Presence of females makes sperm quicker

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What makes guppy sperm swim faster? The presence of females, according to research by scientists from Argentina and Italy published in a recent issue of the journal Biology Letters.

Clelia Gasparini, Alfredo Peretti and Andrea Pilastro stripped 46 male guppies of all sperm before being randomly allocated to one of two treatments simulating different levels of mating opportunities (constant visual contact with three females or female deprived).

After three days of treatment, the males were stripped again and sperm velocity was assayed with a computer system.  

The authors found that the sperm in males that were in visual contact with females swam significantly faster than in those that were deprived of such contact.  

The results suggest that male guppies adjust sperm velocity according to the availability of potential mates.  

As sperm velocity has been shown to be a significant predictor of sperm competition success, increasing sperm velocity may help increase the number of successful matings for the males.

For more information, see the paper: Gasparini, C, AV Peretti and A Pilastro (2009) Female presence influences sperm velocity in the guppy. Biology Letters 5, pp. 792–794.