Size 'doesn't matter for sperm'

25 November 2008 01:25am

Size does not matter when it comes to sperm, according to a new study.

Research detailed in the journal BMC Evolutionary Biology casts doubt on the common assertion that sperm with longer tails can swim faster.

The speed at which a sperm swims is a key factor in its capability to fertilise an egg.

While increased tail length does mean more thrust, this can be cancelled out by the drag caused by a correspondingly larger head.

The proportions of the sperm are the key factor, the researchers found.

Stuart Humphries, from the University of Sheffield, took part in the study with collaborators from the University of Western Australia.

He said: "It seems clear that some assumptions regarding the physics of sperm locomotion have hampered our progress in understanding the processes mediating sperm competition.

"It is commonly believed that selection for increased sperm performance will favour the evolution of longer, and therefore faster swimming, sperm. In fact, the relative lengths of a sperm's constituent parts, rather than their absolute lengths, are likely to be the target of selection."

The authors said that taking account of liquid dynamics could see research in this area progress rapidly in the future.

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