Why male flies favour longer copulation times

Washington, June 12 (ANI): A study on flies of the species Drosophila montana has shown that females engaged in extended intercourse wait longer before they mate again, increasing the first fly's chances of fathering offspring.

Published in the open access journal BMC Evolutionary Biology, the study explains why males favour longer copulation times.

"By inducing a mating delay in the female, the persistent male extends the time over which his sperm is exclusively used to sire progeny, and reduces the likelihood of the female being re-inseminated by a competitor," write the researcher behind the study.

Lead researchers Dominique Mazzi from the University of Jyvaskyla, Finland, now at ETH Zurich, Switzerland, and Kirsten Klappert from the University of St Andrews, UK, now at EAWAG/ETH Duebendorf, Switzerland, point out that male and female flies of the species Drosophila montana seem to struggle for control over the duration of copulation.

Once a female has allowed a courting male to mount, and after an initial phase of apparent harmony, copulating pairs enter an obvious conflict phase wherein females conspicuously attempt to dislodge the mounting male by vigorously kicking with their hind legs, flicking their wings or attempting to move away.

During the study, the researchers observed that when females were prevented from dislodging the copulating male, matings lasted one-and-a-half times longer than when female movement was unconstrained.

They say that this finding suggests that female resistance normally shortens copulation duration, although the length of the conflict stage indicates that persevering males who hold on gain a significant extension of copulation time.

According to them, protracting copulation in this way does not lead to enhanced insemination, or to increased progeny production from the union concerned.

However, if the scientists interrupted copulation early, and other males were available, the females soon mated with another partner.

Extended copulation correlated with the presence of male competitors, suggesting that the male drive to prolong copulation is spurred by the presence of competitors, and is effective in keeping this competition at bay. (ANI)