Research at Syracuse University has shed light — literally — on the battle among sperm cells from the time of insemination to fertilization.
In an article published in April's Science magazine, an international weekly science journal, SU biology professors John Belote and Scott Pitnick and research associate Mollie Manier show that war is constantly brewing among sperm cells by using glow-in-the-dark sperm inseminated in female fruit flies.
Taking a gene from a jellyfish that naturally glows green and a gene from a sea coral that glows red, Belote was able to create flies that had glowing green or red sperm. The two colors enabled researchers to identify which sperm was which and what exactly happens to each inside the female.
Even though the fruit fly is the most studied organism in biology, what happens within the female reproductive tracts is “largely a black box,” Manier said.
So the SU researchers’ work helped to uncover some of the mystery.
“It turns out that they are constantly on the move within the female’s specialized sperm-storage organs, and they exhibit surprisingly complex behavior,” said Pitnick, who also is director of SU's Biology graduate program.
They found that not only do the sperm tails move vigorously, the sperm heads do as well. This prevents the first sperm on the scene from being displaced by a later sperm.
“We found that (the movement) was an evolutionary advantage during sperm competition,” Manier said. “The sperm was able to get back into storage and had a better chance of being used.”
Pitnick said that for female fruit flies, promiscuity is more the biological norm than monogamy.
“Once a female is willing to mate with more than one partner, all bets are off," he said.
The professors’ research gives others in the field insight into the intense selection that happens in post-copulation, and it can have significant implications in the fields of reproductive biology, sexual selection and speciation.
The researchers are now doing further experimentation on evolutionary mismatched sperm and female cells. Also, the team is fielding requests for glow-in-the-dark sperm from as far away as England, China and Israel.
“We’ve only just opened the Pandora’s box of sexual selection,” Pitnick said.
Watch videos of the sperm research and get updates from the Pitnick laboratory at pitnicklab.syr.edu.