Researcher shows how cone snails developed poison gland from spare gut parts
May 20, 2011 by Bob Yirka
Conus geographicus (a marine snail) Credit: Kerry Matz/National Institute of General Medical Services
(PhysOrg.com) -- Canadian Louise Page, associate professor at the University of Victoria, BC, has solved a mystery that has perplexed zoologists since early 19th century naturalists first wondered if venomous cone snails might have developed their poison producing glands through evolution of their esophagus somehow; speculation that of course led many to wonder if that were so, how did the snail continue with swallowing and digesting its food.
Cones as they are known colloquially, are a genus of snails that use a small tube to shoot harpoon-like teeth connected to a radula (a spaghetti like string) through a proboscis at suspecting prey to stun or kill it; they then haul their prey back to them and devour it, spitting out the parts they dont like. The snail can turn and point the proboscis (which looks sort of like a cartoon version of a tiny elephants trunk) at its prey and after loading a tooth with poison launch its "harpoon" by forcefully contracting muscles, situated at the base of the proboscis. Some estimates put the number of different species of cone snails in the neighborhood of six hundred or so, of varying sizes and coloring; though most are pretty little, some can grow to as long as 23 centimeters (about nine inches) and pack sufficient punch to kill a human being.
Page found the answer in Hawaii, home of the cone snail species Conus lividus, where, as she describes in her paper in Proceedings of the Royal Society B, she grabbed a mass of eggs, took them back to her lab and set about hatching and raising them. Along the way she singled out specimens during different stages of their development (when they were still larvae) fixed them with chemicals and sliced them up and photographed them to see what was going on. She then fed the whole batch of photos into a computer program that allowed her to watch as the larvae developed, and was then able to see that the cone snail originally has two sets of digestive tracts, one of which develops into the venom gland. Mystery solved.
Page explains that the process is known as modular evolution, whereby a species develops a trait over time without disrupting other important bodily functions, something that has been seen in a wide range of other animals and insects.
More information: Developmental modularity and phenotypic novelty within a biphasic life cycle: morphogenesis of a cone snail venom gland, Proc. R. Soc. B, Published online before print May 18, 2011, doi: 10.1098/rspb.2011.0501
Abstract
The venom gland of predatory cone snails (Conus spp.), which secretes neurotoxic peptides that rapidly immobilize prey, is a proposed key innovation for facilitating the extraordinary feeding behaviour of these gastropod molluscs. Nevertheless, the unusual morphology of this gland has generated controversy about its evolutionary origin and possible homologues in other gastropods. I cultured feeding larvae of Conus lividus and cut serial histological sections through the developing foregut during larval and metamorphic stages to examine the development of the venom gland. Results support the hypothesis of homology between the venom gland and the mid-oesophageal gland of other gastropods. They also suggest that the mid-region of the gastropod foregut, like the anterior region, is divisible into dorsal and ventral developmental modules that have different morphological, functional and ontogenetic fates. In larvae of C. lividus, the ventral module of the middle foregut transformed into the anatomically novel venom gland of the post-metamorphic stage by rapidly pinching-off from the main dorsal channel of the mid-oesophagus, an epithelial remodelling process that may be similar to other cases where epithelial tubes and vesicles arise from a pre-existing epithelial sheet. The developmental remodelling mechanism could have facilitated an abrupt evolutionary transition to the derived morphology of this important gastropod feeding innovation.
© 2010 PhysOrg.com
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May 20, 2011
Rank: 1 / 5 (2)
PART of the mystery is solved!
WHY did the snail ADAPT to serve its energy needs in this manner. Did things get crowded? SO the venom is defensive as well as aggressive energy grab - like a small firm that is attractive to predatory big ones so it swallows a 'poison pill' that makes it unsavory (after many other firms have been swallowed of course) while using the leverage/debt/poison to aggressively compete in a niche where it is under-sized, perhaps? HOW did it know that it was a meal on another's table. How does a species transmit threat sensitivity across its genome? How does it choose a response or how does the threat trigger a response. I say again, evolution IS adaptive..evolution IS after the fact change. This snail became different to LIVE: Seek the adaptive trigger.
word-to-ya-muthas
May 20, 2011
Rank: 1 / 5 (1)
The only evident parallel I can see, please help me here, is if prey and predator were all in the same, relative environment; warm, saltwater, isolated and something triggered, or forgot to prevent, -gasp- cannabalism -gasp, whereupon we would get both breeding/mating pressure and genome selection AT WARP SPEED! (Like lactrodectus)
Many creatures have failed evolution's test: The need to adapt to a living planet's changes.
word-to-ya-muthas
May 21, 2011
Rank: 3 / 5 (2)
Evolution doesn't have a goal. It's not a conscious entity. The mutations that don't kill the animal before it reproduces are passed on. It's as simple as that.
