THE Casanovas of the fruit fly world pay a high price for their sexual
exploits: they die young. Biologists knew that philandering reduces the lifespan
of male flies, but not why. New findings indicate that courting rather than sex
itself is the real danger.
Linda Partridge of University College London and R眉diger Cordts of Ruhr
University in Bochum decided to disentangle the different elements of fly sexual
encounters to see which costs males most. By using mutant males that could not
produce sperm and females whose reproductive tracts had been cauterised so they
could not mate, the researchers created six experimental groups of flies.
Males that could not produce sperm were placed in vials with six other males,
with six females who could not have sex, or with three virgin females and three
cauterised females. The same groups were set up for normal males, and the
researchers then waited for the male flies to die.
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In both groups where males shacked up with males, there were very few
attempts at courtship and no attempted matings at all. The males housed with
cauterised females courted furiously鈥攙ibrating their wings to produce a
courtship 鈥渟ong鈥� and attempting to mount the females鈥攂ut alas, there was
no sex. In the other two groups, the males courted and had sex鈥攂ut only
the nonmutant males produced sperm.
A typical male fruit fly lives for a little more than a month. The males
which had courted females, however, died more than a week earlier than those
with male housemates. And the flies who had sex lived just as long as the
frustrated wooers (Animal Behaviour, vol 52, p 269). This suggests that
courtship, rather than mating, is the main cause of the early deaths found in
previous experiments. 鈥淚 was a bit surprised,鈥� says Partridge.
Even more surprisingly, the normal males that were able to have sex lived
longer than those that courted but did not mate. 鈥淭his may be an artefact,鈥�
cautions Partridge. 鈥淏ut making sperm and mating certainly isn鈥檛 costly.鈥�
Partridge believes that male flies which do not pursue females live longer
simply because they take life easy, spending more of their time sitting still.
The courting flies were 鈥渦sing up a lot of fat rushing around鈥�, says Partridge,
who thinks that an elevated metabolic rate causes early death.