Saturday, February 25, 2012

Male Spider Amputation

Spider with black pedipalps- Wikipedia
Spider sex is a dangerous game.  All spiders are predatory, and many eat other spiders including their own kin.  The infamous Black Widow and many other species may respond to a male's sexual overtures by over powering and eating him, which gives a whole new meaning to a "dinner date."

Spiders have a pair of structures behind the mouth called palps.   Male spider's palps are specialized into sexual organs.  They use these palps to transfer and store sperm from its gonads.  Once one successfully "hooks up" with a female, the male inserts his palp into her sexual organ to transfer the sperm.

You would think that having survived the courtship approach to the female, life would be good.  For some orb spiders, when the male withdraws or is pushed away, the palp amputates and remains in the female.  The hard hearted female in some cases may then dine on her mate.

Insects, like other animals live to reproduce their own progeny.  Like humans, the females can be sure that the young are their own genetic stock, the males, not so much.  Some species like the walking sticks hang on in prolonged intercourse to prevent other males from adding their sperm to the mix.  Others seal the female opening after introducing their sperm to prevent further mating.  This would seem to be a possible reason for the detached palp.

A new study in shows that for at least one variety of orb spider, there is more to this event.  Researchers studied the orb-web spider Nephilengys malabarensis which has detachable genitals.  They studied 25 pairings under controlled conditions.  In 88%, the male's palp was detached and remained in the female.

Now is where it gets really kinky.  The scientists observed the females with the detached palp in place for various periods of time up to 20 minutes.  Then, as Dave Barry says, "and I am not making this up," they removed the palp and counted the remaining sperm.  What the female thought about the observation or the removal was not recorded.

They found that 30% of the sperm were transferred before the palp was broken off.  If it remained in place for 20 minutes, 85% of the sperm were transferred.  In other words, like the old Timex commercials said, the palp "keeps on ticking."

Not only does this allow for a 200% increase in sperm donation, but in many cases the surviving male becomes more aggressive and guards the female against other males, increasing his chance of posthumous fatherhood.  Meanwhile, in a laboratory setting it took the female seven hours to get the palp out on her own.

In addition to other spiders, male scorpions, fire ants, ground beetles and cephalopods are known to amputate their genitals.  I assume that scientists in the future will be watching for more "breaking news."

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