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Sea slug carries disposable penis: hermaphrodites shed organ after use, then uncoil another.

A bristly hermaphroditic sea slug mates employing a use-it-then-lose-it penis, and carries one or two extras for future use, researchers have discovered.

Some 20 minutes after copulating, the still-stretched-out penis of a Chromodoris reticulata sea slug "just falls off," says evolutionary biologist Ayami Sekizawa of Osaka City University in Japan. The sea slug then cannot mate for a matter of hours. But when researchers waited 24 hours to offer the slug a second partner, a backup organ segment appeared in place of the discard, she and her colleagues report February 13 in Biology Letters.

"New tissue emerges like lead in a mechanical pencil," Sekizawa says.

The source turned out to be lengths of penis tissue coiled in reserve below the operative segment, Sekizawa found in studying tissue samples under a microscope. Given a little time between matings, the sea slug can essentially advance the tissue to extend three usable sections before having to replenish the reserves by regrowing the whole structure.

Sekizawa and her colleagues got the first hint of the Chromodoris detachable penis when they noticed a sea slug with a truncated organ during an earlier experiment. Watching 31 matings, the researchers determined that each slug extends its penis into the reproductive tract of the other, with mutual sperm delivery lasting nine minutes on average. As the slugs disengage, they each crawl around, penis extended. Finally the penis, with no preliminary shrinking or pinching inward, simply detaches.

Several evolutionary paths could lead to detachable penises, says evolutionary ecologist Nico Michiels of the University of Tubingen in Germany. In many species, a male plugs the female reproductive tract and stymies a rival, Michiels says. An abandoned penis could certainly serve as a plug.

Also, a left-behind penis could autonomously inject sperm after the donor flees the dangers or constraints of more intimate mating. "Not as wild as it sounds," Michiels says. "Male bees have their whole male copulatory system ripped out during copulation, and it continues to pump sperm into the queen even after the male has gone to die."


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Author:Milius, Susan
Publication:Science News
Geographic Code:9JAPA
Date:Mar 23, 2013
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