The study led by Alireza Fazeli found that the reproductive system of female mammals may 'sense' the presence of sperm and react to it by changing the uterine environment.
The researchers stated that this might be the molecular mechanism behind post-copulatory sexual selection, in which females that have mated with several partners play a role in determining which sperm fertilizes their egg.
They reported the first chemical evidence of a sperm recognition system in the oviducts of pigs, standard animals for such research because their reproductive systems are similar to humans.
With post-copulatory sexual selection, the female is in control, her oviducts selecting the 'winner', the best quality sperm from the healthiest male, and rejecting the rest.
"This study clearly shows that the sperm's arrival in the female reproductive tract triggers a cascade of changes that leads to alteration of protein production in the oviduct and a change in the oviductal environment," Fazeli said.
"We speculate that this is mainly done to prepare oviduct environment for storing sperm, fertilization and early embryonic development," he said.
"We know sperm selection exists in nature, especially in promiscuous species, when females mate with several males.
"Baboons are a good example. During one reproductive cycle, if the female mates with several males, most of the time the offspring belong to one of the males — not a spread between all of them... We are now seeing what can be the molecular basis for this effect," he added.
In the study, the researchers compared protein changes in the oviductal fluids before and after sperm introduction to the reproductive tract.
The data showed that the mammalian female reproductive tract was a far more tightly regulated environment than once thought.
Fazeli contemplates that the finding would have profound implications for the massive IVF industry.
He added that the deep new molecular insights into this post-coital "ladies' choice" has profound implications for in-vitro fertilization (IVF), cloning, and animal breeding.
The study will be published in Journal of Proteome Research.