Imagine, you are in a white room and it is quiet. And there is this guy with you and he is frantically running around you while he is strangely quiet. He is freaking you out, you want him to leave. But then you start to hear singing. It seems to come from this guy and it sounds beautiful. Someone who can sing that beautifully, can’t be that bad. Actually he is kind of cute in his frantic way. So you allow him to get closer, you allow him to touch you and end up having sex with him. It is a bit odd that he continues singing all along, but you don’t mind, you like his song.
This is the actual setting that a female fly finds herself in when I am doing my experiments. She is locked in a white room, which we call courtship chamber, together with a muted male, that she finds unattractive as she runs away from him and kicks him when he comes too close. And then, at one point, I start playing back fly courtship song to them and the female’s behaviour changes. She slows down and allows the male to come close and finally copulates with him. However, females are picky, and do not copulate to any song, no, it needs to be the right one.
And I find that the right song needs to have the right song amplitude structure, that is the right way to vary in volume. In specific females like song amplitude structure typical for their own species, which you can see from these data that show what percentage of females copulate to their own species song and to a different species song:
Strikingly females from both species, copulate more when hearing a song with their own species song amplitude structure, however they don’t like song with another species song amplitude structure. Actually the song is rendered as unattractive as silence, which when you think back to the beginning of this post must be really unattractive.