May 21, 2011
Rank: 1 / 5 (2)
No, your solution/thought IS SIMPLE and I am sure you are comfortable with that, but the dynamism of evolution suggests adaption. Adaptation and the mechanisms of adaptation were my point and you addressed NONE OF THEM...and your solution...simple.
Here: http://www.physor...616.html
and here: http://news.natio...ion.html
"There IS more of heaven and earth than dreamt of in our philosophy" do not purchase, hook, line, and sinker, the notions your textbooks sell you. If they were always correct, there would be no new textbooks!
Reproduction, evolution, and mutation have constraints to their expression IF not, every reproductive act would fail due to unbridled mutation! No, something is guiding them, resisting cascade failure.
word-to-ya-muthas
May 22, 2011
Rank: 4 / 5 (4)
Yes. The environment. Nothing else is needed nor is there any evidence that anything is involved.
Yes. Death. And repair mechanism.
Bullshit. There is no evidence to support that. Most mutations have little or no effect. On average humans are thought to have 3 or 4 mutations each. Most of those have little or no effect.
Word to you - your sig is not funny nor are you logical nor are you using evidence.
And my mother is dead but she had a degree in anthropology.
Ethelred
May 22, 2011
Rank: 1 / 5 (2)
"Yes. Death. And repair mechanism."
Apoptosis -programmed cell death, is turned OFF by cancer cells, it does this every time cancer shows its angry face,..the HeLa line of cancer cells are still around though Henrietta Lacks has been dead for over 40 years. No, death is not a very good constraining factor and the snails show NO sign of having need or use of a repair mechanism. Evolution requires a point or two of localized pressure, a response to a stimulus not just random mutation.
It is intuitive, unbridled mutation would make life itself impossible and I don't have to prove that...to intelligent human beings...ooooh!
"Nothing else is needed nor is there any evidence that anything is involved."
There is something else involved since selected changes are deselected, as shown in the links I included WITHOUT eliminating any other traits as random mutation tends to do...
May 22, 2011
Rank: 1 / 5 (1)
Here is a video of a cone snail: http://video.nati...one.html
This deadly creature is deadly poisonous exceeded only by the awesome box jelly fish, BUT, head a few hundred miles from their largest habitat and you find the same family of jelly fish, same, living in fresh water and COMPLETELY LACKING ANY VENOM OR STINGING MECHANISM. The difference? Environmental pressure, the second group sees NONE of the predatory activity the larger group does...same bird-one don't fly: ADAPTATION right before your eyes...yes..even YOUR eyes.
Evolution is adaptation to a living world that is itself changing, not random guessing at what should be fancy at the next party.
WORD-TO-YA-MUTHAS
May 23, 2011
Rank: 5 / 5 (1)
And what does have to do with the price of peyote in Peru? Nothing. Death of the ORGANISM is what we are talking about.
Yes. So what. SHE is dead and no longer able to reproduce and the cells only reproduce in labs.
Yeah especially if you lie by bringing in laboratory cancers that have nothing to do with the reproduction of organisms except by killing of the organism thus SELECTING Henrieta OUT of the gene pool. Evolution in action.>>
May 23, 2011
Rank: 5 / 5 (2)
I said that. THE ENVIRONMENT does the selecting. That is the pressure and I NEVER claimed selection random. That is a lie you tell.
But we don't have that. We have SELECTION and mutation. And you are the only one claiming that the mutation is unbridled.
No.
No. That is a lie. Selection is the REMOVAL of changes so they are gone and cannot be deselected since DEATH is permanent.>>
May 23, 2011
Rank: 5 / 5 (2)
I never made any such a claim That is a LIE you tell. Selection is NOT random.
False. Mostly they are neutral.
You either need to start THINKING or quit lying. Selection IS NOT BY MUTATION. Selection is BY DEATH to the organism not being able to survive in the environment.
Do know what DEATH is? I know what random is and it is NOT selection. You are either totally pigheaded on this or lying.>>
May 23, 2011
Rank: 5 / 5 (2)
BY DEATH. Which is what I said.
YES. It is due to random mutation followed by selection by the ENVIRONMENT.
That is something you made up. I NEVER SAID ANYTHING REMOTELY LIKE THAT.
So lets go over this again for people, like you, that don't understand.
There is no goal for evolution EXCEPT survival and reproduction. No species knows the future. The environment does not know the future. There is only a process and no goal no thought no planning.>>
May 23, 2011
Rank: 5 / 5 (4)
The mutations are NOT selection and I no clue as the where you go that from. I sure didn't claim it. I gather you got it from another Creationist.
Mutations usually are neutral. Some make changes that kill. That results in SELECTION the ORGANISM OUT of the gene pool. Some mutations merely lower the odds of reproduction and over time they will be selected OUT of the gene pool since they will die out. Some mutations are advantageous, rare but it does happen. Those will improve the odds of reproduction. Indeed that IS what makes them advantageous.>>
May 23, 2011
Rank: 5 / 5 (4)
Mutation produces the raw material of evolution. Selection prunes out the changes that lower the chances of survival.
Which boils down to:
Which is rather sparse but completely accurate.>>
May 23, 2011
Rank: 5 / 5 (2)
Key part.
Which is exactly what can be expected by mutations followed by selection. The phenotype reversed SOMETIMES to SOME DEGREE and an exact reversal of the genes did not occur. This supports me completely and you not at all.
Link two
PHENOTYPE not GENOTYPE. Do you understand the difference? In both cases there really isn't a reversal. There is only evolution to adapt to a changed environment. Similar environment will USUALLY produce similar organisms.
>>
May 23, 2011
Rank: 5 / 5 (2)
So what you said here is true.
The ENVIRONMENT is what guides them. It knows nothing of the future and doesn't care one whit what happens. It only effects the odds of reproduction.
We have found it. Long ago. Darwin and Wallace knew what the trigger was and is. The ENVIRONMENT.
Ethelred
May 23, 2011
Rank: 1 / 5 (3)
Mutation: http://www.readsc...ion.html
My comments R @ Random Mutation bcause controlled or non-random wood B manmade(statistically skewed/unnatural as far as selection of the fit) or extraterrestrial.
HeLa cancer was mentioned because Henrietta Lacks though cancer ridden HAD NINE CHILDREN and died giving birth to number ten: Arguing that she was "selected out" is an obvious error. Cancer occurs in over 200 different types and it IS a mutation -has been around for over 5000 years just counting humanity, dinosaurs even had it and it IS a mutation but not selection (An Asteroid kill).
Random mutation, cannot account for all the varieties of life and form seen in our world nor in the cone snail:Natural DNA recombination meets the definition of a very precise instrument for change as well as normal reproduction. Cancer/death unless it wipes out a species, does not prevent change, nor make it.Fin
May 23, 2011
Rank: 5 / 5 (2)
May 24, 2011
Rank: 5 / 5 (2)
Mutation is random or mostly so. SELECTION is by the environment and not random. You seem to be unable to make the connection and unwilling to stop pretending that there is only mutation in the theory of evolution.
So. Then she may have passed on a rather nasty gene. And some genes for having a lot children which is usually advantageous. Evolution is a process. It has no goal except for survival and that only for reproduction. A gene that causes painful death but increases offspring is going to be selected FOR.
She didn't have any more children did she? So OK I didn't know she had children. Thus she is irrelevant to your point.>>
May 24, 2011
Rank: 5 / 5 (2)
It isn't a mutation in that is inheritable. Only mutations that are inherited can be part of the evolutionary process.
You really don't understand mutation as it pertains to evolution. CANCERS are caused by NEW mutations of somatic cells and not by mutations in the germ cells. The mutations that lead to a propensity to have cancer CAN be passed on but the mutations that sent the SOMATIC cells out of control are NOT passed on and thus cannot contribute to the next generation.
And I sure never claimed it did.>>
May 24, 2011
Rank: 5 / 5 (2)
It isn't precise. Its rather sloppy even after billions of years of evolution. If it wasn't sloppy there wouldn't be cancer or repair mechanisms or errors in copying. Which would lead to extinction by not be able to compete with the species that did evolve by having a sloppier genome.
Nor does it have a lot to do with evolution. It has SOMETHING to do with it. But only in cancers that kill before reproduction.
You really should quit beating around the bush. I know what your point is but you refuse to be explicit. YOU are pushing ID which is not needed to explain anything in evolution. Being cutesy has lead to your post being a garbled mess.>>
May 24, 2011
Rank: 5 / 5 (2)
The link you posted supports me completely. Thank you.
You really should read it. Here is the relevant parts. There are two.
I put that one first because that is part that is relevant to evolution.>>
May 24, 2011
Rank: 5 / 5 (2)
Which is what you have been confusing with the mutations that are involved in Natural Selection.>>
May 24, 2011
Rank: 5 / 5 (2)
I am sorry that I didn't understand where you were trying to go. However that was because you don't understand what you were trying to talk about. It doesn't help that you don't want to be honest about your intent either. If you want to have an honest discussion about ID you shouldn't try to hide that you are talking about ID. In case you have not noticed it I don't do sort of hidden agenda post. I think it is duplicitous at best and just plain dishonest in many cases.
Oh and sneering at me when you don't understand what you trying to talk about is silly.
Ethelred
May 24, 2011
Rank: not rated yet