Sometimes babies come along at inopportune times - after sex, the human body can only delay fertilization for 3 to 5 days. But what if each woman had her own personal sperm bank? What if she could hold on to sperm until she felt ready to get pregnant?
Researchers have found many females in the natural world possess the nifty ability to store sperm within their bodies for weeks and even years. In the past decade, scientists have discovered that female birds, reptiles, insects, and even whale sharks use this uncanny reproductive method. By keeping the sperm on hold, researchers say, a female can start pregnancy at her leisure.
One of the most extreme examples of this trait exists in queen ants. They can fertilize their eggs with sperm stored for up to 30 years.
But how these sneaky females pull it off?
Dr. Klaus Reinhardt from the University of Sheffield has a new study, published in Proceedings of the Royal Society B, which found that female crickets are able to store sperm within by slowing the sperm's aging process to prolong its viability.
By analyzing sperm taken from female crickets' reproductive tracts, Reinhardt and his team monitored the metabolic rate of male crickets' sperm and how many 'free radicals' it produced - measures of the sperm's aging process. The scientists found that both the metabolic rate and the level of free radicals of stored sperm were much lower than that of un-stored sperm. By dampening the aging process, females can keep sperm alive almost indefinitely.
Not interested in cricket sex? Dr. Reinhardt pointed to a practical application of this finding, saying it suggests that commonly used semen analysis tests may not accurately gauge whether a man is able to father children.
"Infertility tests on sperm are notoriously unreliable, and this could be one reason why," Dr. Reinhardt said in a written statement. "Females could be manipulating sperm."