Biology Reference
In-Depth Information
Fig. 14.17
The fruit fly
Drosophila
subobscura
. Photo
© Stephen Dalton/
naturepl.com.
population when relatedness was relatively high, but increased in frequency when
relatedness was lower (Fig. 14.16b).
Courtship and receptivity in fruit flies
A common interest between signallers does not have to rely upon genetic relatedness.
John Maynard Smith (1956) provided a clear and simple example of this in the fruit
fly
Drosophila subobscura
(Fig. 14.17). Males of this species are incredibly enthusiastic
about mating, and will even attempt to mate with lumps of wax about the size of a
fly if they are moved in appropriate manner. When placed with an actual female, a
male will perform a courtship dance in front of her for up to an hour, occasionally
tapping her with his front legs, even if the female rejects him. However, if a male is
placed with a mated female, she will extrude her ovipositor and bend her abdomen
towards him, which causes him to cease his courtship immediately. The reason for
this appears to be that, in this species, forced copulation is impossible and females
never mate multiply. The female wants to signal to the male that she is already mated,
because she does not want to be harassed by a male. The male wants to know when
the female is mated, so that he doesn't waste time trying to court here. Consequently,
both partners have a shared interest in the female signalling when she has already
been mated.
If females only
mate once, then
females and
males have a
common interest
in females
honestly
signalling when
they have mated
Food calls
Another potential example of signalling with a common interest between non-relatives
is provided by the vocalizations made by individuals who have found a source of food.
