Inside every Drosophila melanogaster (fruit fly) female is a battleground where sperm can jockey with each other for the honor of fertilizing her eggs. By sequentially mating females with males genetically-engineered to produce sperm that glow either green or red (see video below), scientists have been able to directly observe sperm from two different males competing in what resembles a fruit fly version of Tron. Color coding the sperm in this way allows researchers to distinguish one male’s sperm from another’s and determine who the winners are.
“Sperm from two different males genetically-engineered to express either green or red fluorescent proteins compete within the female reproductive tract of the fruit fly Drosophila melanogaster.”
Surprisingly, it’s not always the fastest sperm that wins.