Q: If zebra finches learn their song by imitation, shouldn't there be very little song diversity? And if so, how can the females judge the males' songs if they all sound the same?
Anonymous
A: Wow-that's an excellent question! It seems that zebra finches do not like to have a song that is too similar to that of other males. For example, if five male siblings are tutored by their father, only one or two of them will accurately imitate his song-the rest of the siblings diverge and sing different songs. There is an interesting parallel to this effect in population genetics. It is called evolutionary stable polymorphism: For example, different people have different hair color, and this diversity persists over many generations. If most people find one hair color (e.g., blond) more attractive, how come blond people are not becoming more common in each generation? One mechanism that can preserve polymorphism is called "frequency dependent selection," for example, blond hair is not considered as attractive in Scandinavia, where it is very common. Back to songs, polymorphism of songs in a group might be a result of frequency dependent imitation (young birds selecting some rare sounds from their tutors) or frequency dependent sexual selection (females preferring songs with some rare qualities, while some juveniles prefer to imitate their fathers).
Keep asking questions,
Ofer
From NOVA's website
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