The Evolving Behavior

My following comments are in regards to an article found in, Science News v. 165, 4/24/04, p. 269.

"Male Spiders Amputate Organs, Run Faster" is about a species in which "The male spider grows to only about one-hundredth the size of a female, yet one pedipalp accounts for some 10 percent of his body mass."

The pedipalps are leg-like limbs on the front of the spider and are used for delivering sperm to the female. Larger pedipalps, more sperm, more reproductive success. However, two of them seem to be a bit too much for this tiny variety, slowing them down. Yet pedipalps naturally grow in pairs just like all the other limbs.

What's the male Tidarren sisyphoides spider to do? One researcher "rates the spiders as an 'extreme example' of a species that 'got stuck in a massive evolutionary conflict and had to evolve a behavior to get out.' "

Can't you just see the little guys scratching their cephalothorax, trying to figure out a way to evolve a solution? And what, you may be wondering (if you haven't heard or don't remember) is the way out that just happened to evolve? A mutation that caused one pedipalp to fall off early? Oh wait, that guy said something about a behavior... could it be something more complex? Oh yes, indeed.

According to a report in the, April 6 Proceedings of the National Academy of Sciences, "within hours after a young males penultimate [why can't they just say "next to last"?] molt prior to mating, he amputates one of his pedipalps." They're telling us spiders evolved the behavior of removing a limb? What, do they just chew it off? No, "He does this by attaching a strand of web silk to one pedipalp, tightens the silk thread by turning in circles, and then pushing at the pedipalp with his legs."

Sort of reminds me of pulling a loose tooth with a string. How could such a behavior evolve? What sort of mutations or other inheritable change (they certainly don't teach such things in little spider school) could have given spiders the programming for such otherwise bizarre and self-destructive behavior? Looks like another case of sheer faith in "it just happened" evolution.


Until Next Time,
David Bump