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For spiders, sex play has its pluses: mock-mating seems to yield later benefits for young arachnids.

When pairs of young comb-footed spiders engage in an arachnid version of heavy petting, the males gain experience that appears to pay off later.

A male spider that repeatedly courts and mock-mates with a not-quite-mature female ends up reaping benefits later, Jonathan Pruitt of the University of California, Davis said January 4. Pruitt proposed that such seemingly pointless spider encounters, which can't produce offspring, may function much like other young animals' racing and wrestling by providing practice for life's future tasks.

"I thought it would sound silly if I called my talk 'Spider Sex Play,'" Pruitt said, "but that's essentially what it is." He ranked it as the first example of any kind of play behavior demonstrated in spiders.

Among Anelosimus studiosus spiders, which live and spin webs by rivers and under bridges from Maine to Patagonia, females don't develop an opening to their reproductive tract until their final molt. Males mature faster and hang around not-quite-mature females, often practicing most of the mating routine.

During almost-sex, the male doesn't load his sex organs with sperm but performs a courtship display by drumming the female's web with his legs and sex organs. If she assumes a cooperative posture, he approximates a mating position too. He then taps her body where the reproductive tract will eventually open.

Sexual behavior even at this stage brings some risks, such as a chance that the male spider will be killed by the potentially cannibalistic female. So sex that can't produce offspring is puzzling. To test the idea that such encounters might be more than wishful mistakes, Pruitt and Susan Riechert of the University of Tennessee, Knoxville set up some young spider pairs for near-matings, but kept other maturing individuals isolated.

After the spiders developed, the scientists observed real matings. If either spider partner had participated at least once in mock sex, a pair tended to reach the point of real mating faster than inexperienced spiders did. Speed should benefit the male by reducing the opportunity for an intruder to displace him. Timing matters because the first male will father most of the eggs in an egg case.

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Author:Milius, Susan
Publication:Science News
Geographic Code:1USA
Date:Jan 29, 2011
Words:353
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