Tarantula (side view). Photo by Senta Niederegger.
Posted on 09/27/2006 7:16:29 PM PDT by PatrickHenry
Discovery could have implications for evolutionary origin of spider silk
Researchers have found for the first time that tarantulas can produce silk from their feet as well as their spinnerets, a discovery with profound implications for why spiders began to spin silk in the first place.
Adam Summers, a UC Irvine assistant professor of ecology and evolutionary biology, was among the team of scientists who made the discovery using zebra tarantulas from Costa Rica. The team found that the tarantulas secrete silk from spigots on their legs, allowing them to better cling to surfaces. Until now, spiders were only known to spin silk from spinnerets located on their abdomen and to use the silk to form webs for protection and capturing prey rather than for locomotion.
The findings are published in the current issue of Nature.
“If we find that other spiders in addition to these tarantulas have the ability to secrete silk from their feet, this could represent a major change in our evolutionary hypothesis regarding spider silk,” Summers said. “It could mean that silk production actually originated in the feet to increase traction, with the diversity of spinneret silk evolving later.”
The researchers placed tarantulas on a vertical glass surface. Though ground dwelling, these spiders can normally hang on to vertical surfaces by using thousands of spatulate hairs and small claws. However, the scientists noticed that when the spider started to slip down the surface, it produced silk from all four pairs of legs, allowing it to adhere to the glass for more than 20 minutes. The silk secretions were clearly visible on the glass. Using scanning electron microscopy, the scientists also were able to see the openings on the legs that resemble the silk-producing spigots on spider abdominal spinnerets.
The next step, according to Summers, is to investigate whether the silk produced by the feet is the same as that produced by the spinneret. Many spiders can produce seven different kinds of silk. Scientists will look at the genes involved in silk production from the feet, compare them to the gene family that leads to spinneret silk production, and be able to better determine whether silk was originally used for traction, or whether that was a secondary usage that came later.
Collaborating on the study were Stanislav Gorb of the Max Planck Institute for Metals Research in Germany; Senta Niederegger of the Friedrich Schiller University of Jena in Germany; Cheryl Hayashi of UC Riverside; Walter Votsch of the Max Planck Institute for Developmental Biology in Germany; and Paul Walther of the University of Ulm in Germany.
ROFLMAO!!! The girls I grew up with weren't afraid of them. Country girls rule!!
It's only a university press release about a forthcoming article in Nature. So why not dump it into "Chat"?
***stares at feet and sighs***
A legitimate science article moved to Chat that quickly?
That's disgraceful! FR used to be more accommodating to science.
Oh no! I wasn't saying that at all. They are already dead.....
PH, you think locomotion is evolutionarily more important than foraging? I would think that the use of silk to create webs that can catch prey would be a more important evolutionary event; the use of silk as a means of locomotion being a next step to better situate the means of ambush, not the other way around. This can actually be supported by the fact that some species of spider create ground traps with silk rather than create webs that are arial.
What's more "important" is not necessarily the function that evolves first. What's "easiest" is often the first thing to evolve (i.e. involves the least amount of modification of existing structures or biochemistry).
Evolution usually proceeds by small stepwise modifications, and the first few small steps towards the development of modern silk and silk usage may not have involved the catching or holding of prey, because that would involve stronger silk and more complicated usage of it than one would expect during the earliest stages of silk production.
However, it wouldn't take much modification of existing insect physiology for an early insect to have had a viscous substance (a proto-silk, as it were) seep out of its feet in order to improve traction as it walked (rather in the way that snails and slugs currently leave slime trails). If that was the first step (no pun intended), from there evolution would have driven the stepwise improvement of the sticky substance itself, its applications, the behaviors which drove how it was used, etc., until much later it was suitable for creating "suspension bridges", traps, wrappers, etc.
Oh, and speaking of caterpillars, while moth caterpillars often spin protective cocoons to shield themselves while they pupate, butterfly caterpillars don't, they just lay a very sparse (almost invisible) layer of silk as they walk across leaves and twigs, in order to improve traction and lower the odds of falling off, and also make tiny "pads" of silk to anchor their "tails" when moulting their skins (including one to anchor themselves as they moult their last larval skin and pupate).
So in butterflies, at least, silk production is still used solely for "attachment" purposes, if that helps shed some light on this issue.
Even if catching prey is more important than locomotion, that doesn't answer the question of which came first. Evolution doesn't give creatures what they "need most". It just works with whatever happened to be there. Let's suppose there was some sort of scent gland in the feet of the ancestral spider; it might have been a small modification to turn that into a sticky foot adhesive, but it would take many modifications to turn that into the abdominal wonder gadget spiders have today.
It's possible that the fossil record might someday tell us what came first. A better route might be to look at the genes, and see where the foot-spinneret fits into the cladogram of arachnid abdomen-spinnerets. If the foot-spinneret came first, it will be genetically equidistant from the abdomen-spinnerets of all spiders, because all abdomen-spinnerets will be modifications of some close version of its gene(s). If the foot-spinneret came second, then its gene(s) will be closely related to the abdomen-spinneret gene(s) of the tarantulas.
Pretty complicated, actually, compared to what would be necessary for primitive silk production from simple pores on the feet. Again, compare the intricate production of a modern orb web (which involves multiple different kinds of silk, as well as precision start/stop control and fancy "architecture") with, say, a slug's slime trail.
In addition, most insects that spin silk or other viscous substances similar to silk do so from abdominal sources. Would this not indicate that this was the originally evolved method and not from the legs?
Maybe, maybe not. If all the "abdominal spinners" are members of a monophyletic group relative to a more polyphyletic grouping of "foot (or other non-abdominal) spinners (i.e., if abdominal spinners all share a more recent common ancestor than all silk spinners of any type), then this would indicate that a) abdominal spinning evolved once, b) all modern abdominal spinners descended from the first one, and c) non-abdominal spinning evolved even earlier than abdominal spinning and abdominal spinning likely evolved as a special case of a more generalized spining ability).
The relative abundance of abdominal spinning might simply be the result of abdominal spinning being a much more effective strategy, and those insect groups which have it have prospered and diversified more successfully than those silk-spinners which didn't achieve this "breakthrough".
Very interesting. Thank you.
...as of fromage left out of the refrigerateur too long.
Cheers!
...as of fromage left out of the refrigerateur too long.
Cheers!
Hi--
This thread was hijacked to the Chat forum before any contentious posts were made. It was a good science thread, with good, serious comments. But, off to Chat, with the crop circles and other drivel.
Something has changed, and this tells us where science is now relegated to here on FR.
Pretty sad. I'm not sure how much longer I can put up with this.
Its like, science--take a hike, we're not interested.
Maybe the unwanted comments [note: "irreverent" for a religious topic, how about the word "dysgnostic" for 'interfering with the seeking of knowledge'] come about because people see it on a Chat thread.
All kinds of threads get hijacked to some extent.
Another possibility is that the jokes and whatnot are defensive--people feel the are not up to an informed comment, but they still want to participate.
Cheers!
There, all fixed!
That part sounds a bit hazy on the details, Ich. Kind of hand-waving.
Begin segue.
Speaking of hand-waving...
End segue.
Are there any species of spiders or closely related critters who "spin a web" and then lasso or similarly throw it over their prey? Might be a nice transitional between leg-silk and posterior silk.
Cheers!
If there was a separate Science Forum, hidden away out back by the Smokey Backroom it would be a disaster.
There are a lot of breaking news stories in science, and they are important; they deserve to be in the News section.
If they were hidden way out back, it would be a victory for the science-deniers who flock to every science thread they can to, well--deny anything that contradicts their religious beliefs. Hijacking these threads has become a passion for them, and any science thread booted out of News is a victory for them.
Pathetic.
I saw something remarkable at a motel once. It was spring, and there were tons of bugs flying around. It looked like one bug was flying very slowly up towards the roof.
It was stuck to a line of silk, like a fishing line. There was about six or seven of these long loose silk threads hanging down to where the bugs were flying (which was right near a light).
The spiders were steelheading!!
I knew for sure it wasn't an accident when a second bug got stuck in a line and whatever kind of spider was up there started hauling it up.
Sometimes, I wonder why I even bother to log in to FR anymore. See something of scientific interest, and before you know it, BANG, it's off to never-never-land with the thread. FR used to be interesting. Not anymore.
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