Glowing sperm go head to head in fight to be the daddy


(Image: Syracuse University Arts & Sciences)


Inside this fruit fly reproductive tract, a battle is taking place – a battle of sperm. In turquoise are the sperm of Drosophila simulans; in orangey-red are those of the closely related Drosophila mauritiana.


John Belote of Syracuse University in New York and colleagues took this incredible snap to begin unravelling the secrets of post-sex sperm competition.


Females of promiscuous species – like the fly pictured here and many others, including our own – often mate with more than one male. As a result, the ejaculate of different males mix in the reproductive tract and the sperm cells compete to fertilise the female. But she doesn't leave it up to them alone. She can exercise what's known as cryptic female choice, giving some sperm an advantage over others.


The idea that animals compete for mates is commonplace, but we are only now beginning to understand post-sex competition and its influence on evolution.


Understandably, it's difficult to observe the rivalry taking place inside the female body, and even recognising the sperm from different males is tricky. By making sperm glow in the dark, the researchers gave themselves a front-row seat to watch the sperm battle and also the chance to see cryptic female choice in action – for example, the female ejecting sperm from her reproductive tract.


Journal reference: Current Biology, DOI: 10.1016/j.cub.2013.07.086


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