to him, he’s constantly interacting with her in a kind of salacious way. He’s licking her genetalia with his mouth parts and he’s rubbing his front legs against her abdomen. And what we found is that the timing of these two contact behaviors, the licking of her genetalia and the touching of her abdomen, they’re precisely timed with her song. And that she’s actually using this information in combination with his song to determine how much song she produces and when she produces that song in relation to him.
Chris - Is this mediated or generated at the level of higher centers in the nervous system, or is there some kind of central pattern generator which is integrating the input from the male – the touching and the licking – with the sounds. So, that then that triggers the correct output at the correct time of her own song.
Mala - That’s exactly right that there’s this sort of integration going on. But interestingly, the tactile inputs – the licking and the rubbing – are coming from her abdomen, and the auditory inputs are coming from her antenna, which are on the head. And so, the auditory information comes in via the brain, whereas, we found that the tactile information comes in directly to her ventral nerve cord, which is the fly’s equivalent of its spinal cord. And so, somewhere in that spinal cord equivalent, she’s integrating this tactile information with the auditory information from the brain to pattern her song. And so, we think in that part of the nervous system, in this ventral nerve cord, there is this, as you say, a central pattern generation for her that guides the timing and the amount of her song and these pieces of sensory information interact with it.
Chris - Are both necessary? What I’m getting at is if I were to remove the antennae, or remove the input from the antennae and leave just the rubbing or the licking, for example, or I divorced the licking from the antennal detection sound, would I still get the duetting off of the female, or do you need all of those inputs to sync up in order to get the output?
Mala - The experiments we did are just as you described. We remove each of these sources of sensory information and ask what happens to the behavior. And we found that the tactile information, the rubbing and the licking, is the most important for song timing but the auditory information sculpts how much song she produces, and so, therefore, also end up being critical for the duet. And so, both of these sensory cues play a role, although they’re sort of biased towards the tactile information, she relies more heavily on that and that’s really novel. I think most studies of duetting have focused exclusively on acoustic interactions which makes sense, you know, that ultimately the behavior is about the two acoustic signals from these two animals and how they interact. But what we found is this role for a non-acoustic signal in timing the duet and I think that will be important to consider going forward.
Chris - Flipping it around, how does the male coordinate all of that? Is it the same system just running in reverse, so what would be the pattern generator receiving inputs in the female is the same circuitry but it’s running backwards and just generating an appropriately synced up output in the male which is then, obviously, supplied to the female.
Mala - The songs the male and female produce are different. They have different timings and they’re recognizably different. And the males are actually capable of producing female-like songs. So, it’s as if they have two circuits – one to generate a male-like song with male timing and the other to generate a female-like song. And the only way we can get the males to produce these female-like songs is if we paired them with another male and these males then received the courtship licking and rubbing, and the acoustic input, the auditory input from the other male. And when he got those pieces of sensory information combined, just as the female normally does, it then drove this other circuit to produce the female-like song. So, it’s as if the males have sort of both, sitting there within the nervous system and they choose which one to trigger based on the sensory information they receive.