'Glow-in-the-dark' Sperm Reveal Sexy Secrets

This is the reproductive tract (less ovaries) of female D. melanogaster initially mated to GFP-sperm male then remated to RFP-sperm male. Green sperm heads have left the storage organs and can be seen mixing with red sperm heads in the bursa. (Credit: Scott Pitnick, Syracuse University)Creative thinking inspired Syracuse University biology professors to genetically alter the heads of fruitflies to be green or red. Because most of nature is promiscuous, meaning that the female mates with more than one male, in search for the best sperm for her offspring — it’s been very difficult for researchers to keep track of events within her body.

Besides the female practicing her own Darwinian supreme sperm selection, rival sperm are competing to fertilize her eggs. We know that these rival sperm will even form teams, supporting their guy’s sperm, much like a hockey team bands together for victory.

By quantifying sperm movement and fate within females inseminated by a green-sperm male and a red-sperm male (including real-time analyses of sperm motility in vivo), the researchers were able to unambiguously discriminate among hypothesized mechanisms underlying sperm precedence.

“Despite nearly a century of intensive and innovative work on the reproductive biology of the fruit fly [Drosophila melanogaster], much of what we know about the female reproductive tract is a mystery,” continues team member Scott Pitnick. “Our jaws hit the floor the first time we looked through a microscope and saw these glowing sperm. It turns out that they are constantly on the move within the female’s specialized sperm-storage organs and exhibit surprisingly complex behavior.”

Pitnick says his team has created similar glowing sperm populations for other species, including ones that hybridize, so he can observe what happens when sperm and the female are evolutionarily mismatched. “I suspect we have just scratched the surface of using this material,” he says. via Science Daily