What happens when sperm from two different males meet up? Is there all-out war, or do they live in harmony? Females in many animal groups have multiple mates - often close enough together in time to cause the sperm to mix. While no battle-axes are visible, a known phenomenon is that the sperm from the second mate almost always triumphs, somehow disabling the first mate?s sperm. Just how does it manage this feat?
In a report in the 29 July issue of Nature, Jerry Coyne and colleagues from the University of Chicago, Illinois,show that fruitflies (Drosophila melanogaster) have two different weapons - displacement and incapacitation - to disable the sperm of the first mate. In displacement the incoming sperm physically push the sperm of the first mate out of a receptacle in the female where it is stored. Incapacitation is slightly different because it does not even require the sperm of the second mate. Instead, something in the seminal fluid destroys the ability of the first sperm to perform its duty of fertilising eggs.
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