By Susan Milius
When nematodes have sex with the wrong species, sperm can turn into rampaging killers.
In the worst mixed-up couplings between tiny, eyeless worms of the genus Caenorhabditis, the sperm of males from more sexually competitive species can be so aggressive they reduce the fertility of, or eventually kill, the receiving partner. The marauding sperm push beyond normal receptacles for sperm and storm into ovaries and the rest of the partner’s reproductive tract, says Eric Haag of the University of Maryland, College Park.