London, Jan 14 (ANI): When it comes to butterflies, sex is not as graceful an affair as one might think, claims a new study, which found that male monarch butterflies decide how much of their own sperm to deposit based on the female's mating history.

To reach the conclusion, Michelle Solensky of The College of Wooster in Ohio paired male monarch butterflies with a selection of females that had had different numbers of partners.

She found that males could selectively increase or decrease the amount of fertile sperm in their deposits. For example, they deposited slightly more into a female for each of her previous mates

The study has been published in the journal Animal Behaviour.

"This may explain earlier observations that the last male to mate has a reproductive advantage," New Scientist quoted Solenksy, as saying.

Later, the researcher arranged for some female butterflies to receive a large deposit from a single male, and others to have a small deposit from three different males adding up to a similar volume.

When males later mated with the females, they used the same amount of sperm irrespective of which experimental group the female butterfly had been in. This showed that the males were adjusting their sperm on the basis of volume - not the number of previous partners.

"I don't know of any other creatures that respond to the amount of sperm inside their mates," Solensky added.

"The new aspect for butterflies is that they can assess the intensity of sperm competition without ever witnessing previous matings," says Simone Immler at the University of Sussex in the UK.

Since monarch butterflies don't use chemical signals like pheromones, Solensky suspects that sensors on the male penis detect the volume directly, like the dipstick in a car's oil tank.

If so, the cells that lack nuclei may act to bump up the volume of the deposit and discourage rivals.

Sensors on the male monarch butterfly's penis may detect the volume of sperm directly, like the dipstick in a car's oil tank. (ANI)