Human eggs make their own 'choices', prefer some men's sperm over others: Study
Human eggs make "choices" of their own. They release chemicals that attract sperms from some people more than the others, ultimately deciding which ones succeed in fertilizing them, suggest a new study. These findings could help researchers develop better fertility treatments in the future.
Researchers from Sweden and the UK arrived at these findings after studying samples from 16 couples undergoing fertility treatments. They found that the egg's choice of partner could sometimes be at odds with that of the woman's. "We expected to see some sort of partner effect, but in half of the cases the eggs were attracting more sperm from a random male," John Fitzpatrick at Stockholm University in Sweden, the author of the study, told CNN. "The most likely explanation for this is that these chemical signals allow females to choose males who are more genetically compatible," he added.
Fitzpatrick explained that human eggs release chemicals called chemoattractants, which guide sperms to unfertilized eggs. What we didn't know until this study is those chemicals act differently on sperm from different males. "The idea that eggs are choosing sperm is really novel in human fertility," clinical embryologist Daniel Brison from Manchester University in the UK, said in a statement.
Before mating, humans exchange a variety of chemical signals, from hormones to body odor. In this study, Fitzpatrick and his colleagues were interested in studying interactions after sex. In other words, they wanted to understand how sperms responded to a women's follicular fluid, which helps support a developing egg. It may contain sperm-attracting chemicals that control the speeds of the sperms. "In some cases, the female's follicular fluid is going to make one male sperm do the speedy front crawl, and then another male sperm do the backstroke," Fitzpatrick, an assistant professor in the department of zoology at Stockholm University in Sweden, told CNN.
They found that a woman's follicular fluid attracted certain sperms over others. And it appeared to have nothing to do with a woman's choice of partner. What is more, the eggs sought between 18 to 40% more sperm from their preferred males. The process is random and does not appear to follow a pattern, according to the study. But the researchers speculate that eggs may choose to attract sperms that are genetically compatible. The University of Manchester Honorary Professor added: "Research on the way eggs and sperm interact will advance fertility treatments and may eventually help us understand some of the currently 'unexplained' causes of infertility in couples." The researchers do not know why one in three couples face problems conceiving.
Michael Eisenbach from the Weizmann Institute of Science in Rehovot, Israel, who was not involved in the research, pointed out that the study explains the role of follicular fluid -- which nurses a developing egg -- in attracting sperms. In the future, studies should test whether these results also occur in chemicals produced by mature eggs, she told the New Scientist. The study is published in the scientific journal Proceedings of the Royal Society B.