A new piece of research on red junglefowl, an ancestor of chickens, has shown that males can adjust the speed and effectiveness of their sperm, based on whether they find their mate attractive.
Published in the Proceedings of the Royal Society B, the study adds to the growing body of evidence that males from promiscuous species, including humans, increase the chances of fertilization when the female is deemed to be attractive.
"Female attractiveness is determined by the expression of a sexual ornament - the comb - which is phenotypically and genetically correlated to the number and mass of eggs females lay," ABC Science quoted co-authors Dr. Charlie Cornwallis, of the University of Oxford, and Dr Emily O'Connor, of the Royal Veterinary College, as saying.
For their study, the researchers collected natural ejaculates from dominate and subordinate red junglefowl males housed at the University of Stockholm.
They reveal that the males had either just mated with attractive or unattractive females.
The researchers later separated the sperm from the seminal fluid, and analyzed the quantity and characteristics of both.
"There was a strong relationship between sperm velocity and the volume of the ejaculate sperm came from," write Cornwallis and O'Connor, adding that males allocated "larger ejaculates to attractive females".
Although the researchers have yet to unravel the mystery behind it, they have an have an intriguing theory.
"Males may alter the velocity of sperm they allocate to copulations by strategically firing their left and right ejaculatory ducts, which can operate independently," they say.
Thus, according to them, stimulation from sexy, attractive females leads to the double firing.
"Furthermore, differential firing of left and right ejaculatory ducts may contribute to how males strategically change the number of sperm in their ejaculates, a phenomenon that is widespread, but for which the mechanism remains unknown," they say.
The researchers now hope that future studies will better identify how males adjust the sperm and seminal fluid in their ejaculates, and how this affects fertility rates